Je Soussigné

Jiaqi Yang

charter on the fight against plagiarism. This work has not been submitted previously either in this country or in another country in the same or in a similar version to any other examination body.

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. In result, it is therefore interesting to alternate cleaning by CB and AB during filtration and it is very important to study the optimum backwash frequency of AB and CB with or without chlorine addition as it has never been done on municipal secondary wastewater effluent. Additionally, the consumption of capital expenditure and operational expenditure provides a direct reference to the industrial scale establishment. Therefore, it is necessary to estimate the economic budget of the project before production and application in industrial scale.

The aim of this thesis is to fully assess the performances of a semi-industrial UF pilot plant as an urban wastewater tertiary treatment for water reuse in terms of: (i) optimization of filtration operating conditions, (ii) permeate water quality, (iii) membrane fouling control and management through a combination of potentially chlorinated CB and/or AB, and (iv) brief calculation of total costs. The drawn conclusions are believed to be applicable for practical operation of semi-industrial UF systems. This subject aims to make comprehensive consideration of the impact conditions on UF system in order to achieve the most economical and efficient filtration and qualified water production. A brief overview of each chapter in the thesis is described below. It is important to note that some parts of this work are synthetized in 3 research articles and one review paper whose references are given in Appendix Ⅱ.

4

, it is necessary to study the microplastics fate in wastewater treatment plant effluent for water reuse.

Chapter 2 introduces the methodology, equipment, and materials used in this thesis together with the detailed information of manufacture, testing institute, and testing process. This chapter summarised the materials, analytical methods, and comparative conditions for the experiments from Chapter 3 to Chapter 5.

Chapter 3 is mainly focused on the optimal operating conditions for sustainable filtration performance. The operating parameters to be optimized include flux, filtration time and backwash sequence which consists of a combination of CB and AB during filtration. The target of this study is to find out the optimized filtration conditions that can be long-term applied on secondary wastewater treatment for water reuse with guarantee of adequate permeate quality, sustainable hydraulic filtration performance, and high net permeate production. 15 different filtration conditions are designed to identify the effects of flux, filtration cycle time, and backwash sequences on hydraulic filtration performance. The filtration performances will be described through the analysis of hydraulic filtration performance, fouling composition and reversibility, water recovery rate, and the impact of AB frequency on irreversible fouling control.

Chapter 4 shows the results of water quality before and after the UF system. The permeate quality, analysed several times and during different seasons, will be compared to the water reuse

Water reuse is an enduring topic that benefits the society and future generations of mankind.

Qualified reuse water not only reduces the occurrence and spread of diseases, but also contributes to the environment protection. In Europe, approximately 2.4% of the total treated wastewater effluents was reused in 2015 [START_REF] Mudgal | European Commission, Directorate-General for the Environment[END_REF], while France only reused around 1% [2]. As the reuse proportion differs a lot among different countries and regions, water reuse market is still young and limited which needs to be highly improved in the future. In this work, water reuse from urban wastewater only, will be considered. Among urban wastewater treatment, primary treatment mostly with physical processes can remove approximately 50-70% of total suspended solids (TSS) and 25-50% of biological oxygen demand after 5 days (BOD5) [3]. The secondary treatment combines biologic and chemical processes to remove the soluble organic matter and the residual TSS [4]. However, the secondary effluent is limited in reuse applications with risks for human health and public environments [5]. To be reused, the secondary effluent needs tertiary and advanced treatments which are considered as the advanced level of treatment and mostly include membrane processes, advanced oxidation processes, disinfection or any combination of them to remove chemical and biologic constituents. Nowadays, more and more advanced treatment technologies for municipal wastewater reuse have emerged, and membrane filtration is one of the main unit technologies. Ultrafiltration (UF) has been accepted as one of the most cost-effective technology to deal with secondary effluent on non-potable reuses, such as agricultural irrigation, landscape irrigation, urban reuse, and process water for industries [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Yang | Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-of-the-Art and Performance Analysis[END_REF][START_REF] Shi | Role of concentration polarization in cross flow micellar enhanced ultrafiltration of cadmium with low surfactant concentration[END_REF][START_REF] Shi | Ultrafiltration of oil-in-water emulsions using ceramic membrane: Roles played by stabilized surfactants[END_REF].

UF enables high removal efficiency on TSS, turbidity, organic matters, and microorganisms, etc [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Qu | Tertiary treatment of secondary effluent using ultrafiltration for wastewater reuse: correlating membrane fouling with rejection of effluent organic matter and hydrophobic pharmaceuticals[END_REF]. Based on scientific consensus and best available evidence, the guidelines from the World Health Organization (WHO) and the French water reuse standards can be both taken into account [START_REF]Guidelines for the safe use of wastewater, excreta and greywater[END_REF][START_REF]relatif à l'utilisation d'eaux issues du traitement d'épuration des eaux résiduaires urbaines pour l'irrigation de cultures ou d'espaces verts -Légifrance[END_REF]. However, regulations are becoming stricter in terms of concentrations of E. coli, BOD5, TSS and turbidity such as in the higher reclaimed water quality class (A) of the recent regulation (EU) 2020/741 of the European Parliament and of the Council of 25 May 2020 on minimum requirements for water reuse [13]. Therefore, there is a need to confirm if UF can meet these new standards and to define for the first time a range of effective operating conditions. Indeed, additionally, membrane fouling limits the economical operation of UF process on wastewater treatment [START_REF] Zheng | Contribution of effluent organic matter (EfOM) to ultrafiltration (UF) membrane fouling: Isolation, characterization, and fouling effect of EfOM fractions[END_REF]. To control fouling, filtration conditions (flux, filtration time, cleaning) need to be optimized because they can directly affect either the formation and nature of the fouling layer, or the removal mechanism of the foulants. Chemical washing is effective guidelines or standards of the World Health Organization (WHO), France, and the recent EU regulation. In addition, the coronavirus Sars-CoV-2 which causes the Covid-19 pandemic and the microplastic particles which become new threats for humans are also tested.

Chapter 5 investigates the influence of chlorine (NaOCl) addition in backwash water on backwash cleaning efficiency and filtration performances to better control the UF membrane fouling. Additionally, this chapter also discusses the influence of chlorinated backwashes on membrane structures, and cleaning mechanisms. The comprehensive analysis of the capital expenditure and operation expenditure of the semi-industrial UF system for water reuse is also discussed in this chapter.

In the final conclusions and perspectives section, all the results obtained in this thesis are summarized, and some further studies about this topic are proposed.

CHAPTER 1. State of the Art

. Interest and definition of water reuse

Water scarcity is growing under the pressures of population growth, climate changes and increased pollution. From the Global Risks report of 2019 provided by the World Economic Forum, more than 650 million people in 500 cities are projected to face declines in freshwater availability of at least 10% in the 2050s, especially in Middle East and North Africa [START_REF] Marsh | The global risks report 2019[END_REF]. Since unsafe wastewater reuse could cause serious catastrophic epidemics of waterborne diseases such as Asiatic cholera and typhoid, the researches on potable water protection and terminal wastewater treatment was then developed, such as the reservoirs or aqueduct systems and filtration [START_REF] Asano | Wastewater reclamation, recycling and reuse: past, present, and future[END_REF]. The US Environmental Protection Agency (EPA) defines wastewater reuse as: using wastewater or reclaimed water from one application for another application [START_REF] Hlavinek | Risk Management of Water Supply and Sanitation Systems[END_REF]. The deliberate use of reclaimed water or wastewater must comply with applicable rules for a beneficial purpose. In fact, qualified reuse water not only reduces the occurrence and spread of diseases, but also contributes to the environment protection. Therefore, recovering water, energy, nutrients and other precious materials embedded in wastewater, is a key opportunity to be seized [START_REF]The international water association[END_REF][START_REF]Wastewater: the untapped resource[END_REF]. Water reuse could also help to regulate climate by increasing natural flows in surface waters (with cascading positive effects on ecosystem health and biodiversity) and may contribute to rising groundwater tables through water reused for crop or landscaping irrigation [START_REF] Lautze | Global experiences in water reuse[END_REF].

As reported by Bixio et al. in 2005 [START_REF] Wintgens | The role of membrane processes in municipal wastewater reclamation and reuse[END_REF], over 3000 water reuse projects distributed in over 60 countries were assessed in an advanced planning phase. Most water recycling schemes are located in Japan (> 1 800) and the US (> 800), then followed by Australia (> 450), Europe (> 200), the Mediterranean and the Middle East area (> 100) and Latin America (> 50). However, the projects number is likely to be higher considering the rapid development of water reuse in China, India and the Middle East [START_REF] Sanz | Water Reuse in Europe -Relevant guidelines, needs for and barriers to innovation[END_REF]. According to J. Yang [START_REF] Yang | Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-of-the-Art and Performance Analysis[END_REF], the reuse proportion varies greatly from country to country, mainly due to geography, technology, and water supply and demand. As reported by Global Water Market in 2017, the total volume of water reuse was approximately 14.2 billion m 3 .y -1 worldwide, less than 4% of domestic wastewater (250 to 350 billion m 3 .y -1 ) [START_REF] Lautze | Global experiences in water reuse[END_REF][START_REF] Tejero | Water Scarcity and Sustainable Agriculture in Semiarid Environment: Tools, Strategies, and Challenges for Woody Crops[END_REF]. Thus, there is a great potential to establish water reuse projects, improve reused water quality and then contribute to reduce water crisis worldwide.

Water reuse applications and guidelines

As the European Parliament estimated in its recent regulation setting minimum requirements for water reuse in agriculture in May 2020, increasing water reuse in agricultural irrigation from 1.7 billion m 3 .y -1 to 6.6 billion m 3 .y -1 by 2025 could reduce water stress by 5% [13]. France, as one of the main member states in the European Union, reused merely 1% of the treated wastewater in 2019 according to the Office International de l'Eau [START_REF]Water Reuse Europe, France wants to triple their water reuse by 2025[END_REF]. To improve water reuse rates, the French government aimed to triple the volumes of reused water by 2025 for nonpotable purposes by introducing regulatory changes [START_REF]Water Reuse Europe, France wants to triple their water reuse by 2025[END_REF]. Generally, non-potable reuse is more likely to build the degree of familiarity and trust required by the public for acceptance, compared to potable reuse [START_REF] Marks | Taking the public seriously: the case of potable and non potable reuse[END_REF]. In the global water reuse market, 97.7% of water production is reused for non-potable purposes, of which 52% is for irrigation and 20% is for industrial process water recirculation. Since the potential for human contact increases with water reuse, advanced treatments beyond secondary urban wastewater treatments are more required, among which membrane filtration is one of the key unit technologies for water reuse as discussed in the next section.

Currently, water reuse has become an attractive option for conserving and extending available water supply, and its applications are shown in Table 1-1 [START_REF] Angelakis | Water scarcity management: part 1: methodological framework[END_REF]. Overall, water reuse plays a significant role in non-potable applications, including non-potable urban reuse, irrigation, recreation impoundment, environmental enhancements, industries and groundwater recharge.

Mainly, the share of reclaimed water is mostly for irrigation, 52% in total, including agricultural irrigation and landscape irrigation [START_REF] Angelakis | Water scarcity management: part 1: methodological framework[END_REF][START_REF] Paul | How scale and technology influence the energy intensity of water recycling systems-An analytical review[END_REF]. Additionally, approximately 20% of reclaimed water is reused for the industrial self-water-circulation systems for resource and money savings.

Municipal or urban wastewater or domestic sewage as the main wastewater sources usually have high levels of organic and inorganic material, pathogenic organisms, nutrients and many toxic elements, including heavy metals [START_REF] Bwapwa | Treatment of Domestic/Municipal and Industrial Wastewater Using Microalgae: Review[END_REF], as stated in Table 1-2.

Table 1-1 Major water reuse applications and constraints worldwide [START_REF] Angelakis | Water scarcity management: part 1: methodological framework[END_REF][START_REF] Paul | How scale and technology influence the energy intensity of water recycling systems-An analytical review[END_REF]. The reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility, for reuse [START_REF] Nolde | Greywater reuse systems for toilet flushing in multi-storey buildingsover ten years experience in Berlin[END_REF]. However, the components and pollutants in wastewater are changeable from source-to-source. Therefore, the treatment processes should vary with the components to be removed. Importantly, different reuse applications require different water quality specifications. Therefore, treatment technologies developed from simple processes into more advanced ones [START_REF] Li | Review of the technological approaches for grey water treatment and reuses[END_REF]. Since not all the wastewater treatment processes could remove contaminants from wastewater completely, the reused water needs to meet the water reuse standards formulated by the government or other qualified authority institutions that work for the applications or emission of effluents. However, there are no uniformly enforceable international water reuse guidelines to control the quality of the reclaimed wastewater. Even for the same water reuse application in the U.S., guidelines vary from state to state. Therefore, countries are looking forward to new regulations referring to international guidelines from the United Nations (UN), the EU Commission or the US EPA to estimate the different criteria needed for better water management [START_REF] Sanz | Water Reuse in Europe -Relevant guidelines, needs for and barriers to innovation[END_REF][START_REF] Racar | Application of UF/NF/RO membranes for treatment and reuse of rendering plant wastewater[END_REF][START_REF] Pidou | Hybrid membrane processes for water reuse[END_REF].

Application

Based on scientific consensus and best available evidence, the World Health Organization (WHO) has set the guidelines for the safe use of wastewater, excreta and greywater, promoting the public health benefits of wastewater, excreta and greywater use in agriculture and aquaculture and is now widely accepted as a benchmark [START_REF]Guidelines for the safe use of wastewater, excreta and greywater[END_REF]. Additionally, the European Parliament published a legislative resolution on May 2020, regulation (EU) 2020/741 of the European Parliament and of the Council on minimum requirements for water reuse (15301/2/2019-C9-0107/2020-2018/0169(COD)) [13]. This official regulation project defines the water quality limits and obligations of wastewater treatment plant (WWTP) operators, for water reuse in the field of agricultural irrigation only. The above-mentioned reuse guidelines, as the representatives concerning the parameters of water quality, are presented in Table 1-3. To be noted, some parameters mentioned in the EU regulation are not included in Table 1-3. These parameters and associated limits are the Legionella spp. should <1 000 CFU•L -l where there is risk of aerosolisation in greenhouses,and the Intestinal nematodes (Helminth eggs) should ≤1 egg•L -l for irrigation of pastures or forage.

In fact, most countries supplement and develop their own guidelines, based on WHO guidelines-and considering their potential specifications. Overall, the following parameters: pH, total suspended solids (TSS), biological oxygen demand after 5 days (BOD5), turbidity, total coliform and fecal coliforms are important parameters to evaluate the water quality all over the world, and they will be considered to evaluate the ability of some water reuse technologies in the following parts of this study. The choices of wastewater treatment technologies may be affected by the following factors [START_REF] Needs | Water Reuse: Potential for Expanding the Nation's Water Supply Through Reuse of Municipal Wastewater[END_REF]: reclaimed water objectives for application, wastewater characteristics, compatibility with existing conditions, process flexibility, operating and maintenance requirements, energy and chemical requirements, economical requirements, residual disposal options and environmental constraints. In general, in a WWTP, if the wastewater, after primary and/or secondary treatment, cannot be reused for target purposes, it should be treated to tertiary level or with more advanced processes to achieve reuse standards. Meet requirements for safe drinking water; specific guidelines do not exist.

ND, not detected; NTU, nephelometric turbidity units; ABCD represents the different water quality levels, A being the best, D being the worst.

Focus on the pollution by microplastic particles

Even if microplastic particles (MPs) are not mentioned yet in the water reuse standards or guidelines as they are not even mentioned in drinking water standards because standards for detection and quantification are just being elaborated, it is a pollutant of main interest. Indeed, currently, more and more researches, especially on microplastic sources, pollutions, transport, harmfulness, retention, recovery methods, and analytical methods, have been developed [START_REF] Can-Güven | Microplastics as emerging atmospheric pollutants: a review and bibliometric analysis[END_REF].

Defined by [START_REF] Frias | Microplastics: Finding a consensus on the definition[END_REF], MPs are either synthetic solid particles or polymeric matrix, with size ranging from 1 μm to 5 mm, from primary or secondary manufacturing origin, and are insoluble in water. MPs can be easily swallowed by organisms and accumulated due to their physical properties such as small particle sizes and widespread distribution [START_REF] Rillig | Microplastic in Terrestrial Ecosystems and the Soil?[END_REF].

Normally, plastics have stable chemical properties that can stay for hundreds to thousands of years in nature. MPs do not cause fatal effects on living organisms, but they would cause chronic toxicity, which is considered as a key issue for long-term exposure. There are several mechanisms for microplastics to cause toxic effects. First, some polymer materials can directly release toxicity, such as polyvinyl chlorides (PVC), Polyurethanes (PUR), polyacrylonitriles (PAN), and Polystyrene (PS) etc. PVC can release dioxins, phthalates, vinyl chloride, ethylene dichloride, and other toxic chemicals. PS is found to be translocated in blood circulation and cause reproductive disruption for marine filter feeders [START_REF] Sussarellu | Oyster reproduction is affected by exposure to polystyrene microplastics[END_REF][START_REF] Chen | Quantification of extrapulmonary translocation of intratracheal-instilled particles in vivo in rats: Effect of lipopolysaccharide[END_REF]. All of them can leech harmful chemicals into the water or food and get into human bodies through food chains. Second, microplastics can carry toxic and harmful substances. MPs are prone to be gathered with other particles or suspended solids in waters as plastics tend to be more hydrophobic [START_REF] Nguyen | Separation and Analysis of Microplastics and Nanoplastics in Complex Environmental Samples[END_REF]. Highly toxic substances such as Dichloro-diphenyl-trichloroethane (DDT), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), nonylphenols and other nonpolar substances can adsorb on microplastic surfaces that can be transported and bioaccumulated through food chain [START_REF] Fisner | Concentration and composition of polycyclic aromatic hydrocarbons (PAHs) in plastic pellets: Implications for small-scale diagnostic and environmental monitoring[END_REF][START_REF] Nobre | Assessment of microplastic toxicity to embryonic development of the sea urchin Lytechinus variegatus (Echinodermata: Echinoidea)[END_REF]. Besides, some additives added by manufacturers such as plasticizers, stabilizers and pigments to plastics, mostly are hazardous substances. Third, MPs can be further degraded to the smaller pieces, for example, nanoplastics (< 1μm), and may become more dangerous for human health [START_REF] Jambeck | Plastic waste inputs from land into the ocean[END_REF]. Ragusa et al. [START_REF] Ragusa | Plasticenta: First evidence of microplastics in human placenta[END_REF] have already discovered the presence of MPs (5-10μm) in human placenta, reflecting that the MPs can be absorbed into human bloodstream and be transferred among organs which will potentially reduce the bodies defense mechanisms against pathogens.

Nowadays, the demand of plastics in our daily life is largely increased, global plastics production has reached up to 368 million tons in 2019 (PlasticsEurope 2020), thus lots of plastic waste eventually flows into the oceans and wastewater system [START_REF] Thompson | Lost at Sea: Where Is All the Plastic?[END_REF][START_REF] Zhang | A Review of Microplastics in Table Salt, Drinking Water, and Air: Direct Human Exposure[END_REF][START_REF] Zhang | Atmospheric microplastics: A review on current status and perspectives[END_REF]. Liu et al. [START_REF] Liu | A review of the removal of microplastics in global wastewater treatment plants: Characteristics and mechanisms[END_REF] investigated 38

WWTPs in 11 countries and found that the abundance of MPs in influent ranged from 0.28 MP•L -1 to 3.14 × 10 4 MP•L -1 , while that in the effluent ranged from 0.01 MP•L -1 to 2.97 × 10 2 MP•L -1 . For example, in raw wastewater, 130 MP•L -1 was detected by Ben-David et al. [START_REF] Ben-David | Microplastic distributions in a domestic wastewater treatment plant: Removal efficiency, seasonal variation and influence of sampling technique[END_REF] and 58 MP•L -1 was detected by Lares et al. [START_REF] Lares | Occurrence, identification and removal of microplastic particles and fibers in conventional activated sludge process and advanced MBR technology[END_REF]. In this case, wastewater treatment plants (WWTPs)

serve as an important route for MPs to the environment. Many researchers reported that WWTPs with tertiary treatment process or membrane bioreactor treatment could achieve higher removal of MPs from raw wastewater. For example, Ben-David et al. [START_REF] Ben-David | Microplastic distributions in a domestic wastewater treatment plant: Removal efficiency, seasonal variation and influence of sampling technique[END_REF], Lares et al. [START_REF] Lares | Occurrence, identification and removal of microplastic particles and fibers in conventional activated sludge process and advanced MBR technology[END_REF], and Simon et al. [START_REF] Simon | Quantification of microplastic mass and removal rates at wastewater treatment plants applying Focal Plane Array (FPA)-based Fourier Transform Infrared (FT-IR) imaging[END_REF] all confirmed that the WWTPs can remove more than 97% of 10-500 μm sized MPs.

In fact, the presence of smaller MPs increases the difficulty of detection and tracking, the difficulty of removal, and also increases the potential threat for natural environment and organisms. Therefore, it is necessary to find more accurate analysis method and the effective treatment process to reduce the MPs exposure to human and organisms.

Membrane-based technology for water reuse

In the context of municipal (urban) wastewater treatment, primary treatment can be considered as physical processes such as sedimentation and flotation [START_REF] Smith | Can China reduce energy for water? A review of energy for urban water supply and wastewater treatment and suggestions for change[END_REF]. The process can remove approximately 50-70% of total suspended solids (TSS) and 25-50% of BOD5 [3]. The secondary treatment combines biologic and chemical processes to remove the soluble organic matter and the residual TSS after the primary process, such as activated sludge, oxidation ponds and rotating biologic contactor [4]. However, the secondary effluent is limited in reuse applications with risks for human health and public environments [5]. A tertiary treatment could then be applied to remove associated hazards and health risks [5]. Tertiary and advanced treatments are considered as the advanced level of treatment and mostly include membrane processes, advanced oxidation processes, disinfection or any combination of them to remove chemical and biologic constituents. In order to make reuse cost-effective, the level of treatment must be "fit for purpose". Treatment technologies are employed either alone or in combination to achieve wastewater reuse levels. However, as the potential for human contact increases, advanced treatment beyond secondary treatment becomes more accepted, and membrane filtration is one of the key unit technologies for water reuse. Although several review articles have given overview summaries of the previously reported techniques for municipal wastewater reuse [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Wu | Membrane-based technology in greywater reclamation: A review[END_REF][START_REF] Cherchi | Municipal reclaimed water for multi-purpose applications in the power sector: A review[END_REF][START_REF] Song | Resource recovery from wastewater by anaerobic membrane bioreactors: Opportunities and challenges[END_REF][START_REF] Diaz-Elsayed | Wastewater-based resource recovery technologies across scale: A review[END_REF], they either mainly focused on greywater reuse or on only one reuse level or on only one type of technology. Therefore, membrane-based municipal wastewater treatment techniques for reuse have not been extensively reviewed.

This section aims to provide a comprehensive view on membrane-based processes used in municipal wastewater treatment for water reuse. Particularly, this review is expected to provide an overall summary of reported research cases of feasible membrane-based technologies on urban wastewater treatment for reuse, mainly focusing on membrane hydraulic performance, contaminants removal ability, reuse purposes and energy consumption. Key benefits and challenges of current implementations will be also described after the summary.

Performances of Membrane-Based Treatment Processes for Municipal Water Reuse

Membrane-based technologies are advanced treatment process for municipal wastewater treatment [START_REF] Gupta | Application of low-cost adsorbents for dye removal -A review[END_REF]. Pressure-driven membrane processes are presented in Table 1-4 and can be classified into four main categories based on the different selective pore size: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO), [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Lee | A review of reverse osmosis membrane materials for desalination-Development to date and future potential[END_REF][START_REF] Shon | Nanofiltration for water and wastewater treatment -A mini review[END_REF][START_REF] Padaki | Membrane technology enhancement in oil-water separation. A review[END_REF][START_REF] Van Der Bruggen | Drawbacks of applying nanofiltration and how to avoid them: A review[END_REF]. The selection of material is affected by pore size distribution, wetting susceptibility, porosity, mechanical strength, cost, polymer flexibility, fouling resistance, stability, durability and chemical resistance [START_REF] Bruggen | A review of pressure-driven membrane processes in wastewater treatment and drinking water production[END_REF]. As the pores get smaller, the membrane needs more driving force to be operated [START_REF] Bruggen | A review of pressure-driven membrane processes in wastewater treatment and drinking water production[END_REF][START_REF] Tchobanoglous | Wastewater Engineering Treatment and Resource Recovery[END_REF]. Membrane fouling always occurs during the filtration process, followed with an increase in transmembrane pressure (TMP) to maintain a constant flux or followed with a decrease in flux for a constant TMP. According to Guo et al. [START_REF] Guo | A mini-review on membrane fouling[END_REF], membrane fouling is often defined based on the type of pollutants present in the feed stream and can be classified into four categories, including: (1) particulate/colloidal fouling, when suspended solids and/or colloids clog the pores of a membrane or adhere to its surface; (2) organic fouling, when reactive dissolved organic components or colloids attach to the membrane by adsorption; (3) inorganic fouling, also known as scaling or precipitation fouling, caused by the presence of crystallized salts, oxides or hydroxides in the feed solution that are prone to precipitate onto membrane surface due to pH change or oxidation; and (4) biofouling, caused when microorganisms, plants, algae or other biologic contaminants grow on or in the membrane surface and pores. Each type of fouling can be either reversible or irreversible by membrane cleaning step and permanently compromise its performance. All the fouling types can take place simultaneously, and the interaction between them usually increases filtration resistance [START_REF] Lin | A review on anaerobic membrane bioreactors: Applications, membrane fouling and future perspectives[END_REF]. Therefore, in each membrane process, fouling issues need to be considered and optimized to obtain sustainable conditions and excellent filtration performance. Additionally, an important notion to take into account is the threshold flux, the flux at or below which a low and near constant fouling rate occurs, but above which the fouling rate increases markedly [START_REF] Field | Critical, sustainable and threshold fluxes for membrane filtration with water industry applications[END_REF][START_REF] Eric | Evaluation of Membrane Processes for Reducing Total Dissolved Solids Discharged to the Truckee River[END_REF]. The number of studies on critical, sustainable and threshold flux of different kinds of wastewater filtrated by certain membranes are expanding recently because these concepts of flux are highly related to control low fouling rates on membranes [START_REF] Field | Critical, sustainable and threshold fluxes for membrane filtration with water industry applications[END_REF][START_REF] Nguyen | Critical flux-based membrane fouling control of forward osmosis: Behavior, sustainability, and reversibility[END_REF][START_REF] Bacchin | Critical and sustainable fluxes: Theory, experiments and applications[END_REF]. Especially for commercial and industrial production, the operation at sustainable flux could definitely control fouling and at the same time, give an optimal balance between moderate operating costs and moderate capital costs [START_REF] Field | Critical, sustainable and threshold fluxes for membrane filtration with water industry applications[END_REF]. The definition of the sustainable conditions appears as a challenge for each new membranebased treatment processes for municipal water reuse.

MF/UF-based Treatment Processes After Secondary Treatment of WWTP

MF and UF can remove particles larger than their pore size mainly through sieving mechanism [START_REF] Bruggen | A review of pressure-driven membrane processes in wastewater treatment and drinking water production[END_REF][START_REF] Gallego-Molina | Reducing pollution from the deliming-bating operation in a tannery. Wastewater reuse by microfiltration membranes[END_REF]. In general, the MF process alone can effectively remove high molecular weight organic matters, suspended solids, colloids, bacteria and thus reduce turbidity. Compared to MF, UF membrane has wider separation ranges with smaller pore size and enhanced removal ability for particles, colloids, and more importantly, bacteria with high removal rate and viruses. In order to clearly understand the difference between MF and UF, Tchobanoglous et al. [START_REF] Tchobanoglous | Wastewater Engineering Treatment and Resource Recovery[END_REF] quoted by the review of Warsinger et al. [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF], summarized the rejection characteristics when filtrating the same secondary effluent by MF and UF, on bacteria, viruses and other essential water quality parameters such as TSS, chemical oxygen demand (COD) and TDS. It should be noted at first that the data gave general information with certain limitations: the actual performance may vary related to different conditions, such as temperature, flow rate and transmembrane pressure (TMP). From the review [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF], MF is almost as efficient as UF in removing TSS and BOD5, of which the removal rates range from 95% to 99.9% and from 75% to 90%, respectively. Furthermore, the efficiencies of UF on COD and total organic carbon (TOC) concentrations removal are about 5% to 20% higher than MF. More importantly, UF provides almost complete removal of bacteria, protozoa and viruses, which is one of the main advantages compared to MF. MF can partially remove viruses and protozoa through adhering to impurities in wastewater like protein, colloids or coliforms, but microorganisms can still pass through MF membranes since the pore size is larger than the virus size [START_REF] Wintgens | The role of membrane processes in municipal wastewater reclamation and reuse[END_REF]. In 1995, Madaeni et al. [START_REF] Madaeni | Virus removal from water and wastewater using membranes[END_REF] have verified that the presence of bacteria (E. coli) and turbidity highly contributed to the poliovirus rejection through 0.22 μm MF under TMP between 0.5 and 1 bar. Huang et al. [START_REF] Huang | Mechanisms of virus removal from secondary wastewater effluent by low pressure membrane filtration[END_REF] demonstrated that virus (MS2 bacteriophage as an indicator) is more likely to be removed through 0.1 μm-MF in waters with more organic matters or higher concentration of large molecular weight organic foulants. Herath et al. [START_REF] Herath | Removal of viruses by microfiltration membranes at different solution environments[END_REF] successfully observed a considerably high virus rejection rate at their isoelectric point when using a 0.2 μm MF membrane to filtrate the specific virus (19 to 80 nm) solutions due to the virus-virus coagulation and virus-protein coagulation. In addition, the physicochemical properties of the virus, the membrane material, the feed, as well as the hydraulics of the filtration process could affect virus removal by MF [START_REF] Huang | Mechanisms of virus removal from secondary wastewater effluent by low pressure membrane filtration[END_REF][START_REF] Langlet | Efficiency of MS2 phage and Qβ phage removal by membrane filtration in water treatment: Applicability of real-time RT-PCR method[END_REF][START_REF] Herath | The effect of suction velocity on concentration polarization in microfiltration membranes under turbulent flow conditions[END_REF]. For example, Huang et al. [START_REF] Huang | Mechanisms of virus removal from secondary wastewater effluent by low pressure membrane filtration[END_REF] recorded that when adding sodium or calcium to feed water, the virus removal capacity decreased immediately. Besides, low pH value increases virus removal while higher pH value makes removal rate decrease [START_REF] Herath | Removal of viruses by microfiltration membranes at different solution environments[END_REF]. Anyway, the removal of viruses through MF is significant but not complete because the virus are still able to pass through membrane pores [START_REF] Xiang | Evaluation of virus removal in MBR using coliphages T4[END_REF]. It is reported by Warsinger et al. [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF] that the log removal value of MF processes on viruses ranges from 0 to 2 (equals to 0% to 99%). Furthermore, according to Warsinger et al. [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF], UF can support up to 6 log removal of bacteria and up to 7 log removal of viruses, and if there are protozoa, UF can remove protozoan cysts and oocysts to more than 6 log reduction. Therefore, UF process provides more safer and more reliable water product than MF process. At present, ultrafiltration (UF) has been widely accepted as one of the most costeffective technology to deal with secondary effluent on non-potable reuses, such as agricultural irrigation, landscape irrigation, urban reuse, car washing, and sometimes as process water for industries [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF]. Table 1-5 summarizes the real cases of MF/UF-based processes applied after secondary treatment for water reuse. In results, among the literature about the MF/UF-based process applied on water reuse (Table 1-5), 60% of the lists are UF-based treatment processes that achieved water reuse and met standards. UF enables high removal efficiency on total suspended solids (TSS), turbidity, and partial removal efficiency on organic matters [START_REF] Qu | Tertiary treatment of secondary effluent using ultrafiltration for wastewater reuse: correlating membrane fouling with rejection of effluent organic matter and hydrophobic pharmaceuticals[END_REF]. More importantly, UF can retain microorganisms significantly, including bacteria, protozoa, and viruses [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Gómez | A comparative study of tertiary wastewater treatment by physico-chemical-UV process and macrofiltration-ultrafiltration technologies[END_REF]. In early 1998, G. Tchobanoglous et al. [START_REF] Tchobanoglous | Ultrafiltration as an advanced tertiary treatment process for municipal wastewater[END_REF] had already applied the UF membrane (hollow fiber, polysulfone) on treatment of secondary and tertiary municipal wastewater with good results. J. Arévalo et al. [START_REF] Arévalo | Wastewater reuse after treatment by tertiary ultrafiltration and a membrane bioreactor (MBR): a comparative study[END_REF] confirmed the effectiveness of both hollow fiber and flat-sheet UF membranes on removal of particles, organics, and microorganisms from wastewater. On reuse purpose, the investigation of [START_REF] Muthukumaran | Performance evaluation of different ultrafiltration membranes for the reclamation and reuse of secondary effluent[END_REF] [START_REF] Muthukumaran | Performance evaluation of different ultrafiltration membranes for the reclamation and reuse of secondary effluent[END_REF], and [START_REF] Pollice | Tertiary filtered municipal wastewater as alternative water source in agriculture: a field investigation in Southern Italy[END_REF] [START_REF] Pollice | Tertiary filtered municipal wastewater as alternative water source in agriculture: a field investigation in Southern Italy[END_REF] or [START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF] [START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF] all confirmed that UF (with prefilter) can be successfully applied on secondary effluent treatment for reuse in agriculture with respect to WHO guidelines in terms of permeate quality respectively with synthetic and real secondary effluent as feed. These three studies were all conducted in pilot-scale operation ranging from 2 months to 2 years and with pore sizes ranging from 0.002μm (1kD) to 0.03μm. In Table 1-5, only one reference demonstrates MF process alone on achieving water reuse. Ahn et al. [START_REF] Ahn | Treatment of domestic wastewater using microfiltration for reuse of wastewater[END_REF] showed that MF permeate can be used to clean building floors or flush toilets, but they did not state the water reuse standard that they referred to. When comparing their permeate quality with WHO guidelines, the detected parameters are incomplete and substandard, e.g., the turbidity in both cases exceeds the limit of WHO guidelines (turbidity ≤ 2 NTU). The other listed MF processes were all combined with chemical and physical processes, or UF process to finally achieve water reuse purposes.

Moreover, chemical and/or physical processes such as sedimentation, adsorption, flocculation and coagulation [START_REF] Matilainen | Natural organic matter removal by coagulation during drinking water treatment: A review[END_REF][START_REF] Guo | Experimental investigation of adsorption-flocculation-microfiltration hybrid system in wastewater reuse[END_REF][START_REF] Karakashev | Innovative process scheme for removal of organic matter, phosphorus and nitrogen from pig manure[END_REF] can be used as pretreatment of membrane processes to decrease membrane fouling potential and improve filtration performance [START_REF] Guo | Experimental investigation of adsorption-flocculation-microfiltration hybrid system in wastewater reuse[END_REF][START_REF] Hatt | Precoagulation-microfiltration for wastewater reuse[END_REF][START_REF] Konieczny | A coagulation-MF system for water treatment using ceramic membranes[END_REF]. For example, Al2(SO4)3, Fe2(SO4)3, FeCl3 and polyaluminum chloride can be used as remarkable coagulants [START_REF] Hatt | Precoagulation-microfiltration for wastewater reuse[END_REF]. Activated carbon (AC) is a widely accepted adsorbent for adsorption [START_REF] Seo | Biological powdered activated carbon (BPAC) microfiltration for wastewater reclamation and reuse[END_REF]. It can be used as a powder (PAC) in dispersion or as granules (GAC) in fixed bed. Pretreatment process helps to clean the feed water for MF/UF and contributes to remove the fouling potentials before MF/UF membranes, thus contributing to prolong the whole system operational time, improving permeability recovery, and decreasing membrane cleaning chemicals consumption.

As stated by Zheng et al. [START_REF] Zheng | Effect of slow sand filtration of treated wastewater as pre-treatment to UF[END_REF], when studying the time required to increase TMP from 0.22 bar to 0.7 bar on secondary effluent treatment (constant flux of 50 L•m -2 •h -1 ), direct UF process took only 12 h while the sand-UF system could extend to 30 days. In addition, Fan et al. [START_REF] Fan | Low-pressure membrane filtration of secondary effluent in water reuse: Pre-treatment for fouling reduction[END_REF] designed parallel tests of MF with/without pretreatment to treat secondary effluent under constant TMP (0.70 bar), the results confirmed that the coagulation-prefiltration (1.5 μm)-MF systems could improve flux recovery (J/J0) between 20% and 30% higher than MF alone due to the hydraulically irreversible fouling (internal adsorptive fouling) reduction by coagulation.

First, it should be noted that in some pretreated processes, for example coagulation with settling, the re-growth of flocs could conversely cause severe cake fouling on membranes [START_REF] Barbot | Coagulation of bentonite suspension by polyelectrolytes or ferric chloride: Floc breakage and reformation[END_REF]. It is necessary to add another prefilter after coagulation, flocculation and settling to remove the flocs, colloids and other particles before the membranes. Second, it has been proven that pretreatment processes could effectively remove natural organic matter (NOM) and colloids [START_REF] Prihasto | Pre-treatment strategies for seawater desalination by reverse osmosis system[END_REF][START_REF] Shon | Fouling of ultrafiltration membrane by effluent organic matter: A detailed characterization using different organic fractions in wastewater[END_REF]. As described previously, dissolved organic carbon (DOC) cannot be effectively retained by MF or UF due to membrane pore sizes being much larger than the related organic molecules [START_REF] Fabris | Pre-treatments to reduce fouling of low pressure micro-filtration (MF) membranes[END_REF]. Fan et al. [START_REF] Fan | Low-pressure membrane filtration of secondary effluent in water reuse: Pre-treatment for fouling reduction[END_REF] reported that MF could only remove 3.9% of DOC, while UF could remove 24.7%. Therefore, when pre-coagulated with 5 mg•L -1 of Al 3+ , the MF system could increase 10% to 15% DOC removal; and when pretreated with 10 mg•L -1 anion exchange resin in wastewater which removes primarily lower molecular weight cut-off (MWCO) and negatively charged organic fractions, the MF and UF systems could improve DOC removal to 58.8% and 68.3%, respectively [START_REF] Fan | Low-pressure membrane filtration of secondary effluent in water reuse: Pre-treatment for fouling reduction[END_REF]. Third, pretreatment processes contribute to the removal of dissolved nutrients, mainly nitrogen and phosphorus. Hybrid precipitation-MF system by Lu et al. [START_REF] Lu | Removal of phosphate and fluoride from wastewater by a hybrid precipitation-microfiltration process[END_REF] made use of calcium salt to increase precipitates involved with phosphorus and fluorine and then separated solid-liquid phases by a following crossflow MF for separation. Guo et al. [START_REF] Guo | Experimental investigation of adsorption-flocculation-microfiltration hybrid system in wastewater reuse[END_REF] compared the performance of MF with and without pretreatment for wastewater reuse, the results showed that MF alone only removed 20% of TOC and 5% of PO4 3-, while pretreated with flocculation and adsorption, the removal efficiency of TOC reached 99.7% and more than 97% of PO4 3-. In addition, the UF system coupled with PAC can be used to eliminate both DOC and micropollutants. Though MF/UF alone is inadequate for micropollutant removal, in PACmembrane processes, contaminants (including natural disinfection byproduct precursors) can be reduced through adsorption onto the activated carbon particles, which are then separated from water by either UF or MF [START_REF] Wintgens | The role of membrane processes in municipal wastewater reclamation and reuse[END_REF]. Among MF-based treatments in Table 1-5, the hybrid physical/chemical process with MF can improve the water quality to meet with reuse standards. However, based on the WHO water reuse guidelines, MF permeate is mostly applied in low levels of non-potable reuse, such as toilet flushing, machine cleaning, irrigation for non-food crops or more likely reused as process water for industries, such as washing, cooling and circulating. Among UF-based treatments in Table 1-5, the hybrid flocculation, coagulation or adsorption process with UF processes, could almost completely remove turbidity, TSS, color from secondary treated municipal WWTP, and the removal of COD, DOC, metal and salt ions was also improved and higher than MF. In addition, pretreatment is mostly used to decrease fouling potential for UF especially when the feed water quality is not very good, in order to provide sustainable filtration performance and reduce operating cost of the whole system.

Additionally, pretreatment can also bring troubles. When pretreated with adsorption, the disadvantages include the expensive regeneration of the adsorbents (such as PACs) and loss of adsorbents [START_REF] Crini | Advantages and disadvantages of techniques used for wastewater treatment[END_REF]. Moreover, pretreatment with coagulation, flocculation and adsorption need higher energy cost with increased sludge volume production during treatment [START_REF] Crini | Adsorption-Oriented Processes Using Conventional and Non-conventional Adsorbents for Wastewater Treatment[END_REF].

Generally, effluents from WWTPs still carry high TSS and NOMs which are prone to cause the formation of fouling on the MF/UF membrane easier. In fact, dissolved organic matters cannot be removed effectively by MF or UF systems, but conversely it can be the main cause of fouling formation on the membrane, finally resulting in shortening membrane lifespan, reducing flow rate, increasing TMP and energy consumption [START_REF] Ang | A review on the applicability of integrated/hybrid membrane processes in water treatment and desalination plants[END_REF][START_REF] Yue | Effects of dissolved organic matters (DOMs) on membrane fouling in anaerobic ceramic membrane bioreactors (AnCMBRs) treating domestic wastewater[END_REF]. Considering the hydraulic filtration performances (Table 12345), almost all researchers were interested in fouling control.

Under constant permeate flux of 20 L•m -2 •h -1 , reported by Falsanisi et al. [START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF], the TMP on UF would increase fast from 0.3 bar to almost 1.2 bar in only 20 min filtration, and permeability decreased from 150 to about 10 L•m -2 •h -1 •bar -1 . While, according to Pollice et al. [START_REF] Pollice | Tertiary filtered municipal wastewater as alternative water source in agriculture: a field investigation in Southern Italy[END_REF], with a periodic filtration cycle of the permeate (90-360 s) and a backwash of (30-40 s) in continuous operational process on secondary effluent treatment in autumn, the system could slow down the increase of TMP on UF which increased from less than 0.1 bar to about 0.7 bar in more than 30 days under almost stable flux at 20 L•m -2 •h -1 . Therefore, periodic backwashes could prolong the UF operation time, reduce the frequency of chemical cleaning uses and save energy during long term operation. Therefore, to support sustainably high performance of MF/UF on wastewater treatment in long term operations, it is necessary to conduct suitable physical and chemical cleaning on membranes.

In summary, direct MF is less used for water reuse treatment due to lower removal efficiency on microorganism and organic matters. The hybrid MF with physical/chemical processes sometimes can improve the water product quality to reuse levels but are low levels due to more healthy concerns. In comparison, UF is more recommended for water reuse treatment than MF. UF has higher removal capacity than MF on various water parameters, such as TOC, COD, turbidity, etc. Moreover, UF can theoretically completely remove microorganisms while MF cannot. Additionally, either UF process alone or hybrid with physical/chemical process can produce qualified water for reuse purpose. The pretreatment before UF is mainly to decrease fouling potential especially when the feed water contains more TSS, organic matters, or particles but the pretreatments need higher costs. This is why hybrid MF or UF was not selected in this work. The limitation of UF-based treatment on potable reuse may be the residual dissolved organic matters, micropollutants, residual nutrients such as phosphorus, nitrates and ammonium, and specific toxic ions produced from coagulants or flocculants (such as chloride ions). In this case, the permeate of UF as the main technology for reclamation is commonly reused on non-potable applications. UF-based processes are more acceptable with respect to water reuse guidelines compared to potable reuse. Coliphages: 10 3 -10 4 PFU•100 mL -1 Turbidity: 0-0.9 NTU TSS: 1-7 mg•L -1 T-UV253.7(%): 0 Nematode eggs: 0 E. coli: 0 CFU•100 mL -1 Fecal coliforms: 0-9 CFU•100 mL -1 Coliphages: 0-1 PFU•100 mL -1 Not mentioned Water reuse guidelines of US EPA [START_REF] Gómez | A comparative study of tertiary wastewater treatment by physico-chemical-UV process and macrofiltration-ultrafiltration technologies[END_REF][START_REF] Gómez | Urban wastewater disinfection by filtration technologies[END_REF] A: absorbance; CFU: colony forming unit; EC: electrical conductivity; LRV: log10 removal value; SAC: spectral absorption coefficient; PPCPs: pharmaceuticals and personal care products

MBR-Based Treatment for Water Reuse

Besides of chemical and physical processes, biologic processes could also be combined with a membrane system based on its advantage in the degradation of microorganisms [START_REF] Leal | Bioflocculation of grey water for improved energy recovery within decentralized sanitation concepts, Bioflocculation Grey Water Improv[END_REF]. The activated sludge process (CAS) is a biologic process that is mainly used for reduction of organic matters in the wastewater, and usually includes an aeration tank used for biologic degradation and a secondary clarifier (sedimentation tank), where the sludge is separated from the treated effluent [START_REF] Wang | Distribution and transformation of molecular weight of organic matters in membrane bioreactor and conventional activated sludge process[END_REF]. The effect of the membrane is to increase the concentration in the biologic reactor, to retain the particulate phase within the bioreactor and allow permeate to the next process or to be discharged/reused [START_REF] Ottoson | Removal of viruses, parasitic protozoa and microbial indicators in conventional and membrane processes in a wastewater pilot plant[END_REF]. In MBRs, biodegradation and membrane separation are performed simultaneously, thus maximizing wastewater treatment efficiency [START_REF] Judd | The MBR Book: Principles and Applications of Membrane Bioreactors for Water and Wastewater Treatment[END_REF]. A review by Wu et al. [START_REF] Wu | Membrane-based technology in greywater reclamation: A review[END_REF] detailed the non-potable and potable application of various MBR systems for greywater reclamation with numerous MBRs case analysis. The reclaimed water is proved to satisfy the guidelines of US EPA and WHO reuse applications. It is reported that the MBRs performed better in the removal of organic matters, resulting in relatively less energy and economy consumption compared with conventional CAS processes. In addition, Wu et al. [START_REF] Wu | Membrane-based technology in greywater reclamation: A review[END_REF] and Atasoy et al. [START_REF] Atasoy | Membrane Bioreactor (MBR) Treatment of Segregated Household Wastewater for Reuse[END_REF] both stated that greywater produced less organic foulant for MBRs together with the lower driving force and lower membrane fouling. Studies summarized in Table 1-6 are focused on MBRs for municipal wastewater treatment and reuse applications. MBRs have been reported to consistently achieve removal rates of 90-95% for COD, 80-99% for NH4-N and 70-99% for total phosphorus (TP), respectively [START_REF] Hai | Membrane Biological Reactors: Theory, Modeling, Design, Management and Applications to Wastewater Reuse -Second Edition[END_REF]. Although feed characteristics among various municipal WWTPs showed large differences, the results of organic removal ratios in the MBRs presented only slight dissimilarities. The application of reclaimed municipal water can be in nonpotable uses with MBRs or additional processes. In addition, MBRs can be operated at wider organic loading rates, higher concentration of mixed liquor suspended solids (MLSS) and larger amount of feed flows. This view can be supported by Tam et al. [START_REF] Tam | A pilot study for wastewater reclamation and reuse with MBR/RO and MF/RO systems[END_REF] who described the separately MBR and MF processes on the same sewage treatment, when the water production both achieved the reuse level for toilet flushing, the MF feed was secondary treated effluent whereas the MBR feed was just degritted sewage. Nevertheless, MBRs are confirmed to produce high qualified water production even under higher concentration of COD, BOD5, TSS, TN, TP and turbidity in the feed. Studies have demonstrated that MBR treatment removed different types of microorganisms, including enteric viruses in some studies, more effectively than in conventional secondary treatment, on both pilot-scale and within full-scale municipal WWTPs [START_REF] Ottoson | Removal of viruses, parasitic protozoa and microbial indicators in conventional and membrane processes in a wastewater pilot plant[END_REF][START_REF] Francy | Comparative effectiveness of membrane bioreactors, conventional secondary treatment, and chlorine and UV disinfection to remove microorganisms from municipal wastewaters[END_REF][START_REF] Farahbakhsh | Removal of coliphages in secondary effluent by microfiltration-mechanisms of removal and impact of operating parameters[END_REF]. Chaudhry et al. [START_REF] Chaudhry | Mechanisms of Pathogenic Virus Removal in a Full-Scale Membrane Bioreactor[END_REF] demonstrated the MBR process could provide more than 4-log reduction of adenovirus and norovirus GII and over 5-log reduction of F + coliphage, and provided evidence for assigning virus disinfection credit to similar MBRs for reclaim wastewater [START_REF] Chaudhry | Mechanisms of Pathogenic Virus Removal in a Full-Scale Membrane Bioreactor[END_REF]. It is important to note that the removal value is a function of the inlet concentration and outlet after MBR and the inlet concentration is at least two times higher in MBR treatment than in CAS treatment. Nevertheless, the above cases confirmed the stable effectiveness of MBRs on certain bacteria removal whatever the pore sizes, but it is not for all microorganisms. Other studies draw a similar conclusion on the removal of seeded viruses in MBRs with LRVs ranging greatly from 0.4 to 5.8 with membrane pore sizes ranging from 0.1 to 0.4 μm [START_REF] Lv | Virus removal performance and mechanism of a submerged membrane bioreactor[END_REF][START_REF] Shang | Bacteriophage MS-2 removal by submerged membrane bioreactor[END_REF].

However, size exclusion by the membrane is probably the dominant removal mechanism for bacteria and viruses in MBRs with intact membranes, but not exclusively. Other removal mechanisms, such as adsorption to the biomass, pore blocking and pore constriction may also play an important role [START_REF] Hirani | Peak flux performance and microbial removal by selected membrane bioreactor systems[END_REF].

Furthermore, the effective biodegradation integrated with membrane performance leads to more advantages than separated processes, i.e., less organic foulants on the membrane, smaller footprint, faster plant activation, no biologic sedimentation units and less sludge production [START_REF] Zanetti | Performance of a full-scale membrane bioreactor system in treating municipal wastewater for reuse purposes[END_REF][START_REF] Quist-Jensen | Membrane technology for water production in agriculture: Desalination and wastewater reuse[END_REF]. As a result, (1) particle separation can be achieved without sedimentation before MBR systems, but with membrane filtration [START_REF] De Luca | Removal of indicator bacteriophages from municipal wastewater by a full-scale membrane bioreactor and a conventional activated sludge process: Implications to water reuse[END_REF]; (2) sludge production from MBRs is lower than CAS [START_REF] Lin | A review on anaerobic membrane bioreactors: Applications, membrane fouling and future perspectives[END_REF][START_REF] Hai | Membrane Biological Reactors: Theory, Modeling, Design, Management and Applications to Wastewater Reuse -Second Edition[END_REF]; (3) MBRs can provide footprint savings due to a higher organic loading rate and greater reactor depth compared to CAS. Membrane fouling remains a major obstacle that hinders faster commercialization of MBRs due to its influences on flux decline, membrane lifetime span, backwash frequency, energy cost, and even permeate quality. Generally, membrane fouling in MBRs should be blamed for both membrane pore-clogging and sludge cake deposition on membranes which is usually the predominant fouling component [START_REF] Lee | Comparison of the filtration characteristics between attached and suspended growth microorganisms in submerged membrane bioreactor[END_REF]. To control fouling, aeration is effective to remove cake fouling thus enhances the membrane flux, especially for submerged membrane [START_REF] Judd | The MBR Book: Principles and Applications of Membrane Bioreactors for Water and Wastewater Treatment[END_REF][START_REF] Robles | A review on anaerobic membrane bioreactors (AnMBRs) focused on modelling and control aspects[END_REF][START_REF] Bouhabila | Fouling characterisation in membrane bioreactors[END_REF][START_REF] Verrecht | The cost of a large-scale hollow fibre MBR[END_REF][START_REF] Hong | Fouling control in activated sludge submerged hollow fiber membrane bioreactors[END_REF]. But high aeration also brings impacts on biomass characteristics, since colloids and solutes would be the major membrane foulants which cannot be removed effectively by increasing shear stress [START_REF] Fan | Interrelated effects of aeration and mixed liquor fractions on membrane fouling for submerged membrane bioreactor processes in wastewater treatment, Interrelated Eff. Aeration Mix[END_REF]. In summary, MBRs provide qualified permeate for non-potable water reuse, while improvements need to be found to decrease membrane fouling and the related energy consumptions. Moreover, the operating conditions for biological degradation and membrane purification are coupled and more difficult to control.

Anaerobic MBR (AnMBRs) are getting increasing attention and interest. Unlike MBR, AnMBR consists of a primary anaerobic bioreactor and a secondary MF/NF membrane bioreactor. First, the microorganisms in the anaerobic bioreactor convert organic carbon and BOD5 in wastewater into biogas (methane) and CO2. Second, membranes separate the microorganisms and other suspended solids from the treated effluent. The main advantage of wastewater treatment by AnMBRs is the natural aspects of the bioprocess such as the reduction of the overall energy demand, wide loading rate decreasing the need for aeration, increasing energy recovery from methane production and producing less secondary sludge [START_REF] Song | Resource recovery from wastewater by anaerobic membrane bioreactors: Opportunities and challenges[END_REF][START_REF] Harb | Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns[END_REF][START_REF] Wang | Comparison of fouling between aerobic and anaerobic MBR treating municipal wastewater[END_REF].

Once Song et al. [START_REF] Song | Resource recovery from wastewater by anaerobic membrane bioreactors: Opportunities and challenges[END_REF] tested the performance of AnMBR on synthetic domestic wastewater at the lab scale, the results showed that although the effluent after AnMBR achieved the high removal efficiency on COD (98.4 ± 0.4%), TOC (98.7 ± 0.3%) and TN (20.4 ± 11%), the quality cannot meet reuse standards due to the high concentration of COD (101.5 ± 22.9 mg•L -1 ) and TN (132.5 ± 16.9 mg•L -1 ) in the effluent. It showed the water production may contain more organic and inorganic matters from the AnMBRs than from MBRs. In addition, it has been reported that AnMBRs caused serious membrane fouling potential with high mixed liquor suspended solid (MLSS) concentration [START_REF] Wang | Comparison of fouling between aerobic and anaerobic MBR treating municipal wastewater[END_REF] and need longer biomass retention time to support the slow-growing anaerobic microorganisms than aerobic MBRs [START_REF] Le-Clech | Fouling in membrane bioreactors used in wastewater treatment[END_REF]. Therefore, further treatment process after AnMBR, such as physically adsorption, precipitation, advanced membrane filtration or disinfection, is necessary to control the fouling potential and increase the treatment efficiency of AnMBRs, when applied to water reuse processes [START_REF] Liu | Performance, membrane fouling control and cost analysis of an integrated anaerobic fixed-film MBR and reverse osmosis process for municipal wastewater reclamation to NEWater-like product water[END_REF].

In summary, UF/MF-based treatment and MBR processes can achieve non-potable applications. MBR can works as the secondary treatment in WWTPs but with high removal efficiency of contaminants. However, the fouling potential will be higher in submerged MBR than separate MF or UF due to the sludge degradation and separation and the optimization/control of operating conditions must be done simultaneously (biological and membrane processes). Consequently, for more advanced reuse applications, complementary treatments such as NF, RO or forward osmosis (FO) are often needed, and these will be the subject of the following sections. HRT: hydraulic retention time; SRT: solids retention time; nd: not detected.

NF/RO/FO-Based Treatment Processes for Water Reuse

Nanofiltration (NF) or reverse osmosis (RO) have been recognized as an effective means to provide safe and reliable source of water supplies for both potable water and non-potable water purposes [START_REF] Ang | A review on the applicability of integrated/hybrid membrane processes in water treatment and desalination plants[END_REF]. NF/RO technologies are outstanding in wastewater reuse applications, especially in potable reuse levels, because NF/RO can eliminate effectively organic micropollutants such as endocrine-disrupting compounds, pharmaceutically active compounds, pesticides, etc. [START_REF] Tepuš | Comparison between nitrate and pesticide removal from ground water using adsorbents and NF and RO membranes[END_REF][START_REF] Garcia | The application of microfiltration-reverse osmosis/nanofiltration to trace organics removal for municipal wastewater reuse[END_REF]. NF/RO processes also show significant removal efficiency on conductivity, TDS, alkalinity, salinity, hardness and ions from the feed which can be of particular interest for irrigation and potable purposes. In addition, forward osmosis (FO) is a promising membrane technology in the wastewater treatment field using a similar membrane to RO or NF membranes, but an osmotic pressure difference as a driving force [START_REF] Wang | Enhanced forward osmosis from chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membranes with a thin wall[END_REF][START_REF] Su | Cellulose acetate nanofiltration hollow fiber membranes for forward osmosis processes[END_REF][START_REF] Tang | Concentration of brine by forward osmosis: Performance and influence of membrane structure[END_REF]. Table 1-7 summarizes the NF/RO-based membrane treatment studies applied to municipal wastewater reuse and most of them using non-conventional pretreatment processes before NF/RO. The separation characteristics of NF include pore-size steric mechanism (convective flow), solution-diffusion mechanisms and electrostatic interactions [START_REF] Abdel-Fatah | Nanofiltration systems and applications in wastewater treatment: Review article[END_REF]. Dalar et al. [START_REF] Dolar | Municipal Wastewater Reclamation and Water Reuse for Irrigation by Membrane Processes[END_REF] demonstrated that the coupled MBR and NF system could remove almost all divalent and multivalent ions, such as PO4 3-and SO4 2-, but only removed less than 60% monovalent ions, such as NO3 -, Na + and Cl -. Similar results were also obtained by Bunani et al. [START_REF] Bunani | Application of nanofiltration for reuse of municipal wastewater and quality analysis of product water[END_REF]. Actually, ion rejection by NF membranes depends on the combination of electrostatic and steric interactions associated with charge shielding, Donnan exclusion and the degree of ion hydration [START_REF] Gozálvez-Zafrilla | Nanofiltration of secondary effluent for wastewater reuse in the textile industry[END_REF]. In addition, rejection mechanisms by NF highly depend on membrane properties, physicochemical properties of solutes and feed characteristics. Whereas RO was originally conceived as a method of producing potable water from the sea or brackish sources from the 1960s, the technology now is also widely applied on a large scale in municipal wastewater treatment and reuse [START_REF] Potts | A critical review of fouling of reverse osmosis membranes[END_REF][START_REF] Greenlee | Reverse osmosis desalination: Water sources, technology, and today's challenges[END_REF]. The rejection mechanism of RO includes size exclusion, charge exclusion and physical-chemical interactions between solute and solvent [START_REF] Radjenović | Rejection of pharmaceuticals in nanofiltration and reverse osmosis membrane drinking water treatment[END_REF][START_REF] Bellona | The role of membrane surface charge and solute physicochemical properties in the rejection of organic acids by NF membranes[END_REF]. RO retention capacities are better than NF due to its almost nonporous nature, reflected in higher removal of organic compounds, monovalent ions, TDS and conductivity [START_REF] Dolar | Municipal Wastewater Reclamation and Water Reuse for Irrigation by Membrane Processes[END_REF][START_REF] Jacob | Performances of RO and NF processes for wastewater reuse: Tertiary treatment after a conventional activated sludge or a membrane bioreactor[END_REF][START_REF] Uyanık | NF-RO Membrane Performance for Treating the Effluent of an Organized Industrial Zone Wastewater Treatment Plant: Effect of Different UF Types[END_REF]. As listed in Table 1-7, the conductivity removal by NF is usually effective, but not completely, ranging between 40% and 90%, while RO shows excellent separation performance on almost complete salinity removal [START_REF] Falizi | Evaluation of MBR treated industrial wastewater quality before and after desalination by NF and RO processes for agricultural reuse[END_REF][START_REF] Shanmuganathan | Experimental evaluation of microfiltration-granular activated carbon (MF-GAC)/nano filter hybrid system in high quality water reuse[END_REF]. However, it should be noted that some NF and RO membranes materials are selective in removing micropollutants probably related to their rejection mechanisms [START_REF] Silva | Micropollutant Removal from Water by Membrane and Advanced Oxidation Processes-A Review[END_REF]. For instance, the removal efficiency diminished considerably for micropollutants with a neutral or positive charge, of which the removal through RO was near 100% for naproxen, versus 20% for acetaminophen and 60% for atenolol [START_REF] Dolar | Removal of emerging contaminants from municipal wastewater with an integrated membrane system, MBR-RO[END_REF]. Forward osmosis (FO) also called as direct osmosis is a new membrane-separation process in which water moves spontaneously across a semi-permeable membrane from the feed solution (lower osmotic pressure) side to the draw solution (higher osmotic pressure) side [START_REF] Fang | Evaluation of the pore size distribution of a forward osmosis membrane in three different ways[END_REF][START_REF] Ferrari | Exploring Submerged Forward Osmosis for Water Recovery and Pre-Concentration of Wastewater before Anaerobic Digestion: A Pilot Scale Study[END_REF]. Compared to NF/RO, FO is an osmotically driven technology operated at very low or even non-hydraulic pressure during wastewater treatment [START_REF] Zou | Enhancing wastewater reuse by forward osmosis with self-diluted commercial fertilizers as draw solutes[END_REF], and FO membranes have a lower membrane fouling potential due to loose formation and less compaction of cake foulants in the absence of hydraulic pressure [START_REF] Hube | Direct membrane filtration for wastewater treatment and resource recovery: A review[END_REF]. Moreover, FO membranes present high contaminant rejection rates, high flux recovery after cleaning and high water recovery using low-grade energy resources [START_REF] Cath | Forward osmosis: Principles, applications, and recent developments[END_REF][START_REF] Volpin | Hybrid forward osmosisreverse osmosis for wastewater reuse and seawater desalination: Understanding the optimal feed solution to minimise fouling[END_REF].

However, it should be noted that when applying FO processes to wastewater treatment, further treatment such as NF, RO, MBR or membrane distillation, is required to simultaneously separate product water for reuse and recover draw solution [START_REF] Ansari | Forward osmosis as a platform for resource recovery from municipal wastewater -A critical assessment of the literature[END_REF][START_REF] Der Bruggen | Forward osmosis: understanding the hype[END_REF][START_REF] Corzo | Long-term evaluation of a forward osmosis-nanofiltration demonstration plant for wastewater reuse in agriculture[END_REF]. One of the most common combinations is the hybrid FO-RO system, in which the inlet wastewater firstly diffuses into high concentrated draw solution through the FO membrane, and then the diluted draw solution will be filtered by RO to separate water production and continuously reconstitute the draw solution [START_REF] Cath | Forward osmosis: Principles, applications, and recent developments[END_REF].

However, due to their tiny and/or nonporous characteristics, the requirements of feed water quality for NF and RO membranes are much higher than MF and UF, because even small particles such as the NOM and submicron particulates in the feed are prone to cause severe fouling problems on these membranes [START_REF] Leiknes | Removal of natural organic matter (NOM) in drinking water treatment by coagulation-microfiltration using metal membranes[END_REF][START_REF] Al-Juboori | Biofouling in RO system: Mechanisms, monitoring and controlling[END_REF]. In particular, biofouling, the irreversible adhesion on a membrane caused by microorganisms and the extracellular polymers, has been considered as the main obstacle during long term NF/RO operation [START_REF] Al-Juboori | Biofouling in RO system: Mechanisms, monitoring and controlling[END_REF][START_REF] Baker | Biofouling in membrane systems -A review[END_REF][START_REF] Kim | EPS biofouling in membrane filtration: An analytic modeling study[END_REF][START_REF] Malaeb | Reverse osmosis technology for water treatment: State of the art review[END_REF]. In order to improve filtration performance, pretreatment processes ahead of NF/RO are required to reduce the potential of fouling development [START_REF] Ang | A review on the applicability of integrated/hybrid membrane processes in water treatment and desalination plants[END_REF][START_REF] Chae | Fouling characteristics of pressurized and submerged PVDF (polyvinylidene fluoride) microfiltration membranes in a pilotscale drinking water treatment system under low and high turbidity conditions[END_REF]. Municipal wastewater treatment by hybrid pretreatment with NF/RO processes improves the produced water quality to potable reuse level.

COD: < 5 mg•L -1 F -: n.a. mg•L -1 Cl -: 63.77 mg•L -1 NO2 -: 0.3728 mg•L -1 NO3 -: 63.1 mg•L -1 PO4 3-: n.a. mg•L -1 SO4 2-: 0.464 mg•L -1
Li + : nd Na + : 38.01 mg•L -1 NH4 + : nd K + : 5.9 mg•L -1 Mg 2+ : 3.04 mg•L --1 Ca 2+ : 29.9 mg The system achieved the effective removal of bulk organic matter, nutrients and almost complete removal of all 31 trace organic contaminants investigated Not mentioned Not mentioned [START_REF] Luo | Osmotic versus conventional membrane bioreactors integrated with reverse osmosis for water reuse: Biological stability, membrane fouling, and contaminant removal[END_REF][START_REF] Luo | Evaluating ionic organic draw solutes in osmotic membrane bioreactors for water reuse[END_REF] RO MBR effluent from domestic wastewater TMP: 4-12 bars Initial Permeability: Total Estrogens:

: 6.2 L•m -2 •h - 1 •bar -1 TMP: 8 bar
: 2.4 L•m -2 •h -1 for FO Flux: 3.3 or 6.6 L•m -2 •h -1 for NF E. coli: 0 CFU•100 mL -1 TSS: < 1 mg•L -1 Turbidity: 0.22 NTU EC: 5.33 dS•m -1 SAR: 10.6 meq•L -1 B: 1.17 mg•L -1 Arsenic: 0.0015 mg•L -1 Chrome: 0.0041 mg•L -1 Copper: 0.002 mg•L -1 Manganese: 0.018 mg•L -1 Molybdenum: 0.002 mg•L -1 Nickel: 0.0016 mg•L -1 Selenium: <0.004 mg•L -1 Conductivity: 1 mS•cm -1 B: < 0.4 mg•L -1 SAR: 1.98 meq•L -1
3.6 L•m -2 •d -1 •bar -1
38 μg•L -1 Odor: 2 TSS: < 2 mg•L -1 BOD5: < 2 mg•L -1 COD: < 2 mg•L -1 TKN: 0.3-0.4 mg•L -1 Nitrate N: 0.71-1.43 mgN•L -1 TDS: 17-24 mg•L -1 pH: 5.3-5.
•L -1 Pb: 1-16 μg•L -1 Ni: 1-33.7 μg•L -1 Cu: 1-1345 μg•L -1 Cr: 1-746 μg•L -1 TSS: <1 mg•L -1 Turbidity: 0.01-0.13 NTU COD: < 32 mg•L -1 DOC: 1.04-4.1 mg•L -1 UV254: 0.001-0.01 TN: 17-21 mg•L -1 Pb: < 1 μg•L -1 Ni: < 1 μg•L -1 Cu: < 1 μg•L -1 Cr: < 1 μg•L -1
Not mentioned Not mentioned [START_REF] Dialynas | Integration of a membrane bioreactor coupled with reverse osmosis for advanced treatment of municipal wastewater[END_REF] AnMBR+RO (lab scale)

Synthetic municipal wastewater

Flux:

20 L•m -2 •h -1 COD: 400 mg•L -1 NH4 + -N: 45 mg•L -1 PO4 3--P: 5 mg•L -1 NaHCO3: 500 mg•L -1 CaCl2•2H2O: 45 mg•L -1 MgSO4•7H2O: 20 mg•L -1 FeSO4•7H2O: 20 mg•L -1 FeCl3•7H2O: 1.5 mg•L -1 NH4 + -N: 2.1 mg•L -1 PO4 3--P: 0.03 mg•L -1 TOC: 0.13 mg•L -1 Sodium: 3.2 mg•L -1 Calcium: 0.05 mg•L -1 Iron: < 0.005 mg•L -1 Chloride: 4.7 mg•L -1 Sulfate: 0.5 mg•L -1
Discharge to reservoirs for indirectly potable reuse Guidelines for NEWater in Singapore [START_REF] Gu | An innovative anaerobic MBR-reverse osmosis-ion exchange process for energy-efficient reclamation of municipal wastewater to NEWater-like product water[END_REF] NF-MBR+RO Municipal wastewater

NF: 200-300 Da Flux: 10 L•m -2 •h -1 MLSS: 513 ± 96 mg•L -1
COD: 389.8 ± 169.9 mg•L -1 DOC: 48.3 ± 13.9 mg•L -1

Ca 2+ : 28.9 ± 3.5 Mg 2+ : 7.9 ± 1.2 mg•L -1 Na + : 105.2 ± 6.9 mg•L -1 TN: 40.7 ± 6.1 NH4-N: 40.9 ± 4.5 mg•L -1 NH3-N: nd PO4 3-: 23.6 ± 3.2 mg•L -1 EC: 859.5 ± 18.9 mS•cm -1 NF permeate: COD: 99.6 ± 0.8% DOC: 0.5-2.5 mg•L -1 , 97.5% ± 1.8% Biopolymer: nd Humic substances: 0.1 mg•L -1

Not mentioned Not mentioned [START_REF] Tay | The feasibility of nanofiltration membrane bioreactor (NF-MBR)+reverse osmosis (RO) process for water reclamation: Comparison with ultrafiltration membrane bioreactor (UF-MBR)+RO process[END_REF] SAR: sodium adsorption ratio; PPCPs: pharmaceuticals and personal care products; TKN: total Kjeldahl nitrogen; FAO: Food and Agriculture Organization; TrOCs: trace organic contaminants.

For instance, the hybrid MBR with NF or RO treatment system could both significantly remove all organic compounds investigated in this study with over 95% removal efficiency for all, thus producing an adequate permeate for indirect drinking water reuse [START_REF] Alturki | Combining MBR and NF/RO membrane filtration for the removal of trace organics in indirect potable water reuse applications[END_REF]. The combination of AnMBR and RO systems could also achieve water reuse with direct energy recovery from municipal wastewater with minimized sludge production and significant energy savings [START_REF] Liu | Performance, membrane fouling control and cost analysis of an integrated anaerobic fixed-film MBR and reverse osmosis process for municipal wastewater reclamation to NEWater-like product water[END_REF][START_REF] Gu | An innovative anaerobic MBR-reverse osmosis-ion exchange process for energy-efficient reclamation of municipal wastewater to NEWater-like product water[END_REF].

In summary, NF/RO processes are usually used for higher level of water quality demand, such as potable water reuse. NF/RO has excellent removal capacity on removal of macro and micro components in wastewater, but the operation, maintenance and cleaning of membranes are more complicated and expensive which are not favorable for companies or industries.

Although FO is developing fast recently, there are not many related reports and cases on the application of municipal wastewater treatment and reuse, and it usually needs a co-treatment process such as NF or RO which in turns increases the difficulty of realization. Therefore, the choice of membrane system should be based on feed water quality and its application purpose to forego unnecessary expenses. When the reuse level is not as high as potable reuse, it is not recommended to use NF/FO/RO processes, UF-based treatment process is more likely to be chosen.

Water Recovery and Energy Consumption of Membrane-Bases Processes for Water Reuse

The desired goal of researchers and companies on wastewater treatment for water reuse is to maximize economic benefits and provide optimum parameters for long term stable operation during membrane filtration. Although many articles are published in the field of municipal wastewater reuse, most of them focus on the feasibility and innovation of the processes, the hydraulic performance, the removal efficiency and optimization of the processes. Less are focused on the real productivity, wastewater recovery rate, energy consumption or total cost during long term operations. Among all the references mentioned in the above tables of this work, only a few of them stated the relevant energy consumption, mostly estimated in pilot scales (Table 12345678). The water recovery rate from wastewater by membrane-based technologies may be influenced by feed water characteristics, the permeate consumption by physical and chemical cleaning and filtration time, etc. The net energy consumption may depend on the treatment technologies, the chemical reagents consumption and other supplementary energy production (e.g., methane), etc.

From Table 1-8, low-pressure driven membrane technologies (MF, UF, MBR) support higher productivity per unit area and present higher water recovery, over 85%. The water recovery for high-pressure driven membranes (NF, RO) and FO are relatively lower. Generally, the water recovery by RO itself only ranges from 50-75% because of the highly increased osmotic pressure during filtration [START_REF]RO reject recovery[END_REF]. In net energy comparison, low-pressure driven membrane technologies always have lower energy consumption. According to Atanasova et al. [START_REF] Atanasova | Optimized MBR for greywater reuse systems in hotel facilities[END_REF], with an inlet flowrate to an MBR over 15 m 3 •d -1 , the net energy consumption was less than 0.5 kWh m -3 , even including the cost of disinfection. The net energy costs of an MBR on municipal wastewater treatment are relatively low ranging from 0.19 to 1.07 kWh•m -3 [START_REF] Verrecht | The cost of a large-scale hollow fibre MBR[END_REF][START_REF] Pretel | The operating cost of an anaerobic membrane bioreactor (AnMBR) treating sulphate-rich urban wastewater[END_REF].

It should be noted the above data can only be used as a reference, not as the actual energy consumption for municipal wastewater reuse treatment. In addition, the processes with NF, RO and FO directly increased the energy consumption without consideration of biogas for energy recovery (Table 12345678), because of the increased TMP, membrane maintenance, etc.

In conclusion, as seen in real cases of municipal wastewater reuse treatment, the wastewater recovery rate and net energy consumption are more likely considered as the two main factors, on the basis of meeting required reuse level, because they are important indicators to determine whether the method is cost effective or not. In the future, it could be more interesting to focus on the economic prediction of membraned-based technologies, which will be the reference for the future development of wastewater reuse field.

Summary about membrane-based processes for water reuse

This above state of art gives a comprehensive insight on the global water reuse situation, reuse regulation and membraned-based treatment performance on wastewater reuse. The advantages and limitations of them on reuse purposes, are listed in Table 1-9 Membrane separation processes provide superior quality to the treated wastewater to meet local reuse guidelines. As the legal national French context is not favorable to potable reuse, it was chosen to focus on non-potable reuse in this work and so advanced treatment such as NF, RO or FO will not be studied. In summary, UF-based membrane treatment and MBRs are both efficient approaches for non-potable reuses. Considering the state of art and the local context of wastewater management of this PhD, it was chosen to focus on UF as tertiary treatment after conventional activated sludge treatment. Indeed, UF can directly filtrate the secondary effluent without change of local WWTPs designs. Therefore, this Ph.D. work will focus on the performances and sustainability of UF membrane as the main urban wastewater tertiary treatment for water reuse applications. To be sustainable, the process needs optimized operating conditions including efficient backwash procedures which will be the topic of the next section.

GAC + MF 30 L•m -2 •h -1 98% [122] UF (pilot plant, 2 years) < 0.7 m 3 •h -1 17-22 L•m -2 •h -1 [103]
UF (pilot plant, two months)

7.7-9.0 m 3 •h -1 330-380 L•m -2 •h -1 82.3-96.5% [98] UF 1.0 m 3 •h -1 28.5 L•m -2 •h -1
About 85% [START_REF] Gómez | A comparative study of tertiary wastewater treatment by physico-chemical-UV process and macrofiltration-ultrafiltration technologies[END_REF] FO + NF 0.16 (FO) and 0.187-0.35 (NF)

m 3 •h -1 FO: 2.4 L•m -2 •h -1 ; NF: 3.3 or 6.6 L•m -2 •h -1 3.44-4.57 kWh •m -3 [184] RO 0.79 m 3 •h -1 65-75% (RO itself) [134] RO 0.04 m 3 •h -1 50% (RO itself) [194] NF-MBR + RO MBR permeate flux: 10 L•m -2 •h -1 ; RO permeate flux: 20 L•m -2 •h -1 90% 0.739 kWh•m -3 [196] UF-MBR + RO MBR permeate flux: 10 L•m -2 •h -1 ; RO permeate flux: 20 L•m -2 •h -1 75% 0.732 kWh•m -3 [196] MBR + RO 0.518 kWh •m -3 [153] AnMBR + RO AnMBR permeate flux: 10-20 L•m -2 •h -1 RO permeate flux: 20 L•m -2 •h -1 RO: 75% (RO itself) 0.333 kWh•m -3
(consider energy recovery with methane) [START_REF] Liu | Performance, membrane fouling control and cost analysis of an integrated anaerobic fixed-film MBR and reverse osmosis process for municipal wastewater reclamation to NEWater-like product water[END_REF] Table 1-9 Advantages and disadvantages of various membrane-based treatment processes.

Treatment processes

Reuse level Advantages Disadvantages

MF/UFbased treatment

Non-potable reuse: toilet flushing, urban uses, irrigation, etc.

• Low-pressure driven process, high flux and high permeability.

• Low energy cost • Effective removal of high molecular weight matters, bacteria and viruses.

• UF can almost eliminate all the bacteria, protozoa and viruses, compared to MF.

• MF/UF membranes pretreated with physical/chemical process results in low fouling potential, long term operation and higher load rate.

• Health risks potential for humans.

• Incomplete removal of low molecular weight matters, dissolved organics, salinity and micropollutants, etc.

• Fouling potential

MBRs

Non-potable reuse: Toilet flushing, cleaning, process water, urban uses, irrigation, etc.

• Low-pressure driven process, high flux and high permeability.

• Low energy cost • Effective removal of organics, TSS, nutrients like N, P, S in various forms, surfactants and micropollutants from various wastewater with biologic process.

• Less organic foulants on the membrane, smaller footprint, faster plant activation, no biologic sedimentation units and less sludge production compared to CAS process.

• Particularly, AnMBRs hold significant potential to reduce the overall energy demand, together with resource recovery

• Health risks potential for humans.

• Incomplete removal of low molecular weight matters, dissolved organics, salinity and micropollutants, etc.

• Fouling potential with membrane pore-clogging and sludge cake deposition

NF/RObased treatment

Non-potable and potable reuse: agricultural irrigation, groundwater recharge, indirect potable water, etc.

• High removal efficiency of micropollutants, microorganisms and salinity, EC, other dissolved organic and inorganic matters.

• Reduce human health concerns • High level of reuse applications

• High-pressure driven process, with low flux and low permeability.

• High energy cost.

• Pretreatment demand • Biofouling caused by microorganisms.

FO-based treatment

Non-potable and potable reuse: agricultural irrigation, groundwater recharge, indirect potable water, etc.

• FO: non external pressure driven process • Lower membrane fouling potential than RO due to less formation and compaction of cake layers on FO membranes in the absence of hydraulic pressure • High flux recovery after cleaning and high water recovery using low-grade energy resources • Combination of municipal wastewater treatment with seawater desalination

• FO is a process of dilution, which needs further separation treatment.

• High requirements for the selection of draw solution and membrane material

UF membrane fouling control and management by different types of backwashes

While the optimization of UF operating parameters can control membrane fouling, membrane cleaning is more important on the fouling removal. Physical cleanings such as classic backwash (CB) and air assisted backwash (AB) are commonly used methods in membrane fouling control [START_REF] Chang | Hydraulic backwashing for low-pressure membranes in drinking water treatment: A review[END_REF]. CB can loosen and detach fouling cake partially from membrane surface, and AB is a more effective anti-fouling method compared to CB [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF][START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF][START_REF] Li | Ultrafiltration Fouling: Impact of Backwash Frequency and Air Sparging[END_REF]. Normally, AB can be operated either by air sparing in backwash water, or by air injection into membranes fibres. However, physical backwash is mostly powerless on irreversible fouling removal during long term filtration, and the residual foulants after backwashes would be recompressed after multi-cycle filtration [START_REF] Judd | The MBR Book: Principles and Applications of Membrane Bioreactors for Water and Wastewater Treatment[END_REF]. The conventional chemical cleaning plays an important role on irreversible fouling separation by chemical reagents soaking/reacting with membrane fouling which can damage the foulant-foulant and membrane-foulant interactions [START_REF] Li | Organic Fouling and Chemical Cleaning of Nanofiltration Membranes: Measurements and Mechanisms[END_REF]. However, using of high concentrated acids, soda, and/or oxidants/disinfectants and longer soaking time will cause irreversible damages gradually on membrane properties and filtration performances in long-term operation [START_REF] Shi | Fouling and cleaning of ultrafiltration membranes: A review[END_REF][START_REF] Regula | Chemical cleaning/disinfection and ageing of organic UF membranes: A review[END_REF][START_REF] Meng | Fouling in membrane bioreactors: An updated review[END_REF]. In this case, two new concept appear as promoter (i) an air injection before classical backwash to strongly reduce the fouling and to destroy organic matter [START_REF] Cordier | Ultrafiltration for environment safety in shellfish production: Removal of oyster gametes in hatchery effluents[END_REF][START_REF] Cordier | Ultrafiltration: A solution to recycle the breeding waters in shellfish production[END_REF][START_REF] Cordier | Optimization of Air Backwash Frequency during the Ultrafiltration of Seawater[END_REF] and (ii) a chemically assisted maintenance backwash, the combined physical backwash with lower concentrated oxidants/disinfectants (compared to chemical cleaning) in backwash water, has been developed

for permeability maintenance improvement recently, so as to reduce the need for intensive chemical cleanings [START_REF] Wang | Optimisation and performance of NaOCl -assisted maintenance cleaning for fouling control in membrane bioreactors[END_REF][START_REF] Yue | Membrane fouling mitigation by NaOCl -assisted backwash in anaerobic ceramic membrane bioreactors for the treatment of domestic wastewater[END_REF].

Sodium hypochlorite (NaOCl) unproperly often called "chlorine" is one of the commonly used oxidants/disinfectants, which can inactivate the microorganisms and oxidize the organic foulants to be more hydrophilic and easier to detach from the membrane surfaces [START_REF] Shao | Biofouling in ultrafiltration process for drinking water treatment and its control by chlorinated-water and pure water backwashing[END_REF][START_REF] Weerasekara | Biofouling control: Bacterial quorum quenching versus chlorination in membrane bioreactors[END_REF][START_REF] Yu | Pre-treatment for ultrafiltration: effect of prechlorination on membrane fouling[END_REF]. Studies have also found that the presence of ClO -is effective in terms of extracellular polymeric substances (EPS) disruption and microbial cell damage [START_REF] Luo | Distinct effects of hypochlorite types on the reduction of antibiotic resistance genes during waste activated sludge fermentation: Insights of bacterial community, cellular activity, and genetic expression[END_REF]. Researchers usually use the concentration total chlorine or free chlorine to illustrate the quantity of chlorine they add in solutions. Free chlorine is the amount of chlorine that is able to sanitize contaminants. Besides, combined chlorine refers to chlorine that has combined directly with the contaminants to intermediate breakdown products.

Total chlorine is basically the sum of free chlorine and combined chlorine [START_REF] Sensorex | Free Chlorine vs Total Chlorine: What's the Difference?[END_REF]. In this study, the commonly mentioned chlorine concentration refers to total concentration unless otherwise specified as free chlorine. NaOCl is an oxidant which is unstable under atmosphere with high temperature, light, strong acid, or other reductants. NaOCl is also a strong base and weak acid salt that can hydrolyze and produce HOCl, NaOCl + H2O → Na + + HOCl + OH -. The microbicidal activity of chlorine is largely attributed to undissociated HOCl. The dissociation of HOCI to the less microbicidal form (OCl -) depends on pH. The disinfecting efficacy of chlorine decreases with increasing pH, which is parallel to the conversion of undissociated HOCI to OCl - [START_REF] Block | Disinfection, sterilization, and preservation[END_REF][START_REF] Rutala | Guideline for Disinfection and Sterilization in Healthcare Facilities[END_REF].

Fukuzaki et al. [START_REF] Fukuzaki | Effect of pH on the Efficacy of Sodium Hypochlorite Solution as Cleaning and Bactericidal Agents[END_REF] reported that the bactericidal activity of 2.38 mg Cl2•L -1 (free chlorine) NaOCl was increased with pH decreasing from 9.3 to 5.7 because the HOCl amount was increased from 13% (pH 9.3) to 98% (pH 5.7). In conventional chemical cleanings, NaOCl is usually used at high levels (300-3000 mg NaOCl •L -1 / 286-2860 mg Cl2•L -1 ) and in long time soaking for powerful membrane permeability recovery and irreversible fouling removal [START_REF] Wang | Optimisation and performance of NaOCl -assisted maintenance cleaning for fouling control in membrane bioreactors[END_REF][START_REF] Wei | Critical flux and chemical cleaning-in-place during the long-term operation of a pilot-scale submerged membrane bioreactor for municipal wastewater treatment[END_REF][START_REF] Zhai | Sodium hypochlorite assisted membrane cleaning: Alterations in the characteristics of organic foulants and membrane permeability[END_REF]. However, high dosage of NaOCl will accelerate the adversely effects on membrane properties and performance [START_REF] Zhai | Sodium hypochlorite assisted membrane cleaning: Alterations in the characteristics of organic foulants and membrane permeability[END_REF], by-products formation, and higher operating costs [START_REF] Shi | Ultrafiltration of oil-in-water emulsions using ceramic membrane: Roles played by stabilized surfactants[END_REF][START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF]. Normally, the accumulated amount of NaOCl in contact with membranes can be expressed as a total dose calculated in total chlorine concentration multiplied by contact time (CT) which can provide reference for the degradation progress of membranes. Hanafi et al. reported HClO and •OH are the responsible species for the chain-scission of polysulfone, polyamide, polyethersulfone (PES) membranes [START_REF] Hanafi | Electrokinetic analysis of PES/PVP membranes aged by sodium hypochlorite solutions at different pH[END_REF][START_REF] Regula | Ageing of ultrafiltration membranes in contact with sodium hypochlorite and commercial oxidant: Experimental designs as a new ageing protocol[END_REF][START_REF] Rouaix | Experimental study of the effects of hypochlorite on polysulfone membrane properties[END_REF][START_REF] Gabelich | Enhanced oxidation of polyamide membranes using monochloramine and ferrous iron[END_REF]. Therefore, the accumulated amount of NaOCl in membrane can cause degradation of membrane materials and membrane aging. PES membranes are considered highly tolerant to oxidants [START_REF] Arkhangelsky | Impact of chemical cleaning on properties and functioning of polyethersulfone membranes[END_REF]. Wienk et al. [START_REF] Wienk | Chemical treatment of membranes of a polymer blend: Mechanism of the reaction of hypochlorite with poly(vinyl pyrrolidone)[END_REF] detected the aging of PES/PVP membrane under exposure to 6000 mg•L -1 •day of NaOCl (approximately equal to 5718 mg Cl2•L -1 •day).. Yadav et al. [START_REF] Yadav | Effects of hypochlorite treatment on the surface morphology and mechanical properties of polyethersulfone ultrafiltration membranes[END_REF] observed the PES membrane surface damage under exposure to 10 000-25 000 mg•L -1 •day of NaOCl (approximately equal to 9530-23853 mg Cl2•L -1 •day), and the damage become worse with increasing amount of NaOCl under the same conditions. While ultrafiltration is mechanically and chemically stressed, the combined oxidant with physical backwash may accelerate physical damage and/or chemical degradation of membrane materials [START_REF] Fu | Chemical aging and impacts on hydrophilic and hydrophobic polyether sulfone (PES) membrane filtration performances[END_REF]. According to Fukuzaki et al. [START_REF] Fukuzaki | Mechanisms of Actions of Sodium Hypochlorite in Cleaning and Disinfection Processes[END_REF], low concentrations of OCl -could destruct the exoplasmic organic matrix, while high concentrations of OCl -led to diffusions of OCl -into cells and disruption of cell metabolisms.

Therefore, the new chemically assisted maintenance backwash firstly proposed by Wang et al. [START_REF] Wang | Optimisation and performance of NaOCl -assisted maintenance cleaning for fouling control in membrane bioreactors[END_REF] with low dose of chlorinated disinfectants was developed and investigated on membrane cleaning efficiency. The effectiveness of the combined backwash with low dosage (<300 mg•L -1 )

of NaOCl on membrane fouling removal has been mentioned in several publications (Table 12345678910).

Some studies used to add low level of NaOCl into backwash water for disinfection but without special research on the impact of NaOCl addition on cleaning efficiency, such as Wang et al. [START_REF] Wang | Effects of operational conditions on ultrafiltration membrane fouling[END_REF],

and Liu et al. [START_REF] Liu | Chemical cleaning of ultrafiltration membranes for polymer-flooding wastewater treatment: Efficiency and molecular mechanisms[END_REF]. In 2001, Decarolis et al. [START_REF] Decarolis | Fouling behavior of a pilot scale inside-out hollow fiber UF membrane during dead-end filtration of tertiary wastewater[END_REF] demonstrated that backwashing with chlorine addition significantly improved UF membrane productivity. Afterwards, Wang et al. [START_REF] Wang | Optimisation and performance of NaOCl -assisted maintenance cleaning for fouling control in membrane bioreactors[END_REF] investigated the impacts of NaOCl-assisted backwash on the hydraulic filtration performances of membrane bioreactor (MBR) under different NaOCl loads. Yue et al. [START_REF] Yue | Membrane fouling mitigation by NaOCl -assisted backwash in anaerobic ceramic membrane bioreactors for the treatment of domestic wastewater[END_REF] did a same study scheme as Wang et al. [START_REF] Wang | Optimisation and performance of NaOCl -assisted maintenance cleaning for fouling control in membrane bioreactors[END_REF] but with a different bioreactor which was anaerobic ceramic membrane bioreactor. In result, they both confirmed that backwash with low dosage of NaOCl enhanced the organic foulant degradation and inhibited microbial regrowth on membranes. Wang et al. [START_REF] Wang | Optimisation and performance of NaOCl -assisted maintenance cleaning for fouling control in membrane bioreactors[END_REF] also mentioned that the NaOCl-assisted backwash at lower NaOCl concentrations and higher backflush frequencies made less adverse effects on the functional groups of the active layer of the membranes. Besides, Zhang et al. [START_REF]Chemical cleaning of fouled PVC membrane during ultrafiltration of algal-rich water[END_REF] stated that 95.3 mg Cl2•L -1 NaOCl solution exhibited the best performance in removing the irreversible fouling resistance (88.4% ± 1.1%) from the algalfouled UF membrane, compared to the solutions with 500 mg•L -1 NaOH, 500 mg•L -1 HCl and 150 mg•L -1 ethylene diamine tetra acetic acid. This might be attributed to the fact that NaOCl could eliminate major foulants such as carbohydrate-like and protein-like materials on the membrane surface. In result, the cases in Table 1-10 confirmed the cleaning effectiveness of disinfectants (mostly NaOCl) addition in backwash, but their concentrations varied under different conditions.

The membrane fouling strategies fed by municipal secondary effluent includes organic fouling, inorganic fouling, and microbial fouling [START_REF] Shi | Fouling and cleaning of ultrafiltration membranes: A review[END_REF][START_REF] Chen | Optimization of membrane physical and chemical cleaning by a statistically designed approach[END_REF][START_REF] Nguyen | Chemical cleaning of ultrafiltration membrane fouled by an activated sludge effluent[END_REF]. Organic fouling is the main cause of irreversible fouling for membranes. Nonetheless, the efficiency and practicality of NaOCl-assisted backwash has not been studied in real UF pilot scale and even less with periodic classic backwash (CB) and air backwash (AB). Therefore, this subject will investigate the influence of NaOClassisted CB and/or AB on the hydraulic filtration performance and fouling management in semiindustrial UF pilot plant. Besides, the impacts on physicochemical properties of membrane material under different addition frequency of NaOCl and the performance of chlorinated CB and AB will also be discussed. • Frequent backwash with chlorine addition significantly improved membrane productivity, primarily due to enhanced foulant removal by organic oxidation and bio-growth control.

[225] NaOCl-assisted backwash

0.191 mg Cl2•L -1 (optimized) 15 min × 8.33 L•m - 2 •h -1 12h × 6 L•m -2 •h -1 Synthetic municipal wastewater MBR (0.01 μm/0.1 m 2 )
• NaOCl backflush enhanced the detachment of biopolymers from the fouled membranes, and enhanced the denitrification of MBR.

• Low level NaOCl assisted backflush has slight or few adverse effects on sludge and membranes

[23] NaOCl-assisted backwash 0.953 mg Cl2•L -1 (optimized) 30s × 30 L•m -2 •h -1 9 min × 10 L•m - 2 •h -1 Domestic wastewater anaerobic ceramic MBR (0.08 μm/0.08 m 2 )
• The biodegradability of organics in the wastewater and the microbial activities of biomass were improved with low level of NaOCl assisted backwash.

• High level of NaOCl assisted backwash deteriorated cell metabolism and led to excessive production of cell lytic products.

[24]

Backwash with chlorinated water • The use of chlorinated-water backwashing decreased the number of microorganisms in the biofouling layer, but increased the level of EPS; thus, the membrane fouling resistance decreased by 8.6%.

3 mg Cl2•L -1 2 min × 60 L•m -2 •h -1 58 min × 20 L•m - 2 •h -1
[203] NaOCl-assisted backwash 95.

3 mg Cl2•L -1 1 h soaking (TMP up to 40 kPa) × 20 L•m -2 •h -1
Algal-rich water UF (0.01 μm/0.025 m 2 )

• Among the tested cleaning reagents (NaOH, HCl, EDTA, and NaOCl), 95.3 mg Cl2•L -1 NaOCl exhibited the best performance (88.4% ± 1.1%) in removing the irreversible fouling resistance.

• The surface morphology of the fouled membrane almost recovered the original state of new membrane after cleaning with NaOCl.

[229]

NaOCl-assisted backwash (CEB)

284 mg Cl2•L -1 (optimized) 5.22 L•m -2 •h -1 - Synthetic medium contained (NH4)2SO4,
NaNO2 and some trace elements MBR (0.01 μm/0.05 m 2 )

• The best cleaning effect was evident at 284 mg Cl2•L -1 of NaOCl (optimized). [START_REF] Jiang | Effect of scrubbing by NaOCl backwashing on membrane fouling in anammox MBR[END_REF] MBR: membrane bioreactor.

The units of chlorine used in different references were all uniformed to mg Cl2•L -1 , based on the relationship between NaOCl and Cl2:

1 mg•L -1 NaOCl = 0.953 mg Cl2•L -1 .

Thesis statement

This Ph.D. work is aimed to assess the performances of a semi-industrial UF pilot plant as urban wastewater tertiary treatment for water reuse, especially on best filtration conditions, water quality including microplastic particles removal by UF, and membrane fouling control and management. The flow chart of the technical strategy points for this dissertation is given in Appendix Ⅰ.

According to Chapter 1, UF appears to be an effective technology for tertiary treatment with the objective of reusing water. Although UF has already been studied in the wastewater reuse field in various regions and showed good potentiality, there are still some problems that need to be explored and improved in order to be widely used.

This thesis focused on the following issues:

1) Most publications are experimented in ideal environment or lab-scale and this work will use a semi-industrial pilot plant continuously fed with real WWTP effluent. This was possible thanks to a partnership with la Société des Eaux de Marseille Métropole which gave access to a conventional WWTP in Châteauneuf-les-Martigues (13), France.

2) Few references considered the overall operating conditions (such as flux, filtration time, backwash sequence) for best performances of UF system in this specific application and this thesis will provide these optimal operating conditions including best flux, filtration time and AB frequency.

3) The water reuse standards of different regions are becoming stricter, in particular in Europe with a new regulation released in 2020 and this work will compare the UF permeate quality with this new regulation among others. It will also assess the type, size and concentration of microplastic particles in waters with a dedicated quite new technique developed by PerkinElmer. This analytical technique will be tested on wastewaters and improved in this work.

4) Membrane fouling is an evitable problem during filtration which needs to be furtherly controlled by adapted backwash strategy (combination of classic, air and chlorinated backwashes). In addition to optimized filtration conditions, this work will improve further the performance of UF thanks to adequate backwash strategy including chlorinated backwashes.

5) This subject aims to make comprehensive consideration of the impact conditions on UF system in order to achieve the most economical and efficient operation effect and qualified water production and thus brief calculations of total costs at semi-industrial scale will be provided.

CHAPTER 2. Materials and Methods

Feed water quality

The feed water used both for lab-scale and semi-industrial-scale experiments is the secondary effluent of a municipal wastewater treatment plant (WWTP) located in Châteauneuf-les-Martigues (13), France. The WWTP was started from 2002, it uses a conventional activated sludge process followed by sedimentation tanks to treat raw wastewater. The treatment capacity of the station is 16 000 inhabitant equivalents, of which the treatment capacity is 3 200 m 3 •d -1 , and the average flow rate is 133

m 3 •h -1 .
The WWTP is in long-term stable operation, the secondary treated effluent can be discharged without risk into the natural environment.

Lab-scale filtration equipment

In order to choose a suitable UF membrane for this project in the pilot-scale, which will The membrane module used for the filtration purpose is an ALTEON TM I (Aquasource) multichannel hollow fiber UF module. Table 2-

Membrane cleaning

The review by Chang et al. (2017) [START_REF] Chang | Hydraulic backwashing for low-pressure membranes in drinking water treatment: A review[END_REF] critically addressed the critical function and parameters of backwashing on low pressure-driven membranes (mainly MF/UF) in drinking water treatment, and pointed out the optimal range of parameters that affecting the backwash performance. The main difference in our test is using low pressure-driven membrane-UF to treat secondary WWTP effluent for reuse, instead of for drinking water treatment. The parameters of classic backwash in this study were shown in Table 2-4. (1) Classical backwashes (CB) use permeate as backwash water with a flow rate of 2.5 m 3 •h -1 . The backwash water velocity is 0.64 m•s -1 . When using CB without chlorine, the backwash water for membrane heads cleaning is pumped from T2 without chlorine, when using CB with chlorine, the backwash water is pumped from T1 with chlorine. The duration and the volume of water used during a CB is respectively 52 s and 36 L.

(2) Air backwashes (AB) consists of 3 steps: 1. emptying the fibers by opening all the valves of the membrane module; 2. air injection into membrane to dry the fouling layer until reaching a pressure of 0.3 bar. The air is supplied with an air compressor and purified. The air velocity during injection is around 0.6 m•s -1 . 3. backwash at the top, bottom, and both heads with permeate with or without chlorine. This type of backwash was described by Cordier et al. [START_REF] Cordier | Ultrafiltration for environment safety in shellfish production: Removal of oyster gametes in hatchery effluents[END_REF][START_REF] Cordier | Air Backwash Efficiency on Organic Fouling of UF Membranes Applied to Shellfish Hatchery Effluents[END_REF]. In chapter 3, AB added 5 mg Cl2•L -1 of NaOCl in permeate for backwash, the duration and the volume of water used is respectively 67 s and 52 L. In chapter 5, AB adds different concentration of NaOCl (10 mg Cl2•L -1 ) in backwash water, the duration and the volume of water used is respectively 67 s and 36L. Similarly, when using AB without chlorine, the backwash water for membrane heads cleaning is pumped from T2 without chlorine, when using CB with chlorine, the backwash water is pumped from T1 with chlorine.

(3) Finally, before starting with new operating conditions or if the permeability In addition of the above-mentioned backwashes to remove membrane fouling, a flush was operated at the middle of each filtration step for about 10 s allowing feed water to circulate in the membrane in bottom-up-outside mode with flow rate between 2.0 m 3 •h -1 and 3.0 m 3 •h -1 (corresponding to ) The flush, sometimes called "rinsing", has been proved to be efficient in preventing particle deposition on membrane through circulating concentrate out with potential fouling materials in dispersed phase [START_REF] Bessiere | Low fouling conditions in dead-end filtration: Evidence for a critical filtered volume and interpretation using critical osmotic pressure[END_REF]. In result, the cooperation of flush and backwash could finally slow down fouling velocity, increase permeability, and reduce energy consumption [START_REF] Bessiere | Coupling air-assisted backwash and rinsing steps: a new way to improve ultrafiltration process operation for inside-out hollow fibre modules[END_REF].

dropped below 200 L•m -2 •h -1 •bar -1 at

Filtration conditions

In chapter 3, the experiments were all operated in automatic mode, in dead-end filtration mode at constant flux ranging from 20 to 100 L•h -1 •m -2 . Dead-end ultrafiltration (UF) has been considered as a more energy efficient operation mode compared to cross-flow filtration in large-scale water treatment systems [START_REF] Chew | Advanced process control for ultrafiltration membrane water treatment system[END_REF]. For several months of operation, filtration parameters including feed turbidity, feed temperature, flux, transmembrane pressure, calculated permeability at 20℃ were monitored continuously to investigate the impact of filtration cycle time, backwash sequence and constant flux on membrane hydraulic performances. The backwash sequence, represented by "BW 1/n" in the following contents, such as 1/3, 1/4, 1/6, and 1/9, represents n times of classic backwashes (CB) followed with 1 air backwash (AB). Different designed conditions mainly focused on filtration cycle time, filtration flux, and backwash sequence were studied in this test, as shown in Table 2- In this manuscript, the units are not those of the international system, but the practical units measured on the pilot and used by industrials.

As the flux J is constant in the semi-industrial system, the relationship between J

(L•m -2 •h -1 ) and Lp (L•m -2 •h -1 •bar -1
) can be expressed as Eq. ( 1).

𝐿𝑝 = 𝐽 𝑇𝑀𝑃 (1)
The pressure difference over a membrane is called the Transmembrane Pressure (TMP), unit bar, which is calculated by Eq. ( 2)

𝑇𝑀𝑃 = 𝑃 𝑡𝑜𝑝 ℎ𝑒𝑎𝑑 + 𝑃 𝑏𝑜𝑡𝑡𝑜𝑚 ℎ𝑒𝑎𝑑 2 -𝑃 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 (2)
Permeability recovery:

The cleaning efficiency (%) of CEB can be reflected by recovery of permeability and defined as Eq. ( 3):

𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦 = 𝐿𝑝 𝐴𝑓𝑡𝑒𝑟 𝐿𝑝 𝐵𝑒𝑓𝑜𝑟𝑒 × 100% (3)
where LpBefore and LpAfter are the membrane permeabilities recovered before and after the CEB cleaning.

Fouling resistances

According to Darcy's law [START_REF] Wiesner | Mass transport and permeate flux and fouling in pressure-driven process[END_REF], hydraulic resistance of the fouled membrane was measured with Eq. ( 4):

𝑅 𝑡 = 𝑅 𝑖𝑟𝑟 + 𝑅 𝑟𝑒 +𝑅 𝑚 = 𝑇𝑀𝑃 𝜇•𝐽 = 1 𝜇•𝐿𝑝 (4)
where, TMP is the transmembrane pressure, μ is the viscosity of permeate and J is the applied flux. Actually, the total membrane resistance (Rt) which is finally calculated by viscosity (𝜇) and permeability (Lp) includes three parts of resistances: irreversible fouling resistance (Rirr) which cannot be removed by CB, reversible fouling resistance (Rre) which can be removed by CB and membrane resistance (Rm). The unit of resistances is m -1 .

The flux at 20℃ is calculated through Eq. ( 5) [START_REF] Howell | Ultrafiltration of high-viscosity solutions: Theoretical developments and experimental findings[END_REF]:

𝐽(20℃) = 𝜇(𝑇) 𝜇 (20)
• 𝐽(𝑇) = 𝐽(𝑇) × 𝑒 [0.0239×(20-𝑇)] (5)

In two adjacent filtration cycles, it can be considered that the composition of fouling resistance in end of cycle (n-1) is

Rend(n-1) = Rm + Rirr(n-1) + Rre(n-1) (6)
While after a CB, the total resistance in the beginning of cycle (n) is

Rini = Rm + Rirr(n-1) (7)
Through difference in Eq. ( 6) [START_REF] Yang | Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-of-the-Art and Performance Analysis[END_REF] and knowing Rm, values of Rirr and Rre in the n-1 filtration cycle can be found.

Fouling Reversibility

Filtration performance was evaluated by parameters such as backwash effectiveness (fouling reversibility), fouling rate, and fouling resistance [START_REF] Resosudarmo | Analysis of UF membrane fouling mechanisms caused by organic interactions in seawater[END_REF].

Backwash effectiveness can be indicated by fouling reversibility which was calculated after each filtration cycle n according to Chang et al. (2016) [START_REF] Chang | Hydraulic backwashing for low-pressure membranes in drinking water treatment: A review[END_REF][START_REF] Chang | Role of backwash water composition in alleviating ultrafiltration membrane fouling by sodium alginate and the effectiveness of salt backwashing[END_REF]. Reversibility after each filtration cycle could then be calculated using the initial TMP and final TMP values (𝑇𝑀𝑃 𝑒𝑛𝑑 𝑛 𝑎𝑛𝑑 𝑇𝑀𝑃 𝑖𝑛𝑖 𝑛 ) of the cycle n as well as the initial TMP of the next filtration cycle (𝑇𝑀𝑃 𝑖𝑛𝑖 (𝑛+1) ). As described above, the flux and viscosity at 20°C are both constant during each filtration condition. Therefore, the reversibility can be calculated as follow Eq. [START_REF] Shi | Role of concentration polarization in cross flow micellar enhanced ultrafiltration of cadmium with low surfactant concentration[END_REF].

𝑅𝑒𝑣𝑒𝑟𝑠𝑖𝑏𝑖𝑙𝑖𝑡𝑦(𝑛) = 𝑇𝑀𝑃 𝑒𝑛𝑑 𝑛 -𝑇𝑀𝑃 𝑖𝑛𝑖 (𝑛+1) 𝑇𝑀𝑃 𝑒𝑛𝑑 𝑛 -𝑇𝑀𝑃 𝑖𝑛𝑖 𝑛 = 𝑅 𝑒𝑛𝑑 𝑛 -𝑅 𝑖𝑛𝑖 (𝑛+1) 𝑅 𝑒𝑛𝑑 𝑛 -𝑅 𝑖𝑛𝑖 𝑛 (8)
During one operating condition, there were multiple CBs and ABs. For each condition, a mean value of CB reversibility and AB reversibility, with the related standard deviation were calculated. In chapter 5, statistical analysis was performed to determine if there was a statistically significant linear regression between backwash reversibility and Rirr before backwash. The data were analysed by XLSTAT (Addinsoft), and an ANOVA test was performed.

Water recovery rate

The recovery rate represents the proportion of net produced water quantity when compared to the total inlet feed water quantity. This was calculated with Eq. [START_REF] Shi | Ultrafiltration of oil-in-water emulsions using ceramic membrane: Roles played by stabilized surfactants[END_REF].

𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 𝑟𝑎𝑡𝑒 = 𝑉 𝑛𝑒𝑡 𝑉 𝑖𝑛𝑙𝑒𝑡 𝑋 100 = 𝑉 𝑖𝑛𝑙𝑒𝑡 -𝑉 𝐶𝐵 -𝑉 𝐴𝐵 -𝑉 𝐶𝐸𝐵 -𝑉 𝐶𝑜𝑛 𝑉 𝑖𝑛𝑙𝑒𝑡 𝑋 100% (9)
where Vinlet refers to the volume of inlet feed water, Vnet refers to the net volume produced. The calculation of Vinlet is related to the filtration flux and filtration time, as in Eq (13). The volume unit is the liter.

𝑉 𝑖𝑛𝑙𝑒𝑡 = 𝐽 × 𝑡 𝑓 (10)
VCon refers to the concentrate volume, which is known to be 2 L (volume of fibers presented in Table 2-3) and VCB, VAB, and VCEB represent the volume of permeate consumed for CB, AB and CEB which are 36 L, 52 L and 250 L, respectively.

Impact of air backwash on irreversible resistance increase

To find out the influence of air backwash frequency on UF membrane filtration performance, the variation of irreversible fouling during operation can be an interesting parameter to follow. The relationship of Rirr/Rm variation with feed water turbidity integration (Eq. ( 11)) will be considered to investigate the influence of backwash sequence on fouling formation as the function of the quality of feed water changes:

( 𝑅 𝑖𝑟𝑟 / 𝑅 𝑚 ) 𝑛 ( 𝑅 𝑖𝑟𝑟 / 𝑅 𝑚 ) 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 = 𝑓(∑ʃ𝑇𝑢𝑟. 𝑑𝑡) ( 11
)
where the turbidity integration with time is shown as follows with n=number of filtration cycle, and tf the duration of a filtration cycle.

∑ [∫ 𝑇𝑢𝑟𝑏𝑖𝑑𝑖𝑡𝑦. 𝑑𝑡 𝑡 𝑓 0 ] 𝑖 𝑛 𝑖=1 (12)
Obviously, the membrane fouling is not limited to the quantity of suspended matter

given by the measurement of turbidity but an order of magnitude was obtained. In fact, it was shown during this study that the variation in turbidity had a direct impact on the variation of the permeate flux. In this case, parameters such as the presence of organic matters are not considered.

Fouling removal efficiency of backwashes

In chapter 5, the removal efficiency of physical backwashes on turbidity and TOC (removal rates) are illustrated to furtherly verify the effectiveness of physical backwashes. For organic matters, the accumulation of dissolved organic matters was already integrated with filtration time by Lin et al. [START_REF] Lin | Effects of mass retention of dissolved organic matter and membrane pore size on membrane fouling and flux decline[END_REF]. Therefore, the turbidity and TOC are considered as accumulated amounts in membrane during the filtration cycles, the removal rates of these parameters can be calculated with the following equations based on the amount of substance balance.

here, V0 is the filtration volume (L) through the UF membrane during one filtration cycle.

VBW is the physical backwash volume during one physical backwash, VBW = 36 L.

J is the filtration flux, J = 60

L•h -1 •m -2 .
S is the surface area of UF membrane, S = 9 m 2 .

t is the filtration time during one filtration cycle, t = 1h. In this work, FT-IR spectroscopic imaging in reflectance mode using a focal plane array (e.g., 64 × 64 pixels) has been applied to the identification properties. This detection mode enables the rapid analysis of thick and opaque samples and are therefore highly suitable for detecting microplastics in environmental samples [START_REF] Tagg | Identification and Quantification of Microplastics in Wastewater Using Focal Plane Array-Based Reflectance Micro-FT-IR Imaging[END_REF][START_REF] Huppertsberg | Instrumental analysis of microplastics-benefits and challenges[END_REF].

Spectral resolution is a measure of how well a spectrometer can distinguish closely spaced spectral features. According the investigation on infrared spectra differences of polypropylene under different resolutions (2 cm -1 , 4 cm -1 ,6 cm -1 , 8 cm -1 , 12 cm -1 , 32 cm -1 and 64 cm -1 ) by Zheng et al. ( 2021), the 16 cm -1 spectral resolution was optimized and thus is selected in this study as the analytical devices used in both studies were the same. A background spectrum was collected for each sample from a blank area of the gold filter at a spectral resolution of 16 cm -1 with pixel size both at 6.25 μm or 25 μm.

The other identification parameters of micro-FT-IR in this study are as follows: 2 scans per pixel, an interferometer speed of 2.2 cm•s -1 , IR spectral range of 4000 cm -1 -690 cm -1 and the resolution of pixel size selected at 6.25 μm or 25 μm depending on the filters used (25 μm stainless steel filter with 25 μm, 3 μm and 5 μm gold coated filters with 6.25 μm). The scanning area ranged from 6000 μm × 6000 μm to 10000 μm × 10000 μm which were selected from the edges of the sample deposited on each filter.

For each sample, the FT-IR system will generate an absorbance image with an infrared spectrum information on each pixel.

To identify microplastics' structure easier and faster, a freeware, siMPle, developed by Aalborg University, Denmark and Alfred Wegener Institute, Germany, is adopted in this study. The reference database contains both plastic polymers and natural materials such as protein and cellulose, totally in 23 types of materials given in Table 2-8. The siMPle software is created based on the combination of MPHunter [START_REF] Liu | Microplastics in urban and highway stormwater retention ponds[END_REF] and AWI Automatic Pipeline [START_REF] Primpke | An automated approach for microplastics analysis using focal plane array (FPA) FTIR microscopy and image analysis[END_REF] for MP analysis that compares the IR-spectrum of each map pixel with the spectra of a reference database and assigns a score to the quality of each match [START_REF] Primpke | An automated approach for microplastics analysis using focal plane array (FPA) FTIR microscopy and image analysis[END_REF][START_REF] Primpke | Reference database design for the automated analysis of microplastic samples based on Fourier transform infrared (FTIR) spectroscopy[END_REF]. The parameters than can be detected from siMPle include the polymer types, range of abscissa and ordinate, numbers of pixel, minor/major dimension, surface area, and estimated volume and mass of each particle. The major dimension is analysed for the longest distance between pixels of the particle. The minor dimension is found by assuming the particle shape is an ellipse and knowing the area of the particle in the scan. After the preparation, the water samples are ready to be filtered. There are 2 types of filters used, the 3 μm gold-coated polyester membranes (i3 TrackPor P, Germany), and 25 μm stainless steel filter. In reflectance mode, the filter type needs to reflect IR radiation without any significant absorptions. Normally, the gold-coated filters show high energy in reflectance, and the stainless steel slide can reflect all infrared light without contributing to the infrared spectrum [START_REF] Gonzalez-Torres | Evaluation of biochemical algal floc properties using Reflectance Fourier-Transform Infrared Imaging[END_REF]. The samples are filtrated through a vacuum apparatus, shown in Figure 2-5. The apparatus is composed of filtering cup, filtration mask, spring clamp, filter, glass stopper, and conical flask. The filtration masks are round metal molds with hollow square in the center to regulate the area of the filters which will be analysed by FT-IR. The dimensions of the square on filtration masks are 6000 μm × 6000 μm and 10000 μm × 10000 μm, respectively. In this experiment, the mask with 6000 μm × 6000 μm square is mainly used on 3 μm gold coated filters, the mask with 10000 μm × 10000 μm square is used on 25 μm stainless steel filter. For the samples with visible particles and solids, it is better to firstly filtrate them through the 25 μm stainless steel filter, and secondly filtrate with a 3 μm gold filter and then perform the analysis of both filters to make results more reliable. For clean water samples as UF permeates, it can be directly filtrated through the 3 μm gold filter. Before and after testing on FT-IR spectroscopy, the filter with collected sample will be put in an evaporating dish to avoid external pollution. A TOC-L machine (Shimadzu, Japan) based on the 680°C combustion catalytic oxidation method was used to measure the concentration of total organic carbon (TOC).

The non-purgeable organic carbon (NPOC) method with a detection limit of 4 μg L -1 was used.

During Campaign 2, COD and BOD5 were tested by an external laboratory (Carso - [START_REF] Yang | Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-of-the-Art and Performance Analysis[END_REF]. Currently, it is logically predicted that non potable reuse is more successful to build the degree of familiarity and trust required by the public for acceptance [START_REF] Marks | Taking the public seriously: the case of potable and non potable reuse[END_REF]. In non-potable water treatment, ultrafiltration (UF) has been widely accepted as one of the most cost-effective technology to deal with secondary effluent on non-potable reuses, such as agricultural irrigation, landscape irrigation, urban reuse, car washing, and sometimes as process water for industries [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF][START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF]. UF enables high removal efficiency on total suspended solids (TSS), turbidity and to a smaller extend on total organic carbon (TOC). More importantly, UF can retain microorganisms significantly, including bacteria, protozoa, and viruses [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF]. The investigation of Muthukumaran et al. [START_REF] Muthukumaran | Performance evaluation of different ultrafiltration membranes for the reclamation and reuse of secondary effluent[END_REF], Pollice et al. [START_REF] Pollice | Tertiary filtered municipal wastewater as alternative water source in agriculture: a field investigation in Southern Italy[END_REF] and Falsanisi et al. [START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF] all confirmed that UF (with prefilter) can be successfully applied on secondary effluent treatment for reuse in agriculture with respect to WHO guidelines in terms of permeate quality. To be reliable, the three publications were all conducted in pilot-scale operation ranging from 2 months to 2 years, and with UF pore sizes ranging from 0.002μm (1kD) to 0.03μm. Additionally, both Pollice et al.

[103] and Falsanisi et al. [START_REF] Falsanisi | Ultrafiltration (UF) Pilot Plant for Municipal Wastewater Reuse in Agriculture: Impact of the Operation Mode on Process Performance[END_REF] used real secondary effluent as feed water and Muthukumaran et al.

[102] used the synthetic secondary effluent.

Nowadays, membranes are committed to combine material properties and self-forming mechanism for better filtration processes. The selection of material is affected by pore size distribution, wetting susceptibility, porosity, mechanical strength, cost, polymer flexibility, fouling resistance, stability, durability, and chemical resistance [START_REF] Bruggen | A review of pressure-driven membrane processes in wastewater treatment and drinking water production[END_REF]. Currently, polymer membranes are widely used among membranes with advantage of superior mechanical strength and low cost.

Additionally, PES is one of the most commonly used polymer material for UF and also as supporting substrates for NF and RO processes approved with excellent permeability, mechanical stability, and chemical resistance [START_REF] Lee | Membrane materials for water purification: design, development, and application[END_REF]. To find out a suitable UF membrane, the beginning of this chapter aims to investigate the secondary effluent filtration performances (including flux, fouling formation, and permeate quality) of UF at different molecular weight cut-off (MWCO) in the labscale.

In secondary wastewater treatment in full scale, a main drawback limiting the economical operation of UF process on wastewater reuse treatment is the fouling resistance, especially the irreversible fouling which is mainly deposited by the organic matters in the secondary municipal wastewater [START_REF] Zheng | Contribution of effluent organic matter (EfOM) to ultrafiltration (UF) membrane fouling: Isolation, characterization, and fouling effect of EfOM fractions[END_REF]. In general, two types of fouling phenomena are distinguished for UF membranes in secondary effluent treatment. The first type is the macro-solute or particle deposition on UF membranes mainly caused by suspended solids in feed is mostly external fouling or cake formation on the top surface of the membrane, which is usually reversible and non-adhesive [START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF]. The second type is the organic matters caused pore blocking and internal pore adsorption on UF membranes, which is usually irreversible and adhesive [START_REF] Katsoufidou | An experimental study of UF membrane fouling by humic acid and sodium alginate solutions: the effect of backwashing on flux recovery[END_REF].

In the field of fouling management, the feed water quality, and filtration conditions (filtration flux, filtration cycle time (backwash interval), and cleaning mode play important roles due to their direct effects either on the formation and nature of the fouling layer, or on the removal of the foulants. Normally, less concentration of dissolved organic matters and suspended solids is in feed water, the more beneficial it is to control fouling formation. Therefore, we use secondary treated water as the feed water and a 130 μm prefilter is set in front of UF. During filtration, the filtration flux and filtration time will be incorporated to affect the thickness and density of the foulants deposited on the membranes [START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF].To maintain a sustainable and effective treatment performance, frequent cleaning of the membranes is required including physical and chemical washing.

Chemical washing is generally applied to remove hydraulically irreversible foulants. The choice of chemical agents on membranes, mostly using acids, alkalis, or oxidants, should be based on the membrane materials and fouling types [START_REF] Shi | Fouling and cleaning of ultrafiltration membranes: A review[END_REF]. Physical cleaning like classic backwash (CB) and air assisted backwash (AB) are commonly applied in most UF process designs as standard operating strategies to limit fouling [START_REF] Chang | Hydraulic backwashing for low-pressure membranes in drinking water treatment: A review[END_REF]. Besides, forward flushing with a high flow rate of water can be incorporated with physical backwashing to decrease aggregation or dense attachment of particulates on the membrane surface [START_REF] Gao | Membrane fouling control in ultrafiltration technology for drinking water production: A review[END_REF]. CB is commonly used to loosen and detach fouling cake partially from membrane surface. In addition, air assisted backwash is accepted as a more effective anti-fouling physical cleaning compared to CB. While the CB is expected to detach the cake layer from the hollow fiber, air injection contributes to break up and detach foulants away from the membrane surface [START_REF] Bessiere | Coupling air-assisted backwash and rinsing steps: a new way to improve ultrafiltration process operation for inside-out hollow fibre modules[END_REF][START_REF] Serra | Use of air sparging to improve backwash efficiency in hollow-fiber modules[END_REF]. Normally, AB can be conducted either by air scouring in backwash water, or by air injection into membranes fibres. In air scouring process, air is injected into the membrane with the feed stream to generate a gas-liquid two-phase flow, leading to higher shear stress near the membrane surface [START_REF] Psoch | Anti-fouling application of air sparging and backflushing for MBR[END_REF]. In air injection process, air can be injected into the concentrate side (inside the lumen of the fiber) without feed stream [START_REF] Remize | Evaluation of backwash efficiency, definition of remaining fouling and characterisation of its contribution in irreversible fouling: Case of drinking water production by air-assisted ultra-filtration[END_REF]. Assisted by air scouring, a previous study by Ye et al. [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF] demonstrated the air assisted backwash system in moderate air flow rate (e.g. 154 mL•min -1 ) could remove most of the foulants more effectively while the loosen and residual foulants after classic backwash would be recompressed when filtration restarts. Air souring is more likely to be used in MBR [START_REF] Psoch | Anti-fouling application of air sparging and backflushing for MBR[END_REF][START_REF] Salerno | Influence of air scouring on the performance of a Self Forming Dynamic Membrane BioReactor (SFD MBR) for municipal wastewater treatment[END_REF]. Salerno et al. [START_REF] Salerno | Influence of air scouring on the performance of a Self Forming Dynamic Membrane BioReactor (SFD MBR) for municipal wastewater treatment[END_REF] compared air scouring with flow rate of 150, 250, and 500 mL•min -1 MBR process and concluded that the 150 mL•min -1 considered as an optimal compromise between high effluent quality and limited cleaning frequency.

Assisted by air injection, P.J. Remize et al. [START_REF] Remize | Evaluation of backwash efficiency, definition of remaining fouling and characterisation of its contribution in irreversible fouling: Case of drinking water production by air-assisted ultra-filtration[END_REF] also stated that backwash procedure was hydraulically enhanced by air which was injected into the concentrate side, the remaining particulate fouling was significantly lowered and leads to an increase in process runtime.

Additionally, C. Cordier et al. [START_REF] Cordier | Air Backwash Efficiency on Organic Fouling of UF Membranes Applied to Shellfish Hatchery Effluents[END_REF] confirmed the higher removal ability of AB with air injection, and it could destroy the cells' integrity by air injection, such as oysters' oocytes and spermatozoa in seawater. However, frequent air assisted backwash can bring some disadvantages. 1. Frequent and/or high flow rate of air scouring backwash would not remove macromolecules effectively, and in contrast might cause serious pore blocking inside membranes [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF]. 2. Because of the harsh requirement of air backwash for membranes (e.g., low bubble point and easily rewetting) [START_REF] Serra | Use of air sparging to improve backwash efficiency in hollow-fiber modules[END_REF],

air assisted backwash may lead to partial drying for certain membranes, which can cause embrittlement and membrane integrity problems [START_REF] Chang | Hydraulic backwashing for low-pressure membranes in drinking water treatment: A review[END_REF]. 3. Air assisted backwash requires more energy and equipment cost due to the requirements of air blowers, and more complex operation and maintenance of air backwash. Considering both the pros and cons of classic backwash and air assisted backwash, a strategy that maximizes benefits may corporate periodic classic backwash, and air assisted backwash together in a filtration mode (named as periodical backwash sequence in this test) to provide better fouling removal effects. Through retrieval, there are very few publications about the performance of alternative backwash and air assisted backwash during one filtration condition, nor the optimization of filtration conditions. Although C. Cordier et al. [START_REF] Cordier | Optimization of Air Backwash Frequency during the Ultrafiltration of Seawater[END_REF] has reported the several backwash sequences (1/3, 1/5, 1/7, and 1/9) with this article focused on UF membrane filtration, the test was fed with aquaculture seawater, which is different from the composition of municipal secondary effluent wastewater shown in this work.

Therefore, it is very meaningful to set-up on-site a semi-industrial UF pilot plant with periodic classic backwashes (CB) and air backwashes (AB) on real secondary effluent for water reuse application. The target of this study is to find out the optimized filtration conditions that can be long-term applied on secondary wastewater treatment for water reuse with guarantee of adequate permeate quality, sustainable hydraulic filtration performance, and high net permeate production.

15 different filtration conditions are designed to identify the effects of flux, filtration cycle time, and backwash sequences on hydraulic filtration performance. The filtration performances will be described through the analysis of fouling reversibility and composition, water recovery rate, and the impact of AB frequency on irreversible fouling control. The analysis of permeate quality will be discussed in chapter 4.

Comparison of membranes' performances in lab-scale

There are three tested ultrafiltration membranes (shown in Table 2-2) to be compared in lab, with MWCO of 30 kDa, 100k Da and 200 kDa, respectively. The tested WWTP (Châteauneuf-les-Martigues, France) effluent contained 8.9 mgC.L -1 of total organic carbon (TOC) and with mean turbidity of 3.5 NTU. The initial permeabilities at 20°C of 200, 100 and 30 kDa membranes are 960, 770 and 365 L•h -1 •m -2 •bar -1 , respectively. During filtration experiments, the transmembrane pressure (TMP) was set to 0.3 bar, and permeate samples were collected for analysis.

Flux decline

Due to concentrate volume difference on different membrane modules (i.e. geometry), Figure

Permeate quality

To compare the permeate quality from different membranes, parameters including turbidity and TOC rejection rates were tested. As a result, all membranes can decrease the turbidity from feed water to less than 0.8 NTU with more than 90% removal rates. With the extension of filtration, all the membrane showed increased turbidity retention rate which indicated that the formed cake foulant on membranes helped to hold up more contaminants in feed water. The 100 kDa hollow fiber membrane showed the highest and most stable turbidity retention rate compared to 30 kDa and 100 kDa flat sheet membranes, which resulted in > 99.9% removal of turbidity. For TOC rejection, 200 kDa hollow fiber membranes showed the highest removal efficiency with more than 95% removal rates, while the 30 kDa and 100 kDa flat sheet membranes could just remove about 40% and 50% of TOC from the feed. Here to be noted, the removal rates were calculated by the TOC concentration in permeate with the TOC concentration in the volume near the membrane. As the hollow fiber module has smaller concentrate volume (1.9 mL) than the Amicon stirred cell (420 mL), the TOC concentration in concentrate of hollow fiber module will be much higher than that in concentrate of flat sheet membrane module, this is why there is a big difference on TOC removal between the hollow fiber and flat sheet membranes. Actually, the concentration of TOC in all permeates had less difference and were all around 4~7 mg•L -1 .

Fouling resistance

To further compare, the total resistance on membrane increase on UF membranes during filtration was shown in Figure 3-2. According to Darcy'law, the intercept on Y axis represents the initial membrane resistance of each membrane, the slope of each fitted curve represents the increasing rate of total fouling resistance. Through comparison, 200kDa membrane showed the lowest fouling increasing rate during filtration, which reflects the better anti-fouling character than the others. In order to evaluate the fouling types, a backwash experiment was carried out with the hollow fiber module with 1/3 volume of total permeate under 2 bar. The results showed that the total fouling resistance was composed of 97% of reversible fouling and 3% of irreversible fouling in the lab-scale which is quite promising for full-scale experiments. and of course a large membrane specific area due to the geometry, thus it is considered to be the most adequate membrane for the semi-industrial pilot plant experiments.

Understanding of UF feed variability and potential impact on UF performance in pilotscale

Before studying the performance of the UF pilot plant, it is very important to explain the WWTP running operation (because the UF feed water is function of it). The flowrate of raw wastewater in the WWTP strongly changes continuously between day and night and the temperature too. Classically, the peak periods of residential water use all over a day generally occur at 7:00 to 10:00, 12:00 to14:00 and 18:00 to 20:00, while the trough period occurs between 0:00 to 4:00 where the flowrate is divided by a factor 20. In general, periods with higher flowrate mean higher load rate for the biological wastewater treatment processes, such as activated sludge process in the tested WWTP. According to Aygun et al. ( 2007) [START_REF] Aygun | Influence of High Organic Loading Rates on COD Removal and Sludge Production in Moving Bed Biofilm Reactor[END_REF], when increasing the organic loading rate in raw wastewater (increasing COD), the performance of treatment process became powerless thus the COD removal efficiency decreased. In addition, higher flowrates lead to reduced sedimentation times in the clarifier which can decrease the particles' removal thus increasing turbidity. This can be observed in Figure 3-3 presenting the variations of inlet secondary wastewater flowrate and outlet turbidity. Moreover, the weather, such as a rainfall may significantly increase the flowrate and change the compositions of wastewater, and thus also further affect wastewater treatment performance and effluent quality [START_REF] Rashid | Assessing environmental impacts of large centralized wastewater treatment plants with combined or separate sewer systems in dry/wet seasons by using LCA[END_REF] (i.e. feed of UF).

In order to show the influence of this feed water quality on UF performance, the variations of permeability, feed water turbidity and temperature obtained for regular days in condition J60t20BW1/3 (permeate flux of 60 L h -1 m -2 , duration of filtration step 20 min and 1 AB followed by 3 CB) are shown in Figure 3-4 and Figure 3-5. This condition is taken as a representative example of all conditions. As demonstrated by M. Raffin et al. [START_REF] Raffin | Influence of backwashing, flux and temperature on microfiltration for wastewater reuse[END_REF] and Huang et al. [START_REF] Huang | Natural organic matter fouling of low-pressure, hollow-fiber membranes: Effects of NOM source and hydrodynamic conditions[END_REF], the feed water quality was one of the main factors on membrane fouling formation, and turbidity, as an indicator of water quality, directly reflects the potential of fouling. In Figure 3-4, the membrane permeability has converse variation trends with turbidity variation. The partial increase of permeability maybe caused by the periodical variation of feed water flowrate and quality. From above, trough periods with lower turbidity of feed produced less fouling load on membrane thus the permeability decreased slower than during peak periods. Periodical backwash can remove the previous cake foulant thus improving the permeability recovery after backwash. This phenomenon may explain some significant increase of permeability during the filtration process that occurred usually at the trough periods of a day (red circles in Figure 34). Additionally, the process temperature can also affect the permeability. In this study, the filtration was conducted in constant flux mode whatever the temperature changes as shown in temperature increase [START_REF] Huisman | Water permeability in ultrafiltration and microfiltration: Viscous and electroviscous effects[END_REF], therefore, the permeability at real temperature will be in positive relationship with temperature variation based on Darcy's law. Moveover, as early as in 1880s, Tarnawski and Jelen [START_REF] Tarnawski | Estimation of compaction and fouling effects during membrane processing of cottage cheese whey[END_REF] found a non-linear permeability increase for a polymeric UF membrane in the temperature region from 20°C to 45°C even after compensating for the viscosity decrease, and they attributed this increase partly to a thermal expansion of the membrane material. Generally, the variation of UF permeability is the combined effects by many factors, such as flow velocity,

Lp@20℃(L•m -2 •h -1 •bar -1 ) & Flux (L•m -2 •h -1 ) Time(h) Lp @20 Flux at real T ℃ T/℃ ( a) ( b)

Impact of filtration time and flux on hydraulic performances in pilot scale

Overview of permeability variations with CB and AB

Each operational condition in our test (Table 23456) was carried out with sustainable filtration process for more than 40h. Before explaining in details the different results obtained, the condition J60t60BW1/3 is taken as an example (Figure 3456), to show the permeability variation curves. It is observed that the filtration system was operated in periodically backwash, with three times of CB between adjacent AB which was related to the fixed backwash sequence in each condition. The other conditions were all operated in the similar status but with different filtration conditions. If a CEB happened, the backwash sequence setting returned to the initial state. According to Figure 3-6, the permeability was partially recovered regularly by cleaning methods. In Figure 3-6 (b), a better fouling removal efficiency by AB than by CB is obtained because the initial Lp after each AB is higher than initial Lp after pervious CB.

Impact of filtration time and flux on fouling reversibility and hydraulic performances

Filtration performance was evaluated by parameters such as backwash effectiveness (fouling reversibility, Eq.8), fouling rate, and fouling resistance. Generally, the total fouling resistance in UF filtration is mainly composed of hydraulic resistance of cake resistance Rc [START_REF] Boerlage | Development of the MFI-UF in constant flux filtration[END_REF], therefore both (0.167 bar) from the beginning of the filtration process. The increase of TMP may compress the fouling layer (i.e. cake density) which will promote the smallest particles penetration into membrane pores thus enhancing irreversible fouling [START_REF] Raffin | Influence of backwashing, flux and temperature on microfiltration for wastewater reuse[END_REF][START_REF] Grandison | Hydrodynamic factors affecting flux and fouling during ultrafiltration of skimmed milk[END_REF]. In this case, although backwashes could flow away the cake foulant on membrane surface significantly, they could not remove the smallest compounds clogging into membrane effectively, thus decreasing CB and AB reversibility [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF]. As the i versible fouling is mainly caused by increased TMP, the irreversible fouling was more sensitive to flux increase than filtration cycle time extension in these tests: this is in agreement with Akhondi et al. [START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF].

In order to confirm the above results, the variations and composition of fouling resistances before backwash versus time are proposed for each condition (Figure 3456789). J60t20BW1/3, J60t60BW1/3, and J100t30BW1/3 are taken as representatives of the 3 types of conditions.

-In soft condition J60t20BW1/3, membrane resistance Rm was in dominant position during the whole filtration, and Rirr did not reach to one-third of Rm.

-In standard condition J60t60BW1/3 with 40 min filtration time longer than J60t20BW1/3 in a cycle, the irreversible fouling Rirr gradually reached the value of Rm after 35 hours of operation and stayed in the same order of magnitude than Rm.

-In harsh condition J100t30BW1/3 with the highest flux among all tested conditions, the irreversible fouling Rirr increased fastest from beginning and exceeded the value of Rm. Higher values of reversible resistances than in soft or standard conditions are also to be noted.

Through comparison, increase of flux and filtration cycle time both contribute to the increasing rate of Rirr during filtration process. The increase of filtration flux (comparison between J60t60 and J100t30) seems to have a higher impact on Rirr increasing rate than the increase of filtration time (comparison between J60t20 and J60t60).

From above, the harsh conditions all resulted in occurrence of CEB during 40 h's operation, especially in condition J100t30BW1/3 with the most frequent CEB needed. In practical uses, the CEB interval usually ranges from hours to weeks among different UF processes [START_REF]Microfiltration and Ultrafiltration Membranes for Drinking Water: M53[END_REF][START_REF]Physical Removal of Microbiological, Particulate & Organic Contaminants in Drinking Water[END_REF].

Because one CEB consumes more chemical agents, permeate water, and energy compared with an AB or a CB, it is necessary to prolong the CEB interval during filtration. It has been previously estimated that sustainable operating conditions lead to less than 2 CEB occurences per day [START_REF] Cordier | Ultrafiltration for environment safety in shellfish production: Removal of oyster gametes in hatchery effluents[END_REF][START_REF] Cordier | Air Backwash Efficiency on Organic Fouling of UF Membranes Applied to Shellfish Hatchery Effluents[END_REF]. Therefore, the harsh conditions cannot be considered as the optimized conditions for long term operation. Furthermore, the permeate water was produced for reuse, but it was also used for cleanings.

The permeate consumption in CB, AB, and CEB conversely decreased the productivity of the system. Therefore, it is necessary to investigate the water recovery rate (Eq.9) in different conditions to make a comprehensive comparison, shown in in Figure 3-10 all conditions of AB frequency of 1/3. Through calculation, the highest recovery rates occurred in the standard

Impact of air backwash frequency

Based on the above analysis, AB was definitely resullted in higher reversibility compared to CB, thus reflecting the higher removal efficiency on cake fouling. Indeed, many publications confirmed the high removal efficiency by air-assisted backwash including air drying and air scouring applied on low-pressure driven membranes [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF][START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF][START_REF] Li | Ultrafiltration Fouling: Impact of Backwash Frequency and Air Sparging[END_REF][START_REF] Bessiere | Coupling air-assisted backwash and rinsing steps: a new way to improve ultrafiltration process operation for inside-out hollow fibre modules[END_REF][START_REF] Serra | Use of air sparging to improve backwash efficiency in hollow-fiber modules[END_REF][START_REF] Guigui | Air sparging backwash in ultrafiltration hollow fibres for drinking water production[END_REF][START_REF] Lipp | Application of out-in MF/UF-systems for drinking water treatment with air supported backwashthree case studies[END_REF]. To evaluate the impact of AB frequency on filtration performance and confirm that the frequencies 1/3 and 1/4 previously studied were the best, 5 different backwash frequencies (1/3, 1/4, 1/6, 1/9, and No AB) (Table 23456) were tested, all under the constant flux and filtration cycle time (J = 60 L•m -2 •h -1 and t = 60 min). The variation of (Rirr/Rm)n/(Rirr/Rm)ini versus turbidity integration based on Eq. [START_REF]Guidelines for the safe use of wastewater, excreta and greywater[END_REF] and Eq. ( 12) reflecting the Rirr increasing rate was calculated and is shown in Figure 3-11. The turbidity integration enables to consider feed water quality variation over time considering turbidity as a main indicator of feed quality. It should be noted that the filtration process between 2 CEBs was considered as a new and independent filtration phase to be calculated. Therefore, turbidity integration will be re-calculated from 0, and corresponding to the re-calculated (Rirr/Rm)ini.

This explains why some conditions present several phases. In Figure 3 conditions. Therefore, conditions BW1/3 and BW1/4 are more suitable for long term operation at industrial scale. This result is similar to the result on seawater [START_REF] Cordier | Optimization of Air Backwash Frequency during the Ultrafiltration of Seawater[END_REF], who concluded that AB was more effective to control fouling resistance in conditions of BW1/3 and BW1/5, than that in conditions with lower AB frequency BW1/7 and BW1/9, all under the same J = 60 L•m -2 •h -1 and t = 60 min.

Hydraulic filtration performance in longterm in optimized conditions

From the above sections, the three best operating conditions on short-term experiments are J80t40BW1/3, J60t60BW1/4, and J60t60BW1/3. To verify the feasibility and sustainability of the optimized conditions, long terms tests were conducted on condition J60t60BW1/3 both in winter (from 26/2/2020 to 18/3/2020) and in summer (from 1/7/2020 to 27/7/2020). Figure 3-13 and Figure 3-14 show the permeability variation for more than 20 days, respectively, in winter and in summer. From Figure 3-13 and Figure 3-14, the UF pilot plant showed stable and continuous filtration performance, and great permeability recoveries (by CB, AB, and CEBs) during longterm operation, both in summer and winter. The occurrence of CEB were all less than once per day which meets sustainable objectives. However, the frequency of CEB is unstable, which is found to be related to the feed water quality and temperature changes. In summer, the permeability drops seem faster than in winter, but it also seems that permeability recoveries by CEB are higher than in winter. Faster permeability drops in summer can be related to more algae observed in the effluent of WWTP resulting in more suspended solids and organic matters. Therefore, the fouling potential on membrane in summer was relatively higher than in winter but at the same time the mean water temperature in summer was 27.7±1.3 ℃, while in winter it was 20.2 ± 3 ℃ which could lead to better reversibility of cleanings including AB, CB, and CEB [START_REF] Almecija | Influence of the cleaning temperature on the permeability of ceramic membranes[END_REF][START_REF] Alresheedi | Effects of feed water temperature on irreversible fouling of ceramic ultrafiltration membranes[END_REF][START_REF] Lintzos | Influence of the Backwash Cleaning Water Temperature on the Membrane Performance in a Pilot SMBR Unit[END_REF]. Indeed, the mean reversibility of AB in summer and in winter are respectively 144 ± 46% and 135 ± 21%.

Besides, the mean permeability recoveries by CEB in summer and in winter are respectively 308 ± 15% and 246 ± 30%. However, the water temperature increase had little effects on CB performance: the mean reversibility of CB in summer and winter are all around 80%. Although there was higher fouling potential on membrane in summer, the corresponding temperature increase improved cleaning efficiency of AB and CEB, finally resulting in sustainable permeability recovery and reasonable CEB frequency.

Conclusion

In this chapter, ultrafiltration is considered as tertiary treatment for municipal wastewater reuse in semi-industrial operation and for the first time some conclusions can be given:

(i) Concerning the most suitable operating conditions for UF: soft conditions with lower flux or frequent physical cleaning (short filtration time) resulted in too little productivity and were discarded. Harsh conditions with higher flux or longer filtration time were also discarded because of high occurrence of CEB which led to difficult permeability stabilization and high consumption of permeate and chemicals. Finally, standard conditions J80t40BW1/3, J60t60BW1/4, and J60t60BW1/3 stood out from the others with higher overall performances. Of course, these conditions are function of the WWTP and feed water quality, but still, this study defined some ranges of adequate operating conditions for future water managers and engineers for municipal wastewater tertiary treatment before reuse.

(ii) By analyzing the influence of AB frequency on irreversible fouling management, the irreversible fouling resistance increased faster with the decrease of AB frequency during operation.

Optimum AB frequencies of BW1/3 and BW1/4 under constant flux of 60 L⋅m -2 ⋅h -1 and t of 60 min found in (i) were confirmed.

(iii) Concerning the selected sustainable conditions, more than 20 days of operation in condition J60t60BW1/3 in winter and in summer confirmed that the UF pilot plant could provide sustainable and adaptable filtration performance regardless of the temperature and feed water quality.

Water quality analysis for reuse purpose

Permeate quality analysis is critical to the realization of water reuse. To ensure the safety and reliability of reused water in the frame of this study, the permeate quality was compared to the guidelines for water reuse. Over the course of the thesis, changes in standards, the pandemic and the emergence of pollutants (microplastics) and the possibility of developing a new analysis technique in partnership with PerkinElmer: the analysis evolved over time. European parliament regulations for water reuse [START_REF]Guidelines for the safe use of wastewater, excreta and greywater[END_REF][START_REF]relatif à l'utilisation d'eaux issues du traitement d'épuration des eaux résiduaires urbaines pour l'irrigation de cultures ou d'espaces verts -Légifrance[END_REF][13]. The removal rates between UF feed and UF permeate were calculated to evaluate the benefit of UF. Moreover, as required by the standards, the removal rates between WWTP feed and UF permeate were also calculated when possible. As a result, the UF system can greatly retain the microorganisms, including E.coli, Enterococci, spores of anaerobic sulphito-reducers, and bacteriophages, all under the detection limitation of the analysis methods. Particularly, the treatment processes in WWTP together with UF system achieved more than 5 log removal of bacteria E.coli and Enterococci. Besides, the COD, BOD5, TSS concentrations and turbidity of permeate all fulfil the three standards. However, because of the detection limit, the log removals of the spores of anaerobic sulphito-reducers and virus (Specific F-RNA bacteriophages) cannot fully reach more than 4. In fact, the concentrations of the spores of anaerobic sulphito-reducers and virus in permeate were very low and under the detection limits (< 1 CFU•100mL -1 for bacteria or < 1 PFP•100mL -1 for virus). In addition of the parameters in Table 4-1, the parameters of Salmonella, Legionella spp., and viable pathogenic helminth eggs, were tested only during Campaign 2 as mentioned in the EU regulation, and they were not found in any of the permeates. Therefore, regardless of the filtration conditions and the variation of feed water quality in this study during the first experimental campaign, UF as tertiary treatment can provide high-quality water for reuse as it reaches the WHO guidelines for reuse and the French reuse standards with quality "A". According to the results of the second experimental campaign, UF permeate also reaches the very recent EU regulation for reuse with quality "A".

Additionally, because of the international Covid-19 pandemic, coronavirus SARS-CoV-2 was measured in the raw wastewater of WWTP, UF feed, and UF permeate in November 2020.

Coronaviruses are continuously detected in different types of wastewater contaminated through several sources, such as handwashing, sputum, vomit, and feces from disease carriers [START_REF] Amoah | Coronaviruses in wastewater processes: Source, fate and potential risks[END_REF][START_REF] Lesté-Lasserre | Coronavirus found in Paris sewage points to early warning system[END_REF][START_REF] Mandal | A review on presence, survival, disinfection/removal methods of coronavirus in wastewater and progress of wastewater-based epidemiology[END_REF].

Among coronaviruses, SARS-CoV-2 responsible for the Covid-19 disease can cause possible transmission via contaminated waste surfaces and aerosols from wastewater systems [START_REF] Wölfel | Virological assessment of hospitalized patients with COVID-2019[END_REF][START_REF] Lescure | Clinical and virological data of the first cases of COVID-19 in Europe: a case series[END_REF][START_REF] Xiao | Evidence for Gastrointestinal Infection of SARS-CoV-2[END_REF].

Generally, coronavirus in wastewater can be active for several days. As reported by Bivins et al.

[277], 90% of SARS-CoV-2 in wastewater can be reduced in 1.6-2.1 days under room temperature, and 99% of SARS-CoV-2 in wastewater can be reduced in 2.9 -6.5 days under room temperature.

To ensure the safety of the water production for reuse, the detection of SARS-CoV-2 from the influent to end effluent is necessary. The results showed that the raw wastewater was tested positive with the envelope protein gene E above the detection limit (17 000 genome units per liter) but below the quantification limit (170 000 genome units per liter) and the nucleoprotein gene N was not detected. The UF feed and UF permeate were tested negative to SARS-CoV-2 by these PCR assays. Because the limit of detection of this PCR method is quite high, it is uncertain to say that the virus is completely absent in the waters or not. However, according to recent publications filters, the filtration processes were all rapid, and in apparent constant flux. The time for filtration of 1 L sample were all under 30 seconds. Therefore, the filtration apparatus supports effective filtration efficiency on clean water samples.

Looking at MPs in Table 4-2, Evian, and tap water contains less numbers and types of microplastics compared to the others while distilled water contains the most. Because the distilled water and ultrapure water are made from tap water through some advanced purification process, the increase of microplastics in distilled water and ultrapure water may come from process contamination, such as the used polymer pipes, tapes, and membranes. Looking at all particles (MPs + cellulose, salts, organics…), ultrapure water contains the lowest while tap water contains the most. In Evian water the microplastic dimensions are larger than ultrapure water and tap water. Since larger particles and/or larger amounts of natural particles such as proteins and cellulose can increase the chance of microplastics to be covered on filters, the tap water and Evian water are not recommended as rinsing waters. Through analysis, the ultrapure water can therefore be considered as the best rinsing water. To avoid the external contamination of microplastics during rinsing, the use of ultrapure water is controlled within 20 mL, with less than 1 microplastic involved averagely.

Selection of scanning pixel resolution of microscopy

The pixel size of focal array plane detector (pixel resolution) is a combination function of native focal plane array (FPA) detector element size, objective magnification and Intermediate optics magnification. On imaging of micro-FT-IR, the selection of pixel size can be 6.25 μm, 25 μm and, 50 μm. The pixel size of 50 μm is not recommended for imaging because the maximum pore size of filter in this study is 25 μm from the stainless-steel filter. To compare the differences on spectra map under different pixel size, the ultrapure water was both imaged under pixel size of 6.25 μm and 25 μm. A volume of 1 L for all the samples was filtered through a 3 μm gold coated filter with a filtration square at 6000 μm × 6000 μm.

Digestion protocols

In this study, the UF permeates are clean enough to be filtrated directly for detection without digestion process. Indeed, the quality of UF permeate is quite good, with turbidity lower than 1 NTU, total organic carbon (TOC) lower than 10 mgC•L -1 , and non-visible suspended particles.

The filtration volume of these samples on the detection filter can reach up to 500 mL to 1 L with clear visible survey by microscope. The UF feed from WWTP was filtrated in two steps to ensure all microplastics can be detected correctly. Because there are more organic matters in the UF feed than UF permeate, the UF feed sample needs to be digested. An optimisation of this digestion was realised to define the duration and the volume of reagent. Therefore, as digestion with H2O2 can reduce the influence of organic matters on MP detection [START_REF] Tagg | Identification and Quantification of Microplastics in Wastewater Using Focal Plane Array-Based Reflectance Micro-FT-IR Imaging[END_REF][START_REF] Hurley | Validation of a Method for Extracting Microplastics from Complex, Organic-Rich, Environmental Matrices[END_REF], the UF feed sample was mixed with 30% H2O2 with volume ratio at 1:1, then the samples were analysed under different digestion duration. The mixture was kept in room temperature without stirring.

Figure 4-3 shows the visible images of the filters by FT-IR microscopy. From case (a) to case (c), the samples were all filtrated through the 3μm filter with 50 mL of feed water (100 mL in total with 50 mL UF feed and 50 mL H2O2) from the same sampling bottle. It is obvious to see that the organic matters were increasingly digested with H2O2 as the reaction time extends. In view of Figure 4-3, the deposit in case (a) and case (b) is quite dense, the microplastics may be covered and failed to be detected. The samples in case (a) and case (b) were for 1 and 7 days.

After 10 days reaction, the visible images in case (c) and case (d) were much clearer than that in case (a) and case (b). However, a point worth to be noted here is the organic deposit especially in case (a) and case (b) is not mainly composed of proteins or cellulose based on the spectra maps generated by siMPle shown in Figure 4-4. Municipal wastewater treatment plants are considered as a significant source of various microplastics to enter in aquatic environment [START_REF] Liu | Transfer and fate of microplastics during the conventional activated sludge process in one wastewater treatment plant of China[END_REF][START_REF] Mason | Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent[END_REF]. To reduce microplastic pollution, the removal efficiency of microplastics by the 200 kDa UF membrane in operation in the pilot-plant was investigated in this section. Table 4-3 shows the microplastics concentration both in quantity and in total surface area for UF feed and UF permeate. In result, the UF membrane was confirmed to be effective on microplastics removal, resulting in 86.0 ± 0.6 % removal of microplastic in quantity and 97± 2 % removal in surface area. From Figure 4-5, averagely 81.5% of microplastic particles in secondary effluent were small particles with minor dimension < 40 μm and major dimension < 100 μm. Through UF membrane, the microplastic particles with minor dimension > 80 μm and major dimension > 200 μm were completely removed. From Figure 4-6, the main components of microplastics in secondary effluent include PA, PE, PP, PS, and PVC. Through comparison of microplastics removal, the removal rate in total surface area is more than that in quantity which is similar to the UF process in seawater treatment plant (not presented in this study). The result furtherly illustrates that the UF membrane filtration process may cause microplastic fragmentation similar to the above-mentioned UF filtration in seawater treatment plant. The size of the microplastics after UF is very high in comparison with the pore size (factor 1000). Actually, microplastics are everywhere and it is difficult to remove them all, as the container of the membrane and the pipes for water transportation are all made of plastics. Removal rates by UF (86.0 ± 0.6) % (97 ± 2) %

Conclusion

In summary, the UF permeate quality was detected to be good enough to be reused in nonpotable applications as it met reuse guidelines of the WHO, reuse standards of France and the most recent EU regulation for agricultural irrigation. The whole treatment process provided high removal capacity on microorganism removal. The UF permeate was resulted in more than 5 log removal rates of bacteria E.coli and Enterococci compared to the raw wastewater. Besides, the concentrations of the spores of anaerobic sulphito-reducers and virus in permeate were as low as to be under the detection limits of analytical methods (< 1 CFU•100mL -1 for bacteria or < 1 PFP•100mL -1 for virus). This works confirms the great interest of UF as tertiary treatment of conventional WWTP for water reuse. Considering the international Covid-19 pandemic right now, the UF permeate after UF treatment in this test would have no infectivity of SARS-CoV-2 and could be reused safely. Recently, microplastic contamination have attracted worldwide attention as a new emerging pollutant. The study made the optimisation on rinsing water and scanning pixel resolution selection to obtain more accurate results. The Ultrapure water as selected as rinsing water due to its lower quantity of all particles and the smaller dimensions of the tested samples compared to Evian, tap water, and distilled water. The scanning pixel size at 6.25 μm pixel resolution shows more accurate identification and quantification of particles

(a)

PA PE PP PS PVC PET abs compared to 25 μm pixel resolution. The imaging under 25 μm per pixel is good at shorter detection time and larger storage space, it is recommended to be used when the known size of microplastics is larger than 25 μm or the pore size of the filter membrane is larger 25 μm. The image on 3 μm and 5 μm filters uses the 6.25 μm pixel resolution. In results, The UF membrane could provide 86.0 ± 0.6 % removal of microplastic in quantity and 97± 2 % removal in surface area of UF feed. However, the UF system showed effective removal capacities and considerable concentration of microplastics, but the microplastics fragmentation during each treatment process seems hard to avoid. The smaller the microplastics, the greater the difficulty of removal and the greater the potential harmfulness which needs to be highly investigated in the future.

Consequently, this works confirms the great interest of UF as tertiary treatment of conventional WWTP for water reuse.

CHAPTER 5. Impacts of NaOCl-assisted backwash on UF fouling management and total economic costs

Impact of chlorinated-assisted backwash and air backwash on ultrafiltration fouling management for urban wastewater tertiary treatment

To improve membrane fouling management, the NaOCl-assisted backwash has been developed to improve permeability maintenance and reduce the need for intensive chemical cleanings.

This section is aimed to focus on the efficiency of NaOCl-assisted backwash in real UF pilot scale and with periodic classic backwash (CB) and air backwash (AB). The impacts on hydraulic filtration performance, physicochemical properties of membrane material under different addition frequency of NaOCl, and the performance of chlorinated CB and AB will be discussed. The membrane foulants fed by municipal secondary effluent includes organic fouling, inorganic fouling and microbial fouling [START_REF] Shi | Fouling and cleaning of ultrafiltration membranes: A review[END_REF][START_REF] Chen | Optimization of membrane physical and chemical cleaning by a statistically designed approach[END_REF][START_REF] Nguyen | Chemical cleaning of ultrafiltration membrane fouled by an activated sludge effluent[END_REF]. Organic fouling is the main cause of irreversible fouling for membranes. Nonetheless, the efficiency and practicality of NaOClassisted backwash has not been studied in real UF pilot scale and even less with periodic classic backwash (CB) and air backwash (AB). Therefore, this study aims to investigate the influence of NaOCl-assisted CB and/or AB on the hydraulic filtration performance and fouling management in the semi-industrial UF pilot plant with maximum flow rate of 20 m 3 •d -1

described in Chapter 2. To this aim, 4 different conditions were studied as mentioned in Table 2-7, and recalled here: Conditions NNNN, NNNY, YYYN, and YYYY for CB CB CB AB with (Y-Yes) or without (N-No) chloride. Besides, the impacts on physicochemical properties of membrane material under different addition frequency of NaOCl and the performance of chlorinated CB and AB will also be discussed.

Permeability variation

During filtration, the permeability variation gives the hydraulic filtration performance of the UF membrane, as shown in Figure 5-1. According to Figure 5-1, the turbidity of UF feed was stabilized around 1 NTU in all conditions. Yet the turbidity shows slight periodical variation with time in a day because the feed water quality seems positive correlated to the variations of raw wastewater flow rate as demonstrated in Chapter 3. Besides, the temperature of 4 conditions is 21 ± 2 ℃ and there is also a cyclical variation of temperature during the day and night.

Nevertheless, the variation of feed water quality was undergone of all conditions, thus the feed water quality can be considered to have the similar effect on the 4 conditions. From CEB occurrences, condition NNNN was resulted in the highest frequency of CEB, with 1 CEB per day. Additionally, condition YYYY had 1 CEB in 5 days, condition NNNY had in 1 CEB in 5 days, and condition YYYN has 1 CEB in 6 days operation but these 3 last conditions are similar.

From permeability stability, condition NNNN showed the fastest decrease of permeability to 200

L•m -2 •h -1
•bar -1 which triggered CEB cleaning. Condition NNNY showed stable variation of permeability, the addition of NaOCl only in AB largely improved the UF filtration performance compared to NNNN, with only 1 CEB occurrence in 5 days. In this condition, the CEB occurred at the 1 st day of operation and there is no more CEB in the last 5 days. The reason for faster permeability decreases at 1 st day may be due to the variation of feed water quality, or the newly cleaned membrane was sensitive to cake deposition which was in higher chances of pore blocking and lower reversibility of backwash. Similarly, Ye et al. [START_REF] Ye | Effects of operating conditions on submerged hollow fibre membrane systems used as pre-treatment for seawater reverse osmosis[END_REF] found less reversible fouling in the first few cycles filtration of seawater than in the following cycles. In whole filtration, the permeability in condition NNNY showed a gradual downward trend. The permeability after stabilization in condition YYYN showed the most sustainable variation during one-week filtration, stabilized at 260-580 L•m -2 •h -1 •bar -1 , while the permeability in condition NNNN, NNNY, and YYYY were stabilized on average at around 200-500

L•m -2 •h -1 •bar -1 , 230- 580 L•m -2 •h -1 •bar -1 , and 300-650 L•m -2 •h -1 •bar -1
, respectively (some individual highs and lows and initial permeability are not taken into account). It seemed that the efficiency of physical backwashes in YYYN was just balanced to the accumulation of fouling rates especially after 2day operation and the permeability after backwash could achieve to 100% recovery. So far, the addition of NaOCl in either AB or CB could improve the membrane filtration performances greatly, including more sustainable permeability variation and less CEB occurrences.

The recovered permeability in condition YYYY after backwashes was higher than the others which can achieved to 700 L•m -2 •h -1 •bar -in the first two days. The CEB in condition YYYY was triggered on the 2 nd day of filtration, the fast decrease of permeability was mainly occurred in the 5-6 filtration cycles before CEB. Except the rapid permeability decrease on the 2 nd day, the peak of permeability and average permeability were both higher than the other conditions.

Considering that the variation of turbidity in that period was in regular ranges, the exceptional rapid decrease of permeability may be caused by other parameters that are not taken in account, such as the organic matters in the feed water. A difference of YYYY condition with the other 3 conditions was the peak permeability values. The UF membrane was strongly cleaned by CEB before each condition started which indicated that both the reversible and irreversible fouling can be removed greatly. The fouling formation in the first few cycles of each condition may be mainly because of pore blocking which is irreversible, thus the permeability decreased faster at the beginning of filtration than in the following cycles [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF][START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF], the physical backwash normally cannot recover the permeability back to the initial levels because of their poor separation strength on irreversible foulant. From Figure 5-1, it can be seen obviously the fast decrease of permeability at the first few cycles in conditions NNNN, NNNY, and YYYN, and even after automatic CEB, the permeability hardly reached 650

L•m -2 •h -1 •bar -1 .
In condition YYYY, the permeability could be easily recovered to the 700 L•m - 2 •h -1 •bar -1 with all NaOCl-assisted physical backwashes. Before condition YYYY, the pilot plant was just finished with the condition YYYN that already maintained the membrane in very good permeability variation. With NaOCl addition both in CB and AB, it seems that the condition YYYY can reach to more than 100% recovery of the decreased permeability in a filtration cycle.

The increase of permeability was also observed by Alhweij et al. and Wienk et al. [START_REF] Wienk | Chemical treatment of membranes of a polymer blend: Mechanism of the reaction of hypochlorite with poly(vinyl pyrrolidone)[END_REF][START_REF] Alhweij | Self-doped sulfonated polyaniline ultrafiltration membranes with enhanced chlorine resistance and antifouling properties[END_REF]. The UF membrane showed quite good removal efficiency on parameters such as turbidity, microplastics, bacteria, virus and organic matters of UF feed in all conditions, the permeate quality was detected to be good enough to be reused in non-potable applications as it met reuse guidelines of the WHO, reuse standards of France and the most recent EU regulation for agricultural irrigation as shown in Chapter 4.

To summarize the disinfection efficiency of NaOCl, values for concentration multiplied by contact time (CT) considering backwash and CEB occurrences based on the above performance of each condition, were estimated for a simulated 10 years of operation (Table 5-1). The frequency of CEB occurrence of NNNN, NNNY, YYYN, and YYYY here are estimated after feedback of this study as once per day, once in 5 days, once in 6 days, once in 5 days. Referring on impacts of chlorinated disinfectants on membranes, many studies have reported that NaOCl can attack the chemical bonds of polymeric membranes and degrade the membrane material due to long term exposure or excessive dosage of chemicals [START_REF] Luo | Distinct effects of hypochlorite types on the reduction of antibiotic resistance genes during waste activated sludge fermentation: Insights of bacterial community, cellular activity, and genetic expression[END_REF][START_REF] Hanafi | Electrokinetic analysis of PES/PVP membranes aged by sodium hypochlorite solutions at different pH[END_REF][START_REF] Alhweij | Self-doped sulfonated polyaniline ultrafiltration membranes with enhanced chlorine resistance and antifouling properties[END_REF][START_REF] Gohil | Chlorine attack on reverse osmosis membranes: Mechanisms and mitigation strategies[END_REF][START_REF] Son | Preparation and characterization of polyamide reverse-osmosis membranes with good chlorine tolerance[END_REF].

Similarly, excessive chlorine can impact the PES membranes, but the degree of impact varies a lot in different studies. Some studies pointed out the occurrence of a PES-chain scission and PES material degradation though excessive chlorination, such as after 28500 mg•L -1 total free chlorine of NaOCl (27160 mg Cl2•L -1 ) contact for 8 months [START_REF] Kourde-Hanafi | Influence of PVP content on degradation of PES/PVP membranes: Insights from characterization of membranes with controlled composition[END_REF], or after 200-2400 mg•L -1 total free chlorine of NaOCl mg Cl2•L -1 )contact for 10-60d [START_REF] Hanafi | Electrokinetic analysis of PES/PVP membranes aged by sodium hypochlorite solutions at different pH[END_REF]. Fu and Zhang carried out the proposed PES degradation mechanisms that the PES may undergo a chain scission of the backbone structure into sulfonic acid groups and phenyl chloride groups [START_REF] Fu | Chemical aging and impacts on hydrophilic and hydrophobic polyether sulfone (PES) membrane filtration performances[END_REF]. Hanafi et al. [START_REF] Hanafi | Electrokinetic analysis of PES/PVP membranes aged by sodium hypochlorite solutions at different pH[END_REF] showed that exposure of PES/PVP membranes to NaOCl even led to the appearance of macrovoids in the membrane sub-layer. In contrary, some researchers found slight modification on PES membranes. Alhweij et al. [START_REF] Alhweij | Self-doped sulfonated polyaniline ultrafiltration membranes with enhanced chlorine resistance and antifouling properties[END_REF] found that only slight changes in PES surface roughness was observed after exposure to 238 mg Cl2•L -1 NaOCl for 3 days. The permeability of PES membrane increased by 74% after chlorine exposure, but SEM images confirmed that there were no observed structural damages on the membrane. Wypysek et al. [START_REF] Wypysek | Shell and lumen side flow and pressure communication during permeation and filtration in a multibore polymer membrane module[END_REF] also stated that a damaged separation skin does not have a significant negative influence on filtration performance of PES membrane. Yadav et al. [START_REF] Yadav | Effects of hypochlorite treatment on the surface morphology and mechanical properties of polyethersulfone ultrafiltration membranes[END_REF] also mentioned that the changes of PES membrane surface properties was observed after exposure to 10000-25000 mg•L -1 •day of NaOCl (9530-23825 mg Cl2•L -1 •day) at pH 9-12, but no great changes were observed on membrane mechanical properties and tensile strength. However, according to Wang et al. [START_REF] Wang | Lab-scale and pilot-scale fabrication of amine-functional reverse osmosis membrane with improved chlorine resistance and antimicrobial property[END_REF], long time exposure to chlorine could impact physical and chemical properties of membranes regardless of the chlorine concentration. This phenomenon can be explained by the study of Abdullah and Bérubé [START_REF] Abdullah | Assessing the effects of sodium hypochlorite exposure on the characteristics of PVDF based membranes[END_REF] who stated that the more accurate relationship of chemical exposure to membranes should be C n T, not the CT. "n" is the power coefficient and was determined <1 from their experiment, which indicated that the contact time of cleaning had a more severe impact on the changes in the physical/chemical characteristics of the membranes than the NaOCl concentration. From Table 5-1, condition NNNY represented the lowest CT of NaOCl and equivalent consumption per m 3 of permeate compared to the others while condition NNNN represented the highest. Although the CT with NaOCl in condition YYYY was less than NNNN, they provided higher contact frequency of NaOCl contact to membranes. Therefore, it is not recommended to apply YYYY and NNNN condition for long-term filtration purposes in case of the irreversible changes on the membrane.

Fouling resistance

This part investigates the influence of chlorinated backwash on fouling composition. Figure 5-2 shows the variation of fouling resistance at the end of each filtration cycle in the four conditions, membrane resistance (Rm) was considered related to the initial permeability in each condition (650 L•m -2 •h -1 •bar -1 ) thus was constant at 5.51×10 11 m -1 in all conditions. From Figure 5-2, the Rirr and Rre in condition NNNN increased rapidly between neighbouring CEBs which can easily increase over Rm. This situation can refer to Akhondi et al. [START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF] who confirmed the increase of fouling rate with periodic physical backwash under constant flux and dead-end filtration mode, and the fouling rate could be highly increased when the fouling achieves to a certain amount, together with poor reversibility and cleaning efficiency. In contrary, the variation of Rirr and Rre in conditions with NaOCl in backwashes (NNNY, YYYN, YYYY) were mostly under the Rm. Actually, it is important to limit the fouling deposition on membrane, especially the Rirr on membrane due to its negative impacts on hydraulic filtration performance and cleaning efficiency. In condition NNNY, the addition of NaOCl in AB largely decreased Rirr and Rre compared to NNNN. Ignoring the filtration from the beginning to the 1 st CEB, the overall Rirr variation can be separated into two parts, the slower increasing rate of overall Rirr from the 2 nd to 5 th day and the faster increasing rate of overall Rirr from the 5 th to 7 th day shown by the red dashed lines in Figure 5-2. In filtration from 2 nd to 5 th day, the overall Rirr increasing rate was in slow and steady growth during constant flux dead-end filtration. From each backwash sequence (4 filtration cycles with CB, CB, CB, AB), the Rirr accumulated on membrane increased in the first 3 filtration cycles with CBs and significantly decreased after an AB with NaOCl which controlled the overall Rirr at lower increasing rate. CB without NaOCl could carry away partial cake foulant from membrane surface, but could not remove the smallest compounds adsorbed onto the membrane material effectively, when filtration restarts the residual foulant will adhere to the membrane surface again and accumulated continuously [START_REF] Ye | Evolution of fouling deposition and removal on hollow fibre membrane during filtration with periodical backwash[END_REF]. AB itself has powerful strength with air injection to loosen the foulant layer and to break and/or carry away the smaller particles blocked and absorbed into membrane [START_REF] Cordier | Air Backwash Efficiency on Organic Fouling of UF Membranes Applied to Shellfish Hatchery Effluents[END_REF]. Then after air injection, backwash with NaOCl can inactivate the microorganisms and oxidize organic matters deposited on membrane.

The cooperation of air flow and NaOCl greatly improved the backwash efficiency on foulant cake removal. When the fouling resistance achieved to a certain value, the AB and CB cleaning efficiency was decreased and the accumulation of integral foulant on membrane became faster than before. Thus, in filtration from 5 th to 7 th day, a higher overall Rirr rate was observed and the fouling cake seemed hardly to be removed by CBs and unable to be controlled by ABs. This suggests that as the continuous accumulation of fouling deposition, the foulant cake maybe changed to a more compact structure. The increased fouling rate may be caused by increased local flux due to loss of effective filtration area by irreversible fouling. The strength of physical backwash was powerless in front of the increased fouling layer, and maybe the exposure of NaOCl to fouling layer became useless due to the low concentration and short contact time.

The distribution of Rirr and Rre in condition YYYN were in the most stable variation, and Rirr was lower than Rre and lower than Rm (Rirr < Rre < Rm) .i.e. so it appears that adding chlorine to The fouling rate was measured to be very low and the fouling layer deposited in a filtration cycle seemed to be fully removed by backwashes. There is no more accumulation of Rirr after CBs in a backwash sequence in contrast to condition NNNY, thus the fouling removal efficiency of CB was largely improved by NaOCl addition. Normally, the PES/PVP blended membranes shows superior hydrophilicity, anti-fouling, oxidative and thermal stability as well as good mechanical property [START_REF] Vatsha | Preparation of antifouling polyvinylpyrrolidone (PVP 40K) modified polyethersulfone (PES) ultrafiltration (UF) membrane for water purification[END_REF][START_REF] Zhao | Modification of polyethersulfone membranes -A review of methods[END_REF]. But when looking at the condition YYYY, although the value of Rirr and Rre were both under Rm, the variation of Rirr was in high volatility compared to YYYN. The Rirr sometimes increased very fast, sometimes it was even lower than that in YYYN. Otherwise, the total fouling resistances (Rirr + Rre) in conditions NNNY, YYYN, and YYYY were in similar ranges, around 4-7×10 11 m -1 except the points around CEB in condition NNNY and YYYN. As the CEB is triggered at TMP ≥ 0.3 bar for 60s, the corresponding total fouling resistances is at 1.41×10 12 m -1 at 20 ℃. The total fouling resistances in conditions NNNN was higher, which resulted in frequent occurrence of CEB.

Fouling reversibility by physical backwashes

From the previous analysis, the addition of NaOCl in CB and AB improves the backwash cleaning efficiency, but it is not clear to know how far it can be improved. Therefore, it is necessary to compare the fouling reversibility (Eq.( 8)) in different backwash conditions.

According to the membrane filtration model by Kalboussi et al. [START_REF] Kalboussi | Optimal control of physical backwash strategy -towards the enhancement of membrane filtration process performance[END_REF], the mass of the cake layer tends towards a constant value as the number of filtration cycles increase. According to the TMP variation in dead-end filtration with periodic backwashes [START_REF] Akhondi | Evaluation of fouling deposition, fouling reversibility and energy consumption of submerged hollow fiber membrane systems with periodic backwash[END_REF][START_REF] Remize | Evaluation of backwash efficiency, definition of remaining fouling and characterisation of its contribution in irreversible fouling: Case of drinking water production by air-assisted ultra-filtration[END_REF], the fouling resistance at the end of each filtration cycle would be in increasing trend with filtration cycles continues, therefore the fouling condition before AB is much closer to that before the 3 rd CB. Therefore, the fouling distribution before AB is much closer to that before the 3 rd CB. was controlled in the lowest ranges in YYYN compared to the others with chlorinated CB and indicated that the membrane was rather clean, therefore, the total foulant cake before AB in YYYN would be less than that in conditions NNNN and NNNY which dealt with both the cake layer formed in one filtration cycle and accumulated foulant after the previous three CBs.

Therefore, the cleaning performance by AB in YYYN did not exert its best removal ability compared to that in NNNY condition. On the other hand, although backwash condition YYYN largely improved the fouling management, there was still residual Rirr left on membrane after chlorinated CB, but non-chlorinated AB failed to remove these residual foulant which reflected its limitation in particular on Rirr removal, while chlorinated AB in condition YYYY could achieve much lower value of Rirr if the sensitivity of the membrane to fouling is ignored. The cases of CB in Figure 5-5 includes the 1 st CB, 2 nd CB, and 3 rd CB of all backwash sequences.

The statistical test showed positive linear regression between AB reversibility and Rirr before AB in all conditions (p-value<0.05), and showed significant negative linear regression on CB reversibility and Rirr before CB in condition NNNN, YYYN, and YYYY; only the statistical test for condition NNNY (0,05 < p=0.066) is not significant. However, the data here were mainly shown to know the variation tendency (increase or decrease not necessarily linearly) of the AB or CB reversibility versus total irreversible fouling resistance before the backwash. Therefore, the significances of both AB and CB under 90% confidential interval can be totally supported.

The reversibility of AB whether with or without NaOCl was shown in positive correlation to Rirr from Figure 5-4, while the reversibility of CB with or without NaOCl was shown in negative correlation to Rirr from Figure 5-5. It means that the cleaning capacity of AB will be increased with the increase of Rirr leading to better filtration performance, but the removal capacity of CB will be decreased with the increase of Rirr causing harsh filtration performance. From Figure 5-4, the increasing rates of AB reversibility with Rirr in all conditions were similar, the reversibility of AB under the same Rirr was order in YYYY higher than NNNY, higher than NNNN and YYYN. The addition of NaOCl in AB indeed improved its cleaning efficiency as NNNY and YYYY were both in higher reversibility compared to NNNN and NNNY whatever the value of Rirr.

From Figure 5-5, the reversibility of CB was decreased with the deposited Rirr increase and validated the higher performance of AB in comparison to CB.

Turbidity and TOC removal rates by backwash

In general, as the cake layer mass grows in proportion to the concentration of foulants in the feed, and to the total volume of feed passing through the membrane, the cake layer resistance is proportional to the mass accumulated on the membrane surface [START_REF] Kalboussi | Optimal control of physical backwash strategy -towards the enhancement of membrane filtration process performance[END_REF]. Table 5- compared to non-chlorinated 3 rd CB. Additionally, the turbidity removal performance of AB was much better than CB, as the lowest removal rate is around 88% averagely. The chlorinated AB in condition NNNY showed the highest, 136% removal of turbidity from concentrate which means the chlorinated AB removed the total turbidity accumulated in its own filtration cycle completely and removed part of the residual turbidity from the previous filtration cycles. The turbidity recovery performances of AB in conditions NNNN, YYYN, and YYYY were very similar, the chlorinated AB in condition YYYY showed no improvement on turbidity removal.

The removal efficiency of AB in condition NNNY was the highest compared to the other 3 conditions almost in similar efficiency.

From Figure 5-6 (b), it is obvious to see the high improvement of TOC recovery in conditions with NaOCl compared to NNNN. In condition NNNN, the 3 rd CB and AB both without NaOCl showed similar and low removal efficiency on TOC. TOC recovery rate by chlorinated AB was highly improved to more than 200% while by 3 rd CB, it was only 50% in condition NNNY.

Otherwise, the addition of NaOCl in CB also greatly improved the TOC recovery rates as in conditions YYYN and YYYY. Through comparison, the addition of NaOCl in CB showed higher removal capacity on TOC compared to turbidity removal. Through comparison, the condition NNNN was not suggested for operation because of the frequent CEB occurrence, fastest Rirr increase and poor cleaning efficiency by CB and AB.

Condition YYYY was not recommended because of its potential damage on membrane material with most frequent contact with NaOCl, unstable permeability and Rirr variation, and unstable cleaning efficiency of CB. YYYN was resulted in the best fouling resistance control and permeability recovery, but the chlorinated CB showed lower reversibility when faced with higher Rirr on the membrane. Additionally, the addition of NaOCl in condition YYYN will be higher that NNNY under the same operation period, which would increase the operating costs and may cause faster damage on membrane structures in the long term. Although the control of Rirr in condition NNNY was not as good as in condition YYYN, it was in slight and sustainable increase resulted in only 1 CEB occurrence in 6 days. The comparison of total costs depending on the 4 conditions will be discussed at the end of this chapter but condition NNNY seem to be the most

The influence of NaOCl concentration on air backwash efficiency of condition NNNY

As backwash sequence has been optimized in condition NNNY, it is necessary to furtherly investigate the performance of NNNY condition with different concentration of NaOCl addition.

The concentration of NaOCl at 5 mg Cl2•L -1 and 10 mg Cl2•L -1 in condition NNNY are compared on the filtration performance. The long-term filtration results of 5 mg Cl2•L -1 NaOCl condition has already been shown in Chapter 3, of which the frequency of CEB occurrence was once in 3 days. In this study, the CEB occurred once in 6 days in NNNY with 10 mg Cl2•L -1 NaOCl. To be compared, the variation of Rirr at the end of each filtration cycle in 5 mg Cl2•L -1 NaOCl and 10 mg Cl2•L -1 NaOCl conditions was shown in Figure 567. The Y axis Rirr-end (n) /Rirr-end [START_REF] Mudgal | European Commission, Directorate-General for the Environment[END_REF] represents the increasing ration of Rirr-end during filtration, and X axis represents the foulant cake mass accumulation during filtration. Within 1000 NTU•min integration, the variation of Rirr-end (n) / Rirr-end (1) in condition with 5 mg Cl2•L -1 and 10 mg Cl2•L -1 of NaOCl was closer to each other, and the ration of Rirr-end (n) / Rirr-end (1) was all under 5. After this, the Rirr increasing rate in 5 mg Cl2•L -1 NaOCl condition was increased very fast than before 1000 NTU•min integration, while the variation in 10 mg Cl2•L -1 NaOCl condition was continuously in sustainable and slight increase. The Rirr variation in condition NNNY with 5 mg Cl2•L -1 and 10 mg Cl2•L -1 NaOCl was indeed from 1.02×10 11 m -1 to 9.17×10 11 m -1 , and from 1.35×10 11 m -1 to 6.57×10 11 m -1 , respectively. The faster increase of Rirr-end after 1000 NTU•min integration in 5 mg Cl2•L -1 NaOCl condition may be due to more complex structure of foulant cake layer and increased local flux due to loss of effective filtration area, as stated in section 5.1.2 of condition NNNY. Higher concentration of NaOCl at 10 mg Cl2•L -1 increased the chance to inactivate organisms, detach cake foulant, extend the time to form more complex fouling, and improve the load capacity on feed water quality. Therefore, the increase of NaOCl concentration in condition NNNY indeed improved the AB cleaning efficiency and the overall Rirr control during filtration. 10 mg Cl2•L -1 NaOCl is more effective on fouling control in condition NNNY.

Discussion

In this study, 10 mg Cl2•L -1 NaOCl addition in backwash water can positively improve the filtration performance of UF pilot plant. The addition of NaOCl had significant improvement on AB cleaning efficiency when comparing condition NNNN and NNNY, or comparing condition YYYN and YYYY, resulting in 15-18% increasing of reversibility. However, NaOCl addition itself almost had fewer improvement on 3rd CB cleaning, with averagely 1-5% increasing of reversibility when comparing condition NNNN and YYYN, or condition NNNY and YYYY. In this case, it seems that air injection contributes to enhance the NaOCl-assisted backwash cleaning. In the process of this study, air injection with strong forces to break the foulant layer on membrane to be less dense thus increase the foulant contact area with backwash water and NaOCl. The cooperation of air injection and NaOCl oxidation on fouling highly improved the cleaning efficiency of backwash. Additionally, comparing the performance of AB and 3 rd CB in all conditions, the reversibility of AB (with or without NaOCl) was completely higher than that of CB (with or without NaOCl). Therefore, it seems that the effects of air injection on CB were more significant than NaOCl assistance in CB water, this can be considered as AB without NaOCl in this study has higher cleaning efficiency than CB with NaOCl, see as in condition YYYN. Based on the comparison on efficiency of chemical cleaning and physical cleaning from Park et al. [START_REF] Park | Application of Physical and Chemical Enhanced Backwashing to Reduce Membrane Fouling in the Water Treatment Process Using Ceramic Membranes[END_REF], extending contact time of chemical cleaning was one of the important factors on improvement of membrane permeability recovery compared to physical cleaning. In our study, the contact time of chlorinated backwash water through membrane is 52s in total. The disinfection and oxidation reactions between NaOCl and cake foulants cannot be completely reacted in shorter contact time, thus the cleaning efficiency of chlorinated CB was limited in this study. In contrast, the physical assistance by air injection could greatly improve the cleaning efficiency. As from Guigui et al. [START_REF] Guigui | Air sparging backwash in ultrafiltration hollow fibres for drinking water production[END_REF], air injection even at very low air velocity (0.08 m•s -1 ) could result in a high backwash efficiency. And normally, the duration of air injection does not need too long, less than 2 min is enough. Based on above analysis, air injection assistance on CB (AB) indeed provides higher contributions on fouling removal than 10 mg Cl2•L -1 NaOCl.

However, the comparison conditions of AB and NaOCl assisted CB in this study could be completed with consideration of all impact factors. The impact factors include air injection duration, air velocity, NaOCl concentration in backwash water, temperature, and NaOCl contact time with membrane. Additionally, the co-effects among these factors are complex and could be investigated in the future.

Conclusion

It is the first time that a comparison between air injection and/or NaOCl addition was realised in semi-industrial conditions. In conclusion, 10 mg Cl2•L -1 NaOCl addition in backwash water is confirmed to greatly improve the overall filtration performance and backwash cleaning efficiency based on the analysis on filtration permeability, fouling resistance distribution, backwash reversibility, and cake layer removal ability. During experiment, the chronological order of conditions is NNNN, NNNY, YYYN, and finally YYYY. The type of backwash among all conditions is 3 CBs followed with 1 AB. N represents a backwash either CB or AB without NaOCl and Y represents a backwash either CB or AB with NaOCl. First, condition NNNY stands out from the others due to better control of Rirr, less NaOCl consumption in 10 years prediction, sustainable and adaptable filtration performance, and less potential damage on the physicochemical properties of membrane. The secondary best condition is YYYN which resulting in the best fouling control and permeability recovery, but it has higher potential to damage membrane structures under frequent NaOCl addition. Second, in all conditions, AB showed positive correlation of reversibility and Rirr increase, but CB showed negative correlation of reversibility and Rirr increase. Besides, CB even added with 10 mg Cl2•L -1 NaOCl hardly exceeded the reversibility of AB without chlorine. These results reflect that AB itself whether with or without NaOCl has high cleaning efficiency on fouling removal, especially better on Rirr control. Through comparison of 5 mg Cl2•L -1 and 10 mg Cl2•L -1 NaOCl in condition NNNY, higher NaOCl concentration increased the chance to inactivate organisms, detach cake foulant, extend the time to more complex fouling formation, and improve the load capacity on feed water quality. Therefore, condition NNNY with 10 mg Cl2•L -1 NaOCl was mostly recommended for long term operation in this study on secondary effluent treatment. To further assess the applicability of the process, the total costs of semi-industrial scale UF for water reuse under different operating conditions will be assessed in the next section.

Capital expenditure and operational

expenditure of semi-industrial scale UF for water reuse

Economic cost in operating condition J60t60BW1/3

Based on results of chapter 3, the condition J60t60BW1/3 with 10 mg Cl2•L -1 NaOCl addition in AB water is recommended for the future treatment of secondary effluent of WWTP.

Before production and application in reality, it is necessary to estimate the economic budget of the project. The calculations with 10 mg Cl2•L -1 NaOCl addition as recommended in the previous section will be given in section 5.2.3. The daily volume of wastewater to the WWTP is 3200m

Impact of different NaOCl addition on economic cost

In J60t60BW1/3, based on the performance of NaOCl addition conditions NNNN, NNNY, YYYN, and YYYY, the main difference on economic cost is the chemical cost due to the frequency of CEB occurrence and NaOCl addition frequency in physical backwashes changes.

Besides, the concentration of NaOCl was 10 mg Cl2•L -1 added in the backwash water in these conditions. Table 5-11 recalls the cost of each condition through applying the changes into the formula from Table 5-4 to Table 5-10 in section 5.2.1. Figure 5-8 shows the components of CAPEX and OPEX. The CAPEX of all the conditions is the same as they use the same pilot plant and UF membrane module. The OPEX of condition NNNN will spend the most because the frequent CEB will consume more chemical cost although there is no addition of NaOCl in backwashes. Condition NNNY resulted in the most economical OPEX and the lowest cost of unit product compared to the others. The OPEX of condition NNNY is 2917.3 €•yr -1 and the unit price of permeate is 1.28 €•m -3 . This unit price of permeate is very important in comparison with the production cost of drinking water by UF which is around 0.5 €•m -3 . The difference is due to the smaller size of the plant in this study, the cost of the plant (include the module) represents more than 58% of the unit price. Moreover, due to the quality of the feed water (from WWTP), the cost of chemical is also important to represent around 23%. In the same condition J60t60BW1/3 and NNNY, the OPEX and unit cost of product of condition with 10 mg Cl2•L -1 NaOCl addition in backwash water is finally lower than that with 5 mg Cl2•L -1 NaOCl addition.

In view of economic cost, condition J60t60BW1/3 with 10 mg Cl2•L -1 NaOCl addition in AB (NNNY) is recommended for the most cost-effective and optimized condition in long-term operation. Selection of UF membrane. The filtration performances of three UF membranes were compared in lab-scale. The 200 kDa hollow fiber membrane stands out from the others with a high initial permeability at 960 L•h -1 •m -2 •bar -1 , the lowest fouling increasing rate during filtration, and larger membrane specific areas due to the geometry. Thus, the 200 kDa hollow fiber is considered to be the most adequate membrane for semi-industrial pilot scale and more especially after the settling tank (clarifier) directly without pretreatment.

Qualified water quality for reuse. The WWTP with UF treatment process provided significant removal capacity on turbidity, organic matters, microorganisms, and microplastics.

The UF system provided higher than 5 log removal rates of E.coli and Enterococci compared to the raw wastewater, and the spores of anaerobic sulphito-reducers and virus in permeate were removed to be under the detection limits of analytical methods (< 1 CFU•100mL -1 for bacteria or < 1 PFP•100mL -1 for virus). Considering the international Covid-19 pandemic, the UF permeate was free from infectious SARS-CoV-2. Concerning microplastic particles, the UF membrane provided 86.0 ± 0.6 % removal of microplastics in quantity and 97± 2 % removal in filter surface area from UF feed. However, although the UF system showed effective removal capacities of microplastics, the microplastics' fragmentation during each treatment process seems hard to avoid and needs to be furtherly investigated. Finally, the UF permeate quality was confirmed to be good enough to be reused in non-potable applications as it met reuse guidelines of the WHO, reuse standards of France and the most recent EU regulation for agricultural irrigation, all with the highest quality level "A". This works confirms the great interest of UF as tertiary treatment of conventional WWTP for water reuse for different non potable application. CEBs and water recovery rates. The optimized conditions resulted in higher than 90% water recovery rates, the fouling reversibility by AB and CB were in ranges of 135%-145% and 78%-84%, respectively. The fouling resistances were better controlled in slower increase compared to the other conditions resulting in less CEB. Of course, these conditions are function of the WWTP and feed water quality, but for the first time, this study defined some ranges of operating conditions for future water managers and engineers for municipal wastewater tertiary treatment before reuse. Sustainable and long-term filtration investigation. After optimization of the filtration conditions, the condition J60t60BW1/3 was operated for more than 20 days both in winter and in summer. The occurrences of CEB were all less than once per day which meets sustainable objectives. In summer, feed water quality became worse compared to that in winter with more bacteria, algae, and insects contributing to higher fouling potential, meanwhile, the higher temperature in summer improved the cleaning effects of CEB, CB, and AB which in turn maintained the filtration performance in sustainable permeability recovery and reasonable CEB frequency. The results confirmed that the UF pilot plant could provide sustainable and adaptable filtration performance regardless of the temperature whatever the feed water quality. These results reflect that AB itself whether with or without NaOCl has excellent cleaning efficiency on fouling removal, especially to control the increase of Rirr. Through comparison of 5 ppm and 10 ppm NaOCl in condition NNNY, higher NaOCl concentration increased the chance to inactivate organisms, detach cake foulant, extend the time to more complex fouling formation, and improve the load capacity on feed water quality. Therefore, condition NNNY with 10 ppm NaOCl was mostly recommended for future operation.

Effects of flux and filtration time on UF

Effects of

Impact of

Estimation of CAPEX and OPEX on UF pilot plant.

To furtherly assess the applicability of the process, the total costs of semi-industrial scale UF for water reuse were estimated. OPEX is the day-to-day cost, including the cost of replacing consumables (e.g., ultrafiltration membranes), chemicals and energy, maintenance, and labour. CAPEX is determined as the depreciation of the fixed assets, including the cost of the investment and the UF modules. In result, the pilot plant in condition J60t60BW1/3 with 5 ppm NaOCl addition in air backwash was resulted in CAPEX of 2940 ۥyr -1 and OPEX of 3324 ۥyr -1 . The net price of unit production is 1.39 ۥm -3 to implement UF as tertiary treatment in semi-industrial scale for water reuse. In backwash conditions NNNN, NNNY, YYYN, and YYYY, the OPEX of condition NNNY is the lowest which is 2917.3 ۥyr -1 and the unit price of permeate is 1.28 ۥm -3 . In condition J60t60BW1/3 under NNNY, the OPEX and unit cost of product of condition with 10 ppm NaOCl addition in backwash water is finally lower than that with 5 ppm NaOCl addition. In view of economic cost, condition J60t60BW1/3 with 10 ppm NaOCl addition in AB (NNNY) is recommended for future operations. However, among all conditions, the unit price of permeate is very important in comparison with the production cost of drinking water by UF which is lower than 0.5 ۥm -3 but in agreement with the state of the art. The difference is due to the smaller size of the plant in this study, the cost of the plant (including the module) represents more than 58% of the total price.

Moreover, due to the quality of the feed water (from WWTP), the cost of chemicals is also high and represents around 23%. It is clear that this cost would be much lower at industrial scale thanks to economy of scale.

Perspectives. From the end of the 20 th century, the benefits of promoting water reuse from wastewater to supplement water resources have been recognized by most countries and regions.

Although many treatment processes have been reported to achieve wastewater reuse standard or guidelines, the water reuse projects presently implemented are still very few compared to the large quantity of wastewater discharged all over the world. The total volume of water reuse is approximately 14.2 billion m 3 •y -1 worldwide reported in Global Water Market 2017, which is less than 4% of the total volume of domestic wastewater. However, the ultimate decision to promote wastewater reuse depends on economic support, government regulations and policies, public acceptance, security and requirements for reliable water supply in local conditions. The wastewater reuse guidelines are not unified in the world even for the same water reuse purpose.

Therefore, continuous improvement in the existing reuse standards and guidelines by revising/expanding is necessary. Control and monitoring during reuse applications along with the public feedback is also necessary for safety assessment. It is also worth noting that cultural and religious differences guide public opinion and acceptance of wastewater reuse. In addition, some developing countries still implement the direct use of treated wastewater without accordance with standards and associated risks. In this case, it is suggested to enact wastewater quality standards step-by-step, over suitable periods and according to treatment capabilities, for different countries and regions.

Membrane fouling and its consequences in terms of operating costs and plant maintenance remains the critical limiting factors affecting the widespread application of UF for wastewater treatment. Backwash is the commonly used and effective methods for membrane fouling control.

Compared to CEB, the conduction of backwash is fast, short, periodic, and leads to low damage to membranes. Although intensive efforts have been dedicated to the study on membrane fouling mechanisms and control, it is still necessary to develop more effective and easier cleaning methods to control and minimize membrane fouling especially in full-scale applications. The assisted process for backwash such as air injection or chemical assistance are both confirmed effective for improvement of backwash efficiency. However, the comparison on effectiveness of air backwash and chemical-assisted backwash and the influencing factors between them has not been studied yet. Normally, air injection even at very low air velocity (0.08 m/s) could result in a high backwash efficiency within shorter contact time [START_REF] Guigui | Air sparging backwash in ultrafiltration hollow fibres for drinking water production[END_REF]. Although chemical-assisted backwash, such as NaOCl -assisted backwash provides higher removal efficiency compared to backwash, extending contact time is an important factor for cleaning improvement compared to physical cleaning according to from Park et al [START_REF] Park | Variation and prediction of membrane fouling index under various feed water characteristics[END_REF]. It would be interesting to investigate the degree of cleaning efficiency improvement by impact factors such as air injection duration, air velocity, NaOCl concentration in backwash water, temperature, and NaOCl contact time with membrane. The co-effects among these factors are complex and the effects of physical assistance or chemical assistance on backwash efficiency and their influencing factors could be seriously investigated in the future.

This dissertation emphasized the performances of the UF system on contaminants removal capacity, microorganisms and microplastics removal capacity, membrane fouling potential, cleaning efficiency, water recovery rate and economic cost. The UF pilot plant was confirmed to successfully meet the water reuse standards both from France and from the European parliament. Furthermore, future research focusing on micropollutants removal, fouling mechanism strategies, and life cycle assessment of membrane-based municipal wastewater treatments, for potable and non-potable reuse applications, continues to need further systematic investigation.

List of Figures

Ultrafiltration as urban wastewater tertiary treatment for water reuse at semiindustrial scale -Abstract

Water reuse is a sustainable development strategy that benefits society and future generations. In this study, a semi-industrial ultrafiltration (UF) pilot plant established at the outlet of a wastewater treatment plant was studied to assess its feasibility and sustainability for non-potable water reuse. The optimization of operating conditions made it possible to support reliable and sustainable filtration performance, the operating conditions were optimized through comparative analysis in terms of water quality, permeability variation, irreversible fouling management, and water recovery rate. The best conditions were J80t40BW1/3 (flux of 80 L•h -1 •m -2 , filtration cycle time of 40 min, 1 air backwash followed by 3 classical backwashes), J60t60BW1/4 and J60t60BW1/3. The long-term study on condition J60t60BW1/3 provides sustainable and adaptable filtration performance regardless of the temperature and feed water quality variation. In addition, the air backwashes enabled excellent reversibility of membrane fouling, which was approximately 1.25 to 2 times higher than of classic backwashes in average. The quality of the UF permeate was good enough to be reused in non-potable purposes as it met reuse guidelines of the World Health Organization, reuse standards of France, and the most recent EU regulation for agricultural irrigation. A specific study of membrane cleaning has shown that the addition of NaClO in backwash water can greatly increase cleaning efficiency of air backwashes. Finally, the calculation of the capital expenditure (CAPEX) and operational expenditure (OPEX) of the UF system under optimized conditions gives a profitable net unit price for water production. Through this thesis, UF is confirmed to be a reliable tertiary treatment for water reuse and the results give operational indications for the industrial scale and provides proposals for the management of membrane fouling by air backwash with chemical assistance.

Keywords: Ultrafiltration, water reuse, fouling control, air backwash, reuse standard

Réutilisation de l'eau par ultrafiltration en tant que traitement tertiaire d'eaux usées urbaines à l'échelle semi-industrielle -Résumé

La réutilisation de l'eau, dans le cadre d'un développement durable est nécessaire pour la société et pour les générations futures. Dans cette étude, une unité d'ultrafiltration (UF) semi-industrielle placée en sortie de station d'épuration a été étudiée pour évaluer sa faisabilité et sa durabilité. L'optimisation des conditions opératoires a permis de donner pour la première fois des contraintes d'exploitations fiables et durables qui se dégagent par une analyse comparative de l'impact de 15 conditions opératoires différentes sur la qualité de l'eau, la variation de perméabilité, la gestion du colmatage irréversible et le taux de conversion de l'eau. Les meilleures conditions ont été J80t40BW1/3 (flux de 80 L•h -1 •m -2 , durée du cycle de filtration de 40 min, 1 rétrolavage essoré suivi de 3 rétrolavages classiques), J60t60BW1/4 et J60t60BW1/3. Une étude sur du long terme avec la condition J60t60BW1/3 a fourni des performances de filtration durables et adaptables quelles que soient la température et la qualité de l'eau d'alimentation. De plus, les rétrolavages essorés à l'air ont permis une excellente réversibilité du colmatage des membranes, qui était d'environ 1,25 à 2 fois supérieure celle des rétrolavages classiques en moyenne. La qualité du perméat d'UF a été suffisamment bonne pour être réutilisée dans des applications non potables car elle répond à la meilleure qualité des directives de réutilisation de l'Organisation mondiale de la santé, aux normes de réutilisation de la France et à la réglementation européenne la plus récente pour l'irrigation agricole. Une étude spécifique du nettoyage des membranes a permis de montrer que l'utilisation de chlore pouvait avoir une efficacité accrue lorsqu'il est couplé à l'effet mécanique des rétrolavages essorés. Finalement, le calcul des dépenses d'investissement (CAPEX) et opérationnelles (OPEX) du système d'UF donne, dans les conditions optimisées, un prix unitaire net de production d'eau rentable. Au travers de cette thèse, l'UF apparaît comme un traitement tertiaire fiable pour la réutilisation de l'eau et les résultats donnent des indications opérationnelles pour l'échelle industrielle et des propositions pour la gestion du colmatage des membranes par rétrolavage à l'air assisté chimiquement.

Mots clés : Ultrafiltration, réutilisation de l'eau, contrôle du colmatage, retrolavage à l'air, normes de réutilisation

1 2

 12 Introduction

1. 1 .

 1 Definition of water reuse from urban wastewater, applications and regulations 1.1.1

1 TSS: 3 -

 13 9 mg•L -1 COD: 42-103 mg•L -1 PO4-P: 0.8-3.4 mg•L -1 NH4-N: 4.0-33 mg•L -1 Norg: 2-5 mg•L -1

1 UV254

 1 UV254 nm: 0.148-0.155 UV210 nm: 1.579-3.207 TOC: 6.0-8.0 mg•L -1 COD: 12-13 mg•L -1 Mg 2+ : 8.9-9.8 mg•L -1 Ca 2+ : 25.0-28.4 mg•L -1 EC: 631-894 μS•cm -

1 UV254

 1 UV254 nm: 0.148-0.155 UV210 nm: 1.579-3.207 TOC: 6.0-8.0 mg•L -1 Mg 2+ : 8.9-9.8 mg•L -1 Ca 2+ : 25.0-28.4 mg•L -1 EC: 631-894 μS•cm -mg•L-1 Si: 11.7 mg•L -1 Turbidity: 0.6 NTU E. coli: 2.8 × 10 5 CFU•100 mL -1 Virus: 97 PFU•100 mL-1

  be developed in Chapter 3, the filtration performances of two flat sheet membranes and a hollow fibre UF membrane with molecular weight cut-off of 30 kDa,100 kDa and 200 kDa respectively, are first compared in lab. The detailed information of membranes is listed in Table2-2. The material of the three membranes is polyethersulfone (PES). The flat sheet membranes are conducted with the 500 mL Amicon stirred cell with concentrate volume of 420 mL as shown in Figure2-1(a). Hollow fibre membrane is operated with the vertical module with inside membrane volume of 1.9 mL as shown in Figure2-1 (b). These tests are operated under same TMP of 0.3bar and the same feed water. The initial membrane permeability was measured for the three membranes and as expected, the highest MWCO exhibited the highest initial permeability. The experiments were all operated in dead-end filtration mode whatever the geometry of membrane.

Figure 2 - 1 No

 21 Figure 2-1 Filtration instruments in lab (a) flat sheet membrane, (b) hollow fibers

Figure 2 - 2 Figure 2 - 3

 2223 Figure 2-2 Diagram of semi-industrial pilot plant

  3 shows the detailed information of the UF module and membrane. The module is operated in dead-end filtration mode with an inside-out configuration. The best range of operational transmembrane pressure (TMP) on UF should be less than 1 bar. The hydraulic resistance of new membrane modules was measured with pure water to be 4×10 11 m -1 at 20°C (pure water permeability = 900 L•m -2 •h -1 •bar -1 ). The maximum permeability of UF membrane when filtrated with the feed water could reach 700 L•m -2 •h -1 •bar -1 at 20°C and the average value is 600 L•m -2 •h -1 •bar -1 at 20°C. Therefore, each filtration condition was started from initial Lp at around 600 L•m -2 •h -1 •bar -1 , and the corresponding membrane resistance of 6 ×10 11 m -1 at 20°C was considered for future calculations.

  real temperature, a chemical enhanced backwash (CEB) was conducted. A CEB starts with a CB with chlorine, followed by chemical injection which includes the top injection and bottom injection. Next, pilot plant closes all the valves and membrane soaking happens with chemicals to degrade foulants. Chemicals are either sulfuric acid ([H + ] =1000 mg•L -1 ), or sodium hydroxide ([OH -]=800 mg•L -1 ) and chlorine ([Cl2] =50 mg Cl2•L -1 ). The duration of soaking is 1200 s. After soaking, the system discharges the soaking solutions by gravity and then starts with a long-term CB without chlorine until pH of discharge water comes back to a neutral value. The duration and the volume of water used during a CEB is respectively 1560 s and 250 L.

  [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF]. The total 15 different filtration conditions were separated into 3 main groups to study the impact of filtration cycle time, flux, and backwash sequence on membrane filtration performance, such as permeate quality, permeability, fouling reversibility by backwash, fouling resistance, economic costs……. Each filtration condition was conducted continuously for more than 40h. After each operating condition, several CEBs were operated manually to remove the membrane fouling until the initial permeability (Lp) reached about 600 L•m -2 •h -1 •bar -1 , so as to maintain the similar initial membrane state for the next filtration conditions. In chapter 5, the optimized condition based on the results of chapter 3 was selected: a flux of 60 L•h -1 •m -2 , a filtration time of 60 min and an AB frequency of 1/3. The variable in chapter 5 is the chlorine concentration in backwash water. Four backwash conditions were investigated in this test, shown in Table 2-7. Each condition was conducted continuously for 5-7 days to obtain stable filtration performance. To be noted, the parameters including flux and Lp, that could be affected by the temperature have been normalized to a standard temperature (20℃) to account viscosity fluctuations with these parameters.

  Flux (J) (L•h -1 •m -2 ) Filtration time t (min)Backwash sequence (Air Backwash/ Classic Backwash)

  𝐹𝑒𝑒𝑑 -Tur 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 ) 𝑑𝑉 0 ∫(Tur 𝐵𝑊 -Tur 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 ) 𝑑𝑉 𝐵𝑤 × 100% = (Tur 𝐹𝑒𝑒𝑑 -Tur 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 )×J×S×t (Tur 𝐵𝑊 -Tur 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 )×∆𝑉 𝐵𝑊 × 100% (13) 𝐹𝑒𝑒𝑑 -TOC 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 ) 𝑑𝑉 0 ∫(TOC 𝐵𝑊 -TOC 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 ) 𝑑𝑉 𝐵𝑤 × 100% = (TOC 𝐹𝑒𝑒𝑑 -TOC 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 )×J×S×t (TOC 𝐵𝑊 -TOC 𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 )×∆𝑉 𝐵𝑊 × 100%

1

 1 Principle of the analysis and main detection parametersThe detection of microplastics in this study was achieved by the PerkinElmer FT-IR spectrometer with spectrum Spotlight 400 FT-IR microscope (USA). During this thesis and in partnership with PerkinElmer, the development of this analytical technique was carried out. Therefore, this study was realized from tests on ultrapure water to the identification and quantification of microplastics in seawater treatment plants, pharmaceutical wastewater treatment plants, together with the samples from the WWTP in Chateauneuf-les-Martigues. The analytical process includes sample preparation, digestion of organic matters, filtration, identification and quantification of microplastics, and finally to calculate the removal rate of microplastic particles under different treatment process. The full information will be presented in another scientific paper and not in this thesis because of the relevance and continuity of the subject content. Only the detection of microplastics in the feed and permeate of the UF plant will be presented. The detection system is mainly composed of four parts: the FT-IR spectrometer, the spectrum Spotlight 400 FT-IR microscope, the stage control for sample view movement in automatic and manual, and the computer for data treatment, shown in Figure2-4. The core component of FT-IR spectrometer is the Michelson interferometer that can generate an interferogram by making measurements of the signal at many discrete positions of the moving mirror. The light beam uses the middle IR in this FT-IR spectroscopy with wave number ranges from 400 to 4000 cm -1 that mainly focused on molecular vibrational energy levels (~80 to 8000 cm -1 ). The related software here is Spectrum IMAGE. The computer conducts Fourier transform calculations on the interferogram and displays the spectrum as absorbance (A) or transmittance (T) versus wavenumber. In microscope, the detector is a liquid nitrogen cooled MCTs (LN-MCTs) with high sensitivity on smaller particles (<10 μm). Every day before starting to analyze samples, the MCT detector was refilled with liquid nitrogen to cooldown during prolonged use.

Figure 2 - 4

 24 Figure 2-4 The microscopic-equipped FT-IR spectroscopy system

Figure 2 - 5 2 . 8 . 2 .

 25282 Figure 2-5 Filtration apparatus -vacuum büchner funnel

3- 1

 1 uses the "permeate volume/filtration area" to replace the commonly used volumetric concentration factor (VCF) as the X axis. Y axis reflects flux variation with the ratio of the instantaneous flux to the initial flux, where Jp is the instantaneous permeate flux during filtration, J0 is the initial permeate flux. Overall, the three curves show similar decreasing trend on flux changes during filtration by different membranes when filtrating the same feed water. During filtration, permeability of UF membranes decreased from rapidly to gradually versus permeate volume because of the inevitable membrane fouling[START_REF] Katsoufidou | A study of ultrafiltration membrane fouling by humic acids and flux recovery by backwashing: Experiments and modeling[END_REF].

Figure 3 - 1

 31 Figure 3-1 Permeability variation of UF membranes at different MWCOs

Figure 3 - 2

 32 Figure 3-2 Fouling resistance formation on different membranes.

Figure 3 - 3

 33 Figure 3-3 Example of raw wastewater flowrate and feed water turbidity variation throughout the day and night

Figure 3 - 5 .

 35 Figure 3-5. The variation of permeability was shown in highly-positive correlated trend with the feed water temperature variation from Figure 3-5. The liquid viscosity is decreased with

  to be removed, and the feed water temperature. Except specific weather influence, each experiment suffered the almost same change of feed water quality, flow rate, and temperature variation throughout experiments. Therefore, it was considered that the different experiments at different operating conditions presented in the next sections could be compared.

Figure 3 - 4 3 Figure 3 - 5

 34335 Figure 3-4 Permeability and feed water turbidity variations in condition J60t20BW1/3

Figure 3 - 6

 36 Figure 3-6 Permeability variation versus time in J60t60BW1/3:(a) the whole filtration process, (b) a selected zoomed period

Figure 3 -

 3 Figure 3-7 (a)(b)(c)(d) shows the permeability variation in 4 representative conditions J30t30BW1/3, J60t40BW1/3, J80t40BW1/3, and J80t60BW1/3, respectively. It is more obvious to observe the significance of AB during filtration in conditions J60t40BW1/3, J60t60BW1/3, and J80t40BW1/3, compared to J30t30BW1/3 and J80t60BW1/3. Through comparison of the four

Figure 3 - 7

 37 Figure 3-7 Permeability variation in conditions: (a) J30t30BW1/3, (b) J60t40BW1/3, (c) J80t40BW1/3, (b) J80t60BW1/3

  and/or longer backwash interval can convert more solids, particles and organic matters, into cake fouling resistance over a filtration cycle. To evaluate the influence of flux and filtration cycle time, conditions with gradual increase of filtration cycle time (t) at flux of 60 L•m - 2 •h -1 (or 80 L•m -2 •h -1 ), and with gradual increase of filtration flux (J) at constant t of 30 min (or 60 min) were designed and tested as shown in Table2-6. The average fouling reversibility by CB and AB obtained under different filtration cycle time and different flux conditions with all over 40 hours of operation is shown in Figure 3-8, which is indicative of the overall backwash effectiveness.

Figure 3 - 8

 38 Figure 3-8 Fouling reversibility by CB and AB in different conditions

Figure 3 - 9

 39 Figure 3-9 Resistances' variations versus time at conditions of (a) J60t20BW1/3, (b) J60t60BW1/3 and (c) J100t30BW1/3

  in conditions of J60t60BW1/3 and J80t40BW1/3 which resulted in 92.7% and 94.5% water recovery, respectively. In addition, the soft conditions showed the lowest recovery rates between 70.7% and 72.2% because of frequent AB and CB, and low flux. The water recovery rates of harsh conditions J100t30BW1/3 and J80t60BW1/3, were at an intermediate level, ranging from 84.7% to 89.9%. Except the conditions in backwash frequency of 1/3, the conditions J60t60BW1/4 and J80t60BW1/4, resulted in water recovery rates of 92.8% and 90.8% respectively (not shown in the Figure3-10). The condition J60t60BW1/4 showed almost the same water recovery rate with J60t60BW1/3, with only 0.1% difference because of different permeate consumption between AB and CB. Therefore, the higher water recovery rates among these conditions were obtained from the conditions of J80t40BW1/3, J60t60BW1/4, and J60t60BW1/3 with potential to be the optimized operating conditions in this study. Apart from filtration time and flux, ABs were operated in this study and the AB frequency can have an impact of UF hydraulic performance as discussed in the next section.

Figure 3 -

 3 Figure 3-10 Water reuse recovery rate: conditions at backwash frequency of 1/3. The uncertainty of each column is between 1 and 2%.

  -11 and Figure 3-12, two main variations can be described. On one hand, Figure 3-11 with AB frequency of 1/9 and no AB presents very high (Rirr/Rm)n/(Rirr/Rm)initial increase with turbidity integration and 2 CEBs occurring during 2 days of filtration. On the other hand, Figure 3-12 with AB frequencies of 1/3, 1/4 and 1/6 where (Rirr/Rm)n/(Rirr/Rm)initial slowly increased with turbidity integration. AB frequency in conditions of BW1/3, BW1/4 are the best with excellent Rirr removal abilities, which can maintain membrane permeability over 200 L•m -2 •h -1 •bar -1 in 2 days of filtration. No CEB occurred in these

Figure 3 -Figure 3 -

 33 Figure 3-11 Variation of irreversible resistance as a function of the integral of turbidity vs. time for different BWs (1/9 and No AB) at flux=60 L•m -2 •h -1 and t = 60 min

Figure 3 -Figure 3 -

 33 Figure 3-13 Permeability variation in winter from 26/2/2020 to 18/3/2020

  in the field, the findings indicate that secondary wastewater treatment can contribute to decrease SARS-CoV-2 concentration in wastewater, and tertiary treatment or disinfection enhance the inactivation of SARS-CoV-2 in WWTPs [278-281]. Bogler et al. (2020) stated briefly in their review that SARS-CoV-2 should be removed reliably by UF. Based on the above analysis and detection, the UF permeate after UF treatment in this test has no infectivity of SARS-CoV-2 and can be reused safely. Besides, in order to fully assess UF as a barrier to SARS-CoV-2, lower detection limits in PCR should be sought or new analytical tools should be developed to quantity infectious SARS-CoV-2 for example.

Figure 4 - 1 Figure 4 - 2

 4142 Figure 4-1 Spectra map of ultrapure water with all particles by siMPle (a) pixel size at 6.25 μm (b) pixel size at 25 μm

Figure 4 - 3

 43 Figure 4-3 UF feed deposits on 3 μm filter under different digestion duration by H2O2 (a) 50mL net UF feed after 1d digestion (b) 50mL net UF feed after 7d digestion (c) 50mL net UF feed after 10d digestion (d) 100mL net UF feed after 10d digestion

Figure 4 - 4

 44 Figure 4-4 Spectra map of detected particles distribution in case (a) by siMPle software

Figure 4 - 5 1 Figure 4 - 6

 45146 Figure 4-5 Dimensions distribution of microplastics in municipal WWTP samples

Figure 5 - 1

 51 Figure 5-1 Permeability, feed water turbidity and temperature variation versus time in different backwash conditions

3

  CB is similar to performing an AB. The addition of NaOCl in CB showed an advantage on Rirr control from the beginning of the filtration compared to the previous conditions NNNN and NNNY. The variation of Rirr fluctuated slight around the overall irreversible fouling trendline with periodic ups and downs in YYYN which may be due to the periodic peak and trough periods of influent flow, secondary effluent quality, and temperature during a day as stated in Chapter 3.

Figure 5 - 2

 52 Figure 5-2 Fouling resistance variation versus time in different backwash conditions

Figure 5 -

 5 3 gives the reversibility of AB and 3 rd CB ranges in different conditions and Table5-2 shows the comparison between them. It can be confirmed that AB has dominant position in reversibility compared to CB with or without NaOCl, even the addition of 10 mg Cl2•L -1 NaOCl in CB could not reach the reversibility of AB without NaOCl. Moreover, condition NNNY offered the highest average reversibility of AB (133 ± 16%) and the stable reversibility range (98%-174%), and the second highest was condition YYYY. YYYN is resulted in the lowest AB reversibility. The addition of 10 mg Cl2•L -1 NaOCl in AB improved the reversibility of AB by 15%-18% in average through comparison in parallel conditions NNNN and NNNY, and in conditions YYYN and YYYY.However, the addition of 10 mg Cl2•L -1 NaOCl in CB improved the reversibility of 3 rd CB by 5% in average through comparison in parallel conditions NNNN and YYYN, and the 3 rd CB reversibility in condition NNNY and YYYY was very close to each other. The lowest reversibility of AB in condition YYYN may be because of the highest reversibility of 3 rd CB compared to the other conditions and/or the lack of chlorine. The cleaning performance of CB and AB mutually restricts and influences each other as the reversibility in percentage is related to the previous filtration cycle. From the fouling resistance distribution in section 5.1.2, the Rirr

Figure 5 - 3

 53 Figure 5-3 Reversibility ranges of AB and 3rd CB in different conditions

Figure 5 - 4 Figure 5 - 5

 5455 Figure 5-4 Reversibility of AB versus Rirr on the membrane just before AB

  3 shows the water quality of AB, 3 rd CB, UF feed, and UF permeate in the middle of filtration in different conditions and Figure 5-6 (a) and (b) are the turbidity and TOC removal rates by AB and 3 rd CB through mass balance in a filtration cycle.

Figure 5 -

 5 Figure 5-6 (a) shows that the percentage of turbidity recovered by 3 rd CB is always below 80% which indicated there would be an increased foulant deposition of this residual turbidity after CB together with the new turbidity accumulation for the next filtration cycle. The turbidity removal capacity by 3 rd CB was improved by 15%-30% with 10 mg Cl2•L -1 NaOCl addition

Figure 5 -

 5 Figure 5-6 (a) Turbidity removal rates of AB and 3 rd CB (b) TOC removal rates of AB and 3 rd CB

  backwash condition in this study mainly due to less consumption of NaOCl, sustainable and adaptable filtration performance, and less potential damage on the physicochemical characteristics of membrane. Therefore, the condition NNNY is recommended for long-term operation. The influence of NaOCl concentration on backwash cleaning will be discussed in the next part.

Figure 5 - 7

 57 Figure 5-7 Variation of Rirr-end of filtration cycle (n) to the initial cycle (1) a function of the integral of turbidity vs. time

Figure 5 - 8

 58 Figure 5-8 Cumulative costs for CAPEX and OPEX

system hydraulic filtration performance. 15 filtration

 15 conditions were conducted for investigation of flux and filtration time, and all conditions were shown in constant and stable variation of permeability for 40 hours. While filtrating with real secondary effluent from WWTP, the overall permeability decreased and stabilized to a smaller value with an increased flux and/or filtration time. In constant flux mode, the increase of flux (related to a higher TMP on membrane) and the increase of filtration time both lead to more potential foulants brought onto the membrane. Based on the filtration performances, these conditions were classified into 3 types: soft conditions with lower flux or frequent backwash (short filtration time) resulting in too little productivity and which were discarded. Harsh conditions with higher flux or longer filtration time were also discarded because of high occurrence of CEB which led to difficult permeability stabilization and high consumption of permeate and chemicals. Finally, standard conditions J80t40BW1/3, J60t60BW1/4, and J60t60BW1/3 stood out from the others with higher overall performances based on the comparison of AB and CB reversibility, irreversible fouling resistance increase, occurrence of

  Air backwash frequency on filtration performance. The air injection process in AB greatly increased the cake layer removal efficiency compared to CB. Besides, 5ppm NaOCl addition in backwash water of AB of all condition furtherly improved the cleaning efficiency of AB due to the function of disinfection and oxidation. Therefore, AB showed higher reversibility efficiency than CB, which was around 1.25~ 2 times the reversibility of CB in average. By analysing the influence of AB frequency (1/3, 1/4, 1/6, 1/9, and no AB) on irreversible fouling management, the irreversible fouling resistance increased faster with the decrease of AB frequency during operation. AB frequencies of BW1/3 and BW1/4 under constant flux of 60 L•m -2 •h -1 and tc of 60 min showed better permeability recovery and less CEB occurrence during filtration, thus were recommended for long-term filtration test.

  NaOCl -assisted backwashes on membrane fouling management. In this subject, 4 conditions in chronological order are NNNN, NNNY, YYYN, and finally YYYY. N (No) represents a backwash either CB or AB without NaOCl and Y (Yes) represents a backwash either CB or AB with NaOCl . The other parameters for all conditions are 3 CBs followed with 1 AB, under constant flux of 60 L•m -2 •h -1 and tc of 60 min. The addition of NaOCl in backwash water either for AB or CB is confirmed to greatly enhance the backwash cleaning efficiency thus improving the hydraulic filtration performance according to analysis on filtration permeability, fouling resistance distribution, backwash reversibility, and cake layer removal ability. In all conditions, the estimated consumption of NaOCl in 10 years were lower than the amount that causes the damage on membrane materials and structure. Condition NNNY stands out from the others due to better control of Rirr, less NaOCl consumption, sustainable and adaptable filtration performance, and less potential damage on the physicochemical properties of membrane. The secondary best condition is YYYN which resulting in the best fouling control and permeability recovery, but it has higher potential to damage membrane structures under frequent NaOCl addition. Second, in all conditions, there was a positive correlation between fouling reversibility by AB and Rirr increase, and a negative correlation between fouling reversibility by CB and Rirr increase. Besides, CB with NaOCl hardly exceeded the reversibility of AB without NaOCl .

Figure 2 - 1 51 Figure 2 - 2 52 Figure 2 - 3 53 Figure 2 - 4 62 Figure 2 - 5 65 Figure 3 - 1 73 Figure 3 - 2 74 Figure 3 - 3 76 Figure 3 - 4 77 Figure 3 - 5 77 Figure 3 - 6 78 Figure 3 - 7 79 Figure 3 - 8 80 Figure 3 - 9 83 Figure 3 - 84 Figure 3 - 86 Figure 3 - 86 Figure 3 - 88 Figure 3 - 88 Figure 4 - 1 96 Figure 4 - 2 96 Figure 4 - 3 98 Figure 4 - 4 99 Figure 4 - 5 100 Figure 4 - 6 101 Figure 5 - 1 106 Figure 5 - 2 111 Figure 5 - 3 113 Figure 5 - 4 115 Figure 5 - 5 115 Figure 5 - 6 117 Figure 5 - 7 119 Figure 5 - 8

 21512252235324622565317332743376347735773678377938803983384386386388388419642964398449945100461015110652111531135411555115561175711958 Figure 2-1 Filtration instruments in lab (a) flat sheet membrane, (b) hollow fibers .................. 51 Figure 2-2 Diagram of semi-industrial pilot plant ...................................................................... 52 Figure 2-3 Picture of pilot plant ................................................................................................. 53 Figure 2-4 The microscopic-equipped FT-IR spectroscopy system .......................................... 62 Figure 2-5 Filtration apparatus -vacuum büchner funnel .......................................................... 65 Figure 3-1 Permeability variation of UF membranes at different MWCOs ............................... 73 Figure 3-2 Fouling resistance formation on different membranes. ............................................ 74 Figure 3-3 Example of raw wastewater flowrate and feed water turbidity variation throughout the day and night ........................................................................................................ 76 Figure 3-4 Permeability and feed water turbidity variations in condition J60t20BW1/3 .......... 77 Figure 3-5 Permeability and feed water temperature variations in condition J60t20BW1/3 ..... 77 Figure 3-6 Permeability variation versus time in J60t60BW1/3:(a) the whole filtration process, (b) a selected zoomed period ...................................................................................... 78 Figure 3-7 Permeability variation in conditions: (a) J30t30BW1/3, (b) J60t40BW1/3, (c) J80t40BW1/3, (b) J80t60BW1/3 ................................................................................ 79 Figure 3-8 Fouling reversibility by CB and AB in different conditions .................................... 80 Figure 3-9 Resistances' variations versus time at conditions of (a) J60t20BW1/3, (b) J60t60BW1/3 and (c) J100t30BW1/3 ........................................................................ 83 Figure 3-10 Water reuse recovery rate: conditions at backwash frequency of 1/3. The uncertainty of each column is between 1 and 2%. ........................................................................ 84 Figure 3-11 Variation of irreversible resistance as a function of the integral of turbidity vs. time for different BWs (1/9 and No AB) at flux=60 L•m -2 •h -1 and t = 60 min .................. 86 Figure 3-12 Variation of irreversible resistance as a function of the integral of turbidity vs. time for different BWs (1/3, 1/4, and 1/6) at flux=60 L•m -2 •h -1 and t = 60 min ................ 86 Figure 3-13 Permeability variation in winter from 26/2/2020 to 18/3/2020 .............................. 88 Figure 3-14 Permeability variation in Summer from 1/7/2020 to 27/7/2020 ............................. 88

Table 1 -

 1 2 Constituents present in wastewater with their associated risks[START_REF] Pasquini | Occurrence of eight household micropollutants in urban wastewater 140 and their fate in a wastewater treatment plant[END_REF][START_REF] Touraud | Drug residues and endocrine disruptors in drinking water: Risk for humans?[END_REF][START_REF] Henze | Wastewater treatment: biological and chemical processes[END_REF][START_REF] Marcos Von | Wastewater characteristics, treatment and disposal[END_REF].

	Wastewater Constituents	Contents	Risks
	Microorganisms	Pathogenic bacteria, viruses and worms' eggs	Risk when exposed to humans and animal by inhalation or drinking
		Pesticides, pharmaceuticals,	Environmental as well as further
	Micropollutants	fuel additives, cyanotoxins, personal care products,	expected impacts on humans, such as genotoxic, immunotoxic, carcinogenic
		detergents	and fertility-impairing effects
	Suspended solids	Particles, solids, colloids	Carrying pollutants and pathogens
	Biodegradable	Organic carbon, sugar,	Oxygen depletion in rivers and lakes;
	organic matters	protein, ammonia	fish death; odors
	Other organic	Fat, oil and grease, coloring,	Toxic effect, esthetic inconveniences,
	matters	solvents, phenols	bioaccumulation in the food chain
	Other Nutrients	Nitrogen (ammonium, nitrates), phosphorus	Eutrophication, oxygen depletion, toxic effect
	Metals	Hg, Pb, Cd, Cr, Cu, Ni	Toxic effect, bioaccumulation
	Others inorganic materials	Acids, for example, hydrogen sulfide, bases	Corrosion, toxic effect
	Thermal effects	Hot water	Changing living conditions for flora and fauna
	Odor (and taste)	Hydrogen sulfide	Esthetic inconveniences, toxic effect
	Radioactivity		Toxic effect, accumulation

Table 1 -

 1 3 Water reuse categories and typical application (WHO guidelines and EU Parliament regulation).

	Organization	Category	Typical Application	pH	TSS (mg•L -1 )	Turbidity (NTU)	BOD5 (mg•L -1 )	Residual Cl -(mg•L -1 )	Fecal Coliform (E. coli as an Indicator) (100 mL -1 )
			A		≤10	≤5	≤10		≤ 10 / below detection limit
	EU Parliament	Agriculture irrigation	B C		≤35 Directive	--	≤25 Directive		≤100 ≤1000
					91/271/EEC		91/271/EEC
			D			-			≤10,000
		Agriculture	Food crop irrigation (uncooked)	6-9	ND	≤2	≤10	1	ND
		irrigation	Non-food crops and crops consumed after processing	6-9	≤30	-	≤30	1	≤ 200
		Landscape	Parks; schoolyards; Playgrounds	6-9	ND	≤2	≤10	1	ND
		irrigation	Golf courses; Cemeteries; Greenbelts; Residential	6-9	≤30	-	≤30	1	≤200
		Industrial	Cooling water; boiler feed;	6-9
		recycling and	Process water; Heavy		≤30	-	≤30	-	≤200
		reuse	construction
	WHO guidelines	Groundwater	Groundwater replenishment; saltwater intrusion control;			Site-specific; specific guidelines do not exist.
			Subsidence control
		Recreational Environmental uses	Lakes and ponds; marsh snowmaking enhancement; streamflow augmentation; fisheries;	6-9	ND	≤2	≤10	1	ND
		Non-potable urban uses	Fire protection; air conditioning; toilet flushing	6-9	ND	≤2	≤10	1	ND
			Blending in water supply
		Potable uses	reservoirs; Blending in groundwater; Direct pipe-to-pipe
			water supply

Table 1 -

 1 4 Membrane separation characters for water purification[START_REF] Shon | Nanofiltration for water and wastewater treatment -A mini review[END_REF][START_REF] Abdel-Fatah | Nanofiltration systems and applications in wastewater treatment: Review article[END_REF][START_REF] Asano | Water reuse: issues, technology, and applications[END_REF][START_REF] Nath | [END_REF][START_REF] Dach | Comparaison des opérations de nanofiltration et d'osmose inverse pour le dessalement sélectif des eaux saumatres : de l'échelle du laboratoire au pilote industriel[END_REF].

	Characteristics	MF	UF	NF	RO (low-pressure)
	mechanism Separation	Sieve	Sieve	electric repulsion solution/diffusion, Sieve,	Solution/diffusion,
				Finely porous	Nonporous
	Membrane	Porous	Porous	asymmetric/	asymmetric/compos
				composite	ite
	Molecular weight cut-off	> 300 kDa	1-300 kDa	200-1000 Da	< 200 Da
		Colloids, TSS,
	Retained compounds	turbidity, some protozoan oocysts, cysts, some bacteria and some specific viruses under	Macromolecules , proteins, colloids, bacteria, viruses	LMWC, mono-, di-and oligo-, saccharides; polyvalent anions, viruses some hardness,	LMWC, sodium, chloride, glucose, amino acids, hardness, ions
		conditions
	Transmembrane pressure (TMP)	< 5 bar	< 10 bar	< 20 bar	< 100 bar
		Crossflow	Crossflow
	Flow modes	or	or	Crossflow	Crossflow
		Dead-end	Dead-end

HMWC: high molecular weight compounds; LMWC: low molecular weight compounds.

Table 1 -

 1 5 MF/UF processes alone or combined with pretreatments after secondary treatment for water reuse applications.

	Process
	(Scale and Operation	Feed Wastewater	Operating Conditions	Feed Characteristics	Permeate Quality/Removal Rate	Application for Reuse	Standard Basis	Ref.
	Duration)
	MF (pilot	Domestic wastewater	Capacity: 10 m
	plant, 120 d)	(septic tank
		effluent)

  3

Table 1 -

 1 [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF] Membrane bioreactors (MBR) for water reuse applications.

	Membrane
	Process
	(

Scale and Operating Duration) Operating Conditions Feed Characteristics Permeate Quality/Removal Rate (in Average) Application for Reuse Standard Basis Ref.

		Feed: urban			Directly for
	Aerobic MBR+ GAC (water recycle plant, 12 months) Aerobic MBR (External): Pilot plant for 162 days Vertical submerged MBR (pilot scale for 600 days)	wastewater UF: 0.02 μm/300 kDa Flux: 75-150 L•m -2 •h -1 HRT: 5 d SRT: 5-30 days Feed: Primary effluent of municipal wastewater recycling plant UF: 0.04 μm HRT: 3.2 h (MBR) + 0.58 h (GAC) Feed: municipal wastewater in Korea UF: 0.45 μm Flux: 6.2 L•m -2 •h -1 HRT: 8 h SRT: 60 days	COD: 200-800 mg•L -1 SS: 100-600 mg•L -1 NH3-N: 10-30 mg•L -1 Coliform: 10 5 -10 6 •L -1 Turbidity: 50-70 NTU pH: 7.5-8.5 BOD5: 46.2-262.1 mg•L -1 COD: 142.0-512.0 mg•L -1 SS: 47.5-240 mg•L -1 pH: 7.6 BOD5: 406 mg•L -1 COD: 232 ± 41 mg•L -1 TSS: 220 ± 52 mg•L -1 TN: 42 ± 5 mg•L -1 TP: 3.2 ± 0.4 mg•L -1 Volatile fatty acids: <1.0 47 mg•L -1 Alkalinity as CaCO3: 145 ± pH: 7.3 ± 0.1 mg•L -1	COD: 9.4 mg•L -1 , 97%; SS: nd,100%; NH3-N: 0.2-1.3 mg•L -1 , 96.2%; Turbidity: < 2 NTU Coliform: nd pH: 8.2 BOD5: < 1.9 mg•L -1 , >96% COD:< 48.3 mg•L -1 , >65.9% SS: < 7.2 mg•L -1 , >85% Fecal coliforms: 0.3 CFU•100 mL -1 Phages: 3.9-5.6 log reduction BOD5: 8 ± 4 mg•L -1 , 98% COD: 9.0 ± 3.6 mg•L -1 , 96% TSS: 220 ± 52 mg•L -1 TN: 10.6 ± 2.6 mg•L -1 , 74% pH: 7.3 Turbidity: 0.18 NTU, CFU•mL -1 TP: 0.7 ± 0.2 mg•L -1 , 78% Total colony counts: 24	municipal purposes or indirectly for industrial uses after additional treatment Non-potable Urban or rural reuse, such as washing and car sprinkling toilet flushing,	Water reuse standard of China California Department of Public Health Drinking water WHO and the standards of Korea	[156] [154] [157]
		Feed: black water	Total COD: 1218 mg•L -1	Total COD: 42 ± 8.81 mg•L -1 ,		Water
	Aerobic	from household	Soluble COD: 417 mg•L -1	96%	Toilet	reuse
	submerged MBR (pilot-scale, 50	MF: 0.4 μm Flux: 30-40	TN: 188 mg•L -1 NH4 + -N: 155 mg•L -1	TSS: 2 ± 1.19 mg•L -1 , 99% TN: 19 ± 4.73 mg•L -1 , 89%	flushing, Cleaning,	standards of EPA,	[132]
	days)	L•m -2 •h -1	TP: 21.3 mg•L -1	NH4 + -N: 11 ± 3.76 mg•L -1 , 92%	Irrigation	EU, WHO,
		HRT: 36 h	TSS: 560 mg•L -1	NOX-N: 8 ± 3.1 mg•L -1		Turkey
			Total coliform: >10 6 100	Total coliforms: 0, 100%
			mL -1
	Aerobic submerged MBR (pilot plant, 6 months)	Feed: hotel greywater UF: 0.04 μm, hollow fiber Flux: 20 L•m -2 •h -1	COD: 41-500 mg•L -1 BOD5: 36-295 mg•L -1 TN: 2.6-25 mg•L -1 Ammonia N: 0.3-14 mg•L -1 Total count: 1.5 × 10 7 -4.1 × 10 7 CFU•100 mL -1 Total coliforms: 1.4 -4.1 × 10 6 mL -1 E. coli: < 1.1 × 10 6 CFU•100 CFU•100 mL -1	COD: <36 mg•L -1 TN:<10 mg•L -1 Ammonia N: <8 mg•L -1 Legionella spp.: < 1 CFU•100 mL -1 E. coli: <1.1 × 10 2 CFU•100 mL -1 Total count: 5.8 × 10 3 -1.6 × 10 5 CFU•100 mL -1 Total coliforms: 0.27 × 10 2 -2.1×10 2 CFU•100 mL -1	Non-potable reuse	Spanish standard water reuse	[155]

Table 1 -

 1 7 NF / RO/ FO coupled with pretreatment processes for wastewater reuse applications.

	Process

(Scale and Operation Duration) Feed Water Operating Conditions Feed Characteristics Final permeate quality (Removal rate) Application for Reuse Standard Basis References

				(raw wastewater)
				EC: 1174 ± 2 μS•cm -1 pH: 7.22 ± 0.11 TSS: 488 ± 48 mg•L -1 Turbidity: 248 ± 11 NTU DOC: 126.6 ± 7.3 mg•L -1 COD: 478 ± 132 mg•L -1	EC: 397 μS•cm -1 pH: 8.06 TSS: 0 mg•L -1 Turbidity: 0.23 NTU DOC: 0.35 mg•L -1
				F -: 0.096 ± 0.003 mg•L -1
	Submerged MBR+ NF	Municipal wastewater after primary treatment	UF: 200 kDa, hollow fiber NF: 150-300 Da, TMP: 0.1-0.5 bar (UF); 41 bar	Cl -: 156.0 ± 2.4 mg•L -1 NO2 -: 64.35 mg•L -1 NO3 -: 144.53 ± 42.17 mg•L -1 PO4 3-: 9.631 ± 1.428
			(NF)	mg•L -1
				SO4 2-: 36.33 ± 0.84
				mg•L -1
				Na + : 71.14 ± 0.48 mg•L -1
				K + : 11.85 ± 0.14 mg•L -1
				Mg 2+ : 22.05 ± 0.04
				mg•L -1
				Ca 2+ : 110.7 ± 0.2 mg•L -1
				SAR: 1.61 ± 0.01

Table 1 -

 1 8 Wastewater recovery rate and energy consumption of membrane-based technologies.

	Process	Productivity	Membrane Flux	Recovery Rate	Energy Consumption	Ref.

Table 1 -

 1 [START_REF] Qu | Tertiary treatment of secondary effluent using ultrafiltration for wastewater reuse: correlating membrane fouling with rejection of effluent organic matter and hydrophobic pharmaceuticals[END_REF] Studies on the combined physical backwash with low concentrated oxidants/disinfectants in backwash water

	Backwash types	Concentration	Backwash time × flux or TMP	Filtration time × flux	Feed water	Membrane process (pore size/area)	Remarks	Ref.
	NaOCl-assisted backwash	23.8 mg Cl2•L -1	24 s / (207-241.5 kPa)	(15-30 min) × (34-102 L•m -2 •h -1 )	Tertiary treated wastewater	UF (150 kDa/1.9 m 2 )

Table 2 -

 2 [START_REF] Mudgal | European Commission, Directorate-General for the Environment[END_REF] shows the quality of the inlet and outlet effluent of the WWTP. This outlet effluent was the UF feed of this

work. The atmospheric temperature in Châteauneuf-les-Martigues per year probably ranged from 3℃ to 32 ℃. The temperature of UF feed which is secondary effluent from WWTP was between 15℃ and 26℃, thereby reducing the influence of water temperature on filtration performances.

Table 2 -

 2 1 Raw wastewater and UF feed quality

	Parameters	Campaign 1 (October 2019 -March 2020) WWTP influent Outlet effluent (UF feed)	Campaign 2 (July 2020 -April 2021) WWTP influent Outlet effluent (UF feed)
	E. coli (CFU 100mL -1 )	1.6  10 8	(3.4  2.6)  10 4	> 1.4  10 6	(9.4  8.5)  10
	Enterococci (CFU 100mL -1 )	2.2  10 7	(1.3  1.0)  10 4	(3.4  3.1)  10 7	(9.5  8.6)  10
	Anaerobic sulphito-reducers (spores) (CFU 100mL -1 )	5.6  10 3	268  253	(1.7  1.3)  10 4	(9.6  5.1)  10
	Specific F-RNA bacteriophages (PFP 100mL -1 )	4.5  10 3	< 30	(1.8  1.7)  10 3	< 30
	COD (mgO2•L -1 )	1124	20  9	552  61	45  21
	BOD5 (mgO2•L -1 )	n.m.	n.m.	205  82	< 3
	TSS (mg•L -1 )	77	4  2	367  166	12.1  8
	TOC (mgC•L -1 )	n. m.	18  9	n.m.	n.m.
	Turbidity (NTU)	n. m.	2.3  0.9	208  38	2.1 ± 1.6
	NH4 + (mgN•L -1 )	3.8 ± 2.4	-	3.8 ± 2.4	-
	pH	n. m.	7.2  0.4	7.4  0.3	7.5  0.1
	Conductivity (S•cm -1 )	n. m.	1 168  128	n.m.	n.m.

CFU: colony-forming unit; PFP: Polyhedral, filamentous, and pleomorphic; n. m.: not measured. COD: Chemical oxygen demand; BOD5: Biochemical oxygen demand TSS: Total suspended solids; TOC: Total organic carbon.

Table 2 -

 2 3 UF membrane and module characteristics

	Characteristics	Data
	Material	PES (polyethersulfone)
	Pore size -MWCO	0,02 µm -200 kDa
	Length	1.2 m
	Internal diameter ID	0.9 mm
	Number of channels	7
	Filtration Surface	9 m²
	Volume of fibers	2.0 L
	Maximum TMP	2.5 bar
	pH tolerant value	1-13

Table 2 -

 2

		4 Optimal parameters for classic backwash
	Operating conditions	Optimal range values in	CB parameters in this
		general [19]	study
	Backwash interval	10-60 min	20-60 min
	Backwash duration	10-90 s	52 s
	Backwash strength*	1-5	2.5-5
	Backwash water	Permeate, deionized water	Permeate

Backwash strength*: The ratio of backwash pressure to permeate pressure or the ratio of backwash flux to permeate flux.

To eliminate fouling in this PhD, three types of membrane cleanings were automatically carried out by the pilot. The detailed procedures of CB and AB are shown in

Table 2 -

 2

5 Physical backwash parameters

AB with Cl (RL A1) AB without Cl (RL A2) CB with Cl (RL C1) CB without Cl (RL C2)

	Step 1	Air injection into the fibers (2 min)	Air injection into the fibers (2 min)
	Step 2	Decompression before standard backwash	Decompression before standard backwash	Decompression before standard backwash	Decompression before standard backwash
	Step 3	Backwash top head (31 s)	Backwash top head (31 s)	Backwash top head (31 s)	Backwash top head (31 s)
	Step 4 Backwash 2 heads (3 s) Backwash 2 heads (3 s) Backwash 2 heads (3 s) Backwash 2 heads (3 s)
	Step 5	Backwash bottom head (18 s)	Backwash bottom head (18 s)	Backwash bottom head (18 s)	Backwash bottom head (18 s)
	Step 6	Backwash prefilter (12 s)	Backwash prefilter (12 s) Backwash prefilter (12s)	Backwash prefilter (12 s)
	Permeate tank (volume)	T1 (29.25 L) + T2 (6.75 L)	T2 (36 L)	T1 (29.25 L) + T2 (6.75 L)	T2 (36 L)
	Duration	184 s	184 s	64 s	64 s

Table 2 -

 2 [START_REF] Warsinger | A review of polymeric membranes and processes for potable water reuse[END_REF] Filtration conditions in chapter 3

Table 2 -

 2 [START_REF] Yang | Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-of-the-Art and Performance Analysis[END_REF] Backwash conditions in chapter 5 on condition J60t60BW1/3

		CB	CB	CB	AB	Name
	1	No Cl	No Cl	No Cl	No Cl	NNNN
	2	10 mg Cl2•L -1 Cl	10 mg Cl2•L -1 Cl	10 mg Cl2•L -1 Cl	No Cl	YYYN
	3	No Cl	No Cl	No Cl	10 mg Cl2•L -1 Cl	NNNY
	4	10 mg Cl2•L -1 Cl	10 mg Cl2•L -1 Cl	10 mg Cl2•L -1 Cl	10 mg Cl2•L -1 Cl	YYYY
	2.7. Hydraulic filtration performance of UF
	membrane
	2.7.1. Permeability

Table 2 -

 2 [START_REF] Shi | Role of concentration polarization in cross flow micellar enhanced ultrafiltration of cadmium with low surfactant concentration[END_REF] The types of materials recorded in siMPle and their abbreviations

	No.	Polymer and natural material	Abbreviation in siMPle
	1	Polyethylene	pe
	2	Polypropylene	pp
	3	Polystyrene	ps
	4	Polyamide (Nylon)	pa
	5	Polyvinyl Chloride	pvc
	6	Acrylonitrile Butadiene Styrene	abs
	7	Polyethylene Terephthalate	pet
	8	Polymethylmethacrylate (Acrylic)	pmma
	9	Protein	protein
	10	Polyetheretherketone	peek
	11	Poly Lactic Acid	pla
	12	Ethylene Vinyl Acetate	eva
	13	Polyoxymethylene (Acetal)	pom
	14	Stearate	stearate
	15	Stearate + Glyceride	stearate + glyceride
	16	Polyisoprene	polyisoprene
	17	Polytetrafluoroethylene	ptfe
	18	Cellulose	cellulose
	19	Polyether Block Amide or Polyester	peba
		Block Amide
	20	Silicone	silicone
	21	CaCO3	caco3
	22	Glyceride	glyceride
	23	Wax	wax
	2.8.1.2 Sample preparation
	methods used in this study was H2O2. First, samples can be digested with 30% (w/v)
	H2O2 at a volume ratio of 1:1 for 1-10 days at room temperature. During stirring, the
	glass bottle was covered with aluminum foil to prevent airborne contamination. The
	rinsing water used in this study is ultrapure water. This water was selected after a
	comparison of different clean waters (HPLC water, distilled water, Evian water, tap
	water, etc.).

Sample pretreatment is necessary to be considered before analysis. Pretreatment consists of digestion of organic matters which could hide MPs on the filters. As the composition of the samples can directly affect the digestion methods and duration, it is necessary to find the suitable digestion protocol of each type of water. The digestion

Optimization of UF operating conditions for wastewater reuse 3.1. Introduction

  Santé Environnement Hygiène de Lyon) certified by the French Ministry of Health for water analysis. The methods for COD and BOD5 are respectively ISO 15705 and NF EN ISO-5815-1. and NF EN ISO 7899-2 for Enterococci are used in samples during Campaign 1 with both detection limits at < 1 CFU•100mL -1 . The detection methods NF EN ISO 9308-3 for E. coli, and NF EN ISO 7899-1 for Enterococci are used in samples of Campaign 2 with both detection limits at <56 CFU•100mL -1 . Inlet and outlet (UF feed) of the WWTP and permeate were analysed at the same time.

	As reviewed in Chapter 1, the membrane-based technologies used for municipal wastewater
	treatment for water reuse usually include microfiltration/ultrafiltration (MF/UF)-based
	technologies, membrane biological reactor (MBR) and nanofiltration/forward osmosis/ reverse
	osmosis (NF/FO/RO)-based technologies
	The microbiological analyses were also tested by Carso laboratory and consisted in
	the measurements of E. Coli (NF EN ISO 9308-1, NF EN ISO 9308-3), Enterococci
	(NF EN ISO 7899-1, NF EN ISO 7899-2), anaerobic sulphito-reducers (spores) (NF EN
	26461-2), specific F-RNA bacteriophages (NF EN ISO 10705-1), and SARS-CoV-2 by

real-time quantitative polymerase chain reaction (qPCR). For SARS-CoV-2 analysis, the envelope protein gene E is first tested and the nucleoprotein gene N is tested only if the envelope protein gene E is detected. The detection methods NF EN ISO 9308-1 for E. coli, CHAPTER 3.

Table 4

 4

	-1 shows the

Table 4 -

 4 1 Mean UF feed and permeate qualities compared to WHO guidelines, and French reuse standards for irrigation

	Parameters	Campaign 1 (October 2019 -March 2020) UF permeate Mean  SD RRs* by WWTP+UF (%) RRs* by UF (%)	Mean  SD	Campaign 2 (July 2020-April 2021) UF permeate RRs* by WWTP+UF (%)	RRs* by UF (%)	WHO guidelines	French standard (A)*	European parliament regulation (A) *
	E. coli (CFU•100mL -1 )	< 1	> 6.7 (log*)	> 4.8(log*)	< 56	> 6.5  1.4(log*)	> 2.0  0.5(log*)	≤ 200	≤ 250	≤ 10 / ≥ 5 (log*)
	Enterococci (CFU•100mL -1 )	< 1	> 6.2 (log*)	> 4.4(log*)	< 56	> 5.4 1.4(log*)	> 1.1  0.3(log*)	-	≥ 4 (log*)	-
	Anaerobic sulphito-reducers (spores) (CFU•100mL -1 )	< 1	> 4.1 (log*)	-	< 1	> 3.5  0.3(log*)	> 2.8  0.1(log*)	-	≥ 4 (log*)	≥ 5 (log*) /Absence
	Specific F-RNA bacteriophages (PFP•100mL -1 )	< 1	> 3.6 (log*)	-	< 30	> 2.6  0.8(log*)		-	-	≥ 4 (log*)	≥ 6 (log*) /Absence
	COD (mgO2•L -1 )	< 10	> 98 %	>44%	< 30	> 95.4 2.0%		-	-	< 60	-
	BOD5 (mgO2•L -1 )	-	-	-	< 3	> 98.1 0.3%		-	-	-	≤ 10
	TSS (mg•L -1 )	< 2	> 97%	> 56%	< 2	> 98.5 0.8%		> 84  6%	≤ 30	< 15	≤ 10
	TOC (mgC•L -1 )	4.61  0.61	94 ± 3%	70 11%	-	-		-	-	-	-
	Turbidity (NTU)	0.42  0.35	-	85 7%	< 0.31	> 99.9 0.0%		> 86  11%	≤ 2	-	≤ 5
	pH	7.46  0.07	-	-	7.5  0.1	-		-	-	-	-
	Conductivity(S•cm -1 )	1056  70	-	-	-	-		-	-	-	-
	CFU: colony-forming unit; PFP: Polyhedral, filamentous, and pleomorphic; log*: log removal calculated from the raw wastewater quality; -: not measured.
	(A)*: There are ABCD four different levels of water quality in French water reuse standards and EU regulation. Level A being the best.
	RRs*: Removal rates

. Detection of microplastic particles (MPs) in WWTP effluent and removal by UF 4.2.1. Selection of rinsing water for MP analysis

  To reduce external microplastic contamination, it is necessary to select a qualified water for rinsing during pretreatment and filtration processes described in section 2.8.1.2. In this part, the microplastic particles in Evian water, ultrapure water, distilled water (DW), and tap water were all detected more than twice for comparison. Before each filtration, the glass devices will be first rinsed with ultrapure water and acetone, then rinsed with the tested water before filtration. The distribution of microplastics in different types of water samples under 6.25 μm/pixel is shown in

Table 4 -

 4

2. Each test consisted in filtrating 1 L of sample through the 3 μm gold filter. Except microplastics, all particles shown in Table 4-2 contains mainly protein and cellulose, and a bit of CaCO3 based on siMPle database. During the filtration of the samples through 3 μm gold

Table 4 -

 4 2 Detection results in different types of water

			Particle concentration in each test (Particles•L -1 )		Major	Minor
	Water types	Particles	1	2	3	4	5	6	Average ± SD	Types of MP	dimension of MP (μm)	dimension of MP (μm)
	Ultrapure water	Only MP All particles	11 -	22 -	16 -	38 158 272 205 212±47 40 4 22±3	pe, pp, ps, pa, pet, pvc, silicone	20-150	10-60
	DW	Only MP All particles	31 714	23 498	12 197 825 38			26±10 558±239	pa, pp, ps, pet, pvc, abs, pe, eva, silicone	20-250	10-120
	Evian	Only MP All particles	19 348	2 530	4 171				8±7 350±146	pa, pe, pp, ps, pet	20-200	16-100
	Tap water	Only MP All particles	3 1566 1254 9					6±3 1410±156	ps, pa, pp, pvc 45-80	10-40

Table 4 -

 4 3 The microplastics concentration in quantity and in total surface area of samples from

		municipal WWTP
	Samples	Concentration (MP•L -1 ) (mean ± SD)	Concentration in covered surface area (μm 2 •L -1 ) (mean ± SD)
	UF feed	249 ± 25	(6 ± 2) × 10 5
	UF Permeate	35 ± 5	(2.8 ± 0.3) × 10 4

Table 5 -

 5 [START_REF] Mudgal | European Commission, Directorate-General for the Environment[END_REF] The consumption of NaOCl of each condition in 10 years

		Estimated total CT in	CT of backwash in 10	Equivalent consumption		Maximum
	Name	10 years	years	of NaOCl	CEB frequency	NaOCl CT value
		(mg Cl2•L -1 •h)	(mg Cl2•L -1 •h)	[gCl2•m -3 (permeate)]		of UF module
	NNNN	60 833	0	272	Once per day
	NNNY	15 225	3058	175	Once in 5 days	23853
	YYYN	19 630	9490	414	Once in 6 days	mg Cl2•L -1 •day
	YYYY	24 820	10544	546	Once in 5 days

Table 5 -

 5 2 Reversibility ranges of backwash in different conditions

			3 rd CB			AB
	Conditions
		Min	Max	Mean ± SD	Min	Max	Mean ± SD
	NNNN	76%	102%	91 ± 7%	92%	140%	118 ± 12%
	NNNY	75%	104%	86 ± 8%	98%	174%	133 ± 16%
	YYYN	85%	125%	96 ± 7%	81%	135%	107 ± 12%
	YYYY	64%	114%	87 ± 14%	85%	165%	125 ± 21%

  The slight decline of CB reversibility in conditions NNNN and NNNY was very close to each other and both conditions used non-chlorinated CB for cleaning. The CB of YYYN and YYYY showed higher reversibility with lower Rirr deposition, but the CB reversibility decreased faster with Rirr increase compared to condition NNNN and NNNY. On the one hand, the chlorinated CB offered higher reversibility that could better control Rirr in lower levels. On the other hand, although chlorinated CB was good at Rirr controlling, it has poor adaptability and lower reversibility when Rirr increased.Looking back to NNNN and NNNY, the cleaning efficiency of non-chlorinated CB was more stable and sustainable with Rirr variation. Condition YYYN although had the best fouling resistance management, non-chlorinated AB was resulted in lower reversibility which was much closer to the performance of chlorinated CB. Both conditions YYYN and YYYY showed faster decrease of CB reversibility with Rirr increase. From this point, condition NNNY is more recommended as optimized backwash condition which showed relatively higher effective and stable reversibility variation both of AB and CB compared to other conditions.

		200%
		175%
		150%
	Reversibility	125%			NNNN
		100%			NNNY YYYN
					YYYY
		75%			Liner (NNNN) Liner (NNNY)
					Liner (YYYN)
					Liner (YYYY)
		50%
		0.0E+00	2.0E+11	4.0E+11	6.0E+11	8.0E+11
				R irr before AB

Table 5 -

 5 3 The Turbidity and TOC in different types of backwash water and UF feed and

	permeate

  3

Table 5 -

 5 8 Calculation of energy and chemical costs of filtration

	Codename Parameters	Values	Remarks
	D0	Number of P1	1
	D1	Number of P2	1
	D2	Filtration flow rate	540 L•h -1	Constant
	D3	Filtration time in one cycle	1 h	Set value
	D4	Total filtration duration in a year	8423 h•yr -1	D3=8760h•yr -1 -A1×A8-B1×B2-C1×C2
	D5	Filtration cycles in a year	8423 yr -1	D5=D4/D3
	D6	Flush numbers in one filtration cycle	1
	D7	Flush duration in one filtration cycle	15 s	Set value
	D8	Flush flow rate	2.5 m 3 •h -1
	D9	Feed water volume for flush in a year	88 m 3	D9=D8×D7×D5
	D10	Working flow of feed pump (P1)	2.5 m 3 •h -1
	D11	Workload of P1 per year	4618 m 3	D11=D2×(D3-D7) ×D5+D9
	D12	Working time of P1 per year	1847 h•yr -1	D12=D11/D10
	D13	P1 (feed pump) power	1.00 kW
	D14	Working time of P2 for flush per year	35 h•yr -1	D14=D7×D5
	D15	Working time of P2 for filtration per year	8388 h•yr -1	D15=D4-D14
	D16	P2 power at 540 L•h -1	0.55 kW	Manual
	D17	P2 power at 2.5 m 3 •h -1	0.83 kW	Manual
	D18	Energy consumption of P1 per year	336 €•yr -1	D18=D12×D13×A11
	D19	Energy consumption of P2 per year	845 €•yr -1	D19=(D16×D15+D17×D14) ×A11
	D20	Air compressor working frequency for valves	Once every 10 min Experience value
	D21	Air compressor working time each time for valves 10s	Experience value
	D22	Energy consumption of air compressor for valves 40 €•yr -1	D22=D21×6×8760h•yr -1 ×C6×A11
	D23	Net Permeate production per year	4188 m 3 •yr -1 D23=D2×D15-A1×A2-B1×B3-C1×C5
	$E-filtration	$(Energy consumption of filtration)	1221 ۥyr -1	$E-filtration = D18+D19+D22

Table 5 -

 5 9 Energy consumption of Chemical pumps

	Codename Parameters	Values	Remarks
	E0	Soda pump (P7) working time	5.41 h•yr -1	E0=A3×A1
	E1	Chlorine pump (P8) working time	5.41 h•yr -1	E1=A3×A1
	E2	Acid pump working time	5.41 h•yr -1	E2=A4×A1
	E3	Chlorine pump (P4) working time	60 h•yr -1	Estimated value
	E4	All chemical pumps power	0.03 kW
	$E-cp	$(Energy consumption of chemical pumps) 0.5 €•yr -1	E5=E4×(E0+E1+E2+E3) ×A11

Table 5 -

 5 10 Economic cost

	Type	Cost	Remarks
	$ (UF module replacement)	440 ۥyr -1	Refer to Table 5-4
	$ (chemical consumption)	1323 ۥyr -1	$=$C-CEB + $C-AB
	$ (energy consumption)	1267 ۥyr -1	$=$E-CEB + $E-CB + $E-AB + $E-Filtration + $E-cp
	$ (maintenance + labor)	294 €•yr -1	$= 10% × Depreciation(CAPEX)
	OPEX	3324 ۥyr -1
	CAPEX	2940 ۥyr -1
	Total price	5824 ۥyr -1	Total price=OPEX+CAPEX-$ (UF module replacement)

Unit price of permeate production 1.39 ۥm -3 Unit

price of production=Total price/D23

Table 5 -

 5 [START_REF]Guidelines for the safe use of wastewater, excreta and greywater[END_REF] Expenditure cost on different backwash conditions

		NNNN		NNNY	YYYN	YYYY
	CEB frequency	Once per day	Once in 5 days	Once in 3 days	Once in 6 days	Once in 5 days
	Number of CEB in a year (yr -1 )	365	73	122	61	73
	Number of AB in a year (yr -1 )	2008	2154	6510	2160	2154
	Number of CB in a year (yr -1 )	6388	6534	2130	6540	6534
	NaOCl concentration in backwash water (mg Cl2•L -1 )	0	10	5	10	10
	$E-CEB (ۥyr -1 )	5.8	1.3	2.4	1.1	1.3
	$C-CEB (ۥyr -1 )	3703	741	1238	619	741
	$E-CB (ۥyr -1 )	17	18	17	18	18
	$C-CB (ۥyr -1 )	0	0	0	678	811
	$E-AB (ۥyr -1 )	24	26	26	26	26
	$C-AB (ۥyr -1 )	0	171	85	0	171
	$E-filtration (ۥyr -1 )	1200	1226	1221	1227	1227
	$E-cp (ۥyr -1 )	1.5	2.1	0.5	2	2.1
	$ (chemical consumption) (ۥyr -1 )	3703	912	1323	1297	1723
	$ (energy consumption) (ۥyr -1 )	1246.8	1271.3	1267	1272.1	1272.3
	CAPEX (ۥyr -1 )	2940	2940	2940	2940	2940
	OPEX (ۥyr -1 )	5683.8	2917.3	3324	3303.1	3729.3
	Net production (m 3 )	4023	4221	4188	4230	4222

Unit price of product (ۥm -3 ) 2.03 1.28 1.39 1.37 1.48

  The objective of this thesis was to investigate the feasibility of the UF technology as tertiary treatment for municipal wastewater reuse on non-potable purposes, such as pipe washing, street cleaning, underground water recharge, etc. Meanwhile, the thesis aimed to investigate the influence of filtration parameters such as flux, filtration time, backwash sequence including classical and air backwashes with or without NaOCl on UF membrane filtration performances and fouling management, in order to find out the optimized filtration conditions of the semiindustrial UF pilot system and provide guidance for future industrial application. The assessment of optimums conditions is mainly based on comparison of the permeate quality, water recovery rate, backwash efficiency, fouling control, and capital/operational expenditure. The conclusions are listed as follows.

	Selection

of UF system on wastewater treatment for reuse purpose

. After a large state of the art, ultrafiltration has been successfully applied on industrial scale and wastewater reuse cases around the world. The UF membranes enables high removal efficiency on total suspended solids, turbidity, microorganisms, and partial removal efficiency on organic matters. Generally, UF membranes provide higher removal capacity on contaminants and qualified permeate production compared to MF membranes. UF membranes are less sensitive to fouling formation especially irreversible fouling compared to NF and RO, together with lower requirement on feed water quality, transmembrane pressure, installation and commissioning. Currently, UF process is considered as one of the most cost-effective technology to deal with secondary effluent on nonpotable reuses. Therefore, UF system is suggested in this thesis and a semi-industrial UF pilot plant was installed after the secondary effluent of a French WWTP.

Table 4 -

 4 2 Detection results in different types of water ................................................

Table 4 -

 4 3 The microplastics concentration in quantity and in total surface area of samples from municipal WWTP ................................................................

Table 5 -

 5 1 The consumption of NaOCl of each condition in 10 years .......................

Table 5 -

 5 2 Reversibility ranges of backwash in different conditions .........................

Table 5 -

 5 3 The Turbidity and TOC in different types of backwash water and UF feed and permeate ..............................................................................................

Table 5 -

 5 4 Calculation of CAPEX ..............................................................................

Table 5 -

 5 5 Calculation of energy and chemical costs of CEB ....................................

Table 5 -

 5 6 Calculation of energy and chemical costs of CB.......................................

Table 5 -

 5 7 Calculation of energy and chemical costs of AB ......................................

Table 5 -

 5 8 Calculation of energy and chemical costs of filtration ..............................

Table 5 -

 5 9 Energy consumption of Chemical pumps..................................................

Table 5 -

 5 10 Economic cost .........................................................................................

Table 5 -

 5 11 Expenditure cost on different backwash conditions ................................

MOULIN

respectively. These conditions with low flux or low filtration time had the smallest filtrated volume and initial TMP as well as no CEB needed during 40 h operation. Consequently, these conditions are referred as soft conditions. Some other conditions, such as J80t60BW1/3, J80t60BW1/4, and J100t30BW1/3, were resulted in relatively weaker removal ability of CB and AB. These conditions with high flux or high filtration time were also the only conditions where at least 5 CEBs were needed during 40 hours of operation. Thus, these conditions are referred as harsh conditions.

Despite the soft and harsh conditions, the rest is considered as standard conditions with CB reversibility ranging between 80% and 90%, and AB reversibility ranging between 120% and 145%. The harsh conditions of J80t60BW1/ 3, J80t60BW1/4 could filtrate the highest volume (720 L) during one cycle which also means the large quantity of fouling load would be retained by membranes. The highly increased fouling resistance thereby reduced the fouling reversibility of CB and AB. This phenomenon can be explained by the higher filtration volume over a filtration cycle (Vs-cyc) as a combined result of flux and time, which means more solids, particles and organic matters retained by membrane thus increasing both irreversible and reversible fouling.

For J100t30BW1/3 condition, even if the total filtrated volume in a cycle Vf-cyc (450 L) was lower than in standard conditions (such as J60t60BW1/3 and J80t40BW1/3), the reversibility of both CB and AB were still lower, and with more frequent CEBs. According to Darcy's law, the increase of flux (100 L⋅m -2 ⋅h -1 ) under constant filtration cycle time can directly increase TMP CHAPTER 4. Impact of UF on water quality estimated the costs of UF for another application and for the size of the pilot plant used.

Operating Expenses (OPEX) is the day-to-day cost for running a product, business, or system.

Costs related to replacing consumables (e.g., ultrafiltration membranes), consumption of chemicals and/or energy, the maintenance, and the labor were taken into account for the OPEX in this study. UF pilot plant and UF module lifespan are estimated at 10 years, but modules are considered to be changed every 5 years to ensure the good condition of the membranes. Capital expenditure (CAPEX) is determined as the depreciation of the fixed assets, including the cost of the investment and the UF modules. The following budget calculation was firstly based on 1 pilot plant and 1 UF membrane module under the optimized condition J60t60BW1/3 with 5 mg Cl2•L -1 NaOCl addition in AB water. The flow rate for one UF membrane module is 540L

The equation of CAPEX can be translated as follows:

CAPEX= $ (pilot plant) + $ (UF module)

Table 5-4 shows the related factors and costs of CAPEX. In industrial production, a set of spare membrane module needs to be bought in case of special conditions occurrences. The final CAPEX of the project is 2940 ۥyr -1 . To calculate maintenance and labor costs, a value equivalent to 10% of the fixed capital expenditure was considered [START_REF] Guilbaud | Economic viability of treating ballast water of ships by ultrafiltration as a function of the process position[END_REF][START_REF] Weschenfelder | Oilfield produced water treatment by ceramic membranes: Bench and pilot scale evaluation[END_REF]. The cost for UF module replacement [$ (UF module replacement)] is calculated the same as $ (UF module) in CAPEX as shown in Table 5-4. The process to generate OPEX is mainly focused on CEB cleaning, AB, CB, filtration process, and pumps. Table 5-5-Table 5-9 listed the practical information of the above processes for energy and chemical cost calculation. The calculation process and method were presented in the remarks of Tables, but the unit conversion was not included. The chemical consumption includes the use of 14% NaOCl solution, 30% NaOH solution and 50% H2SO4 solution. The consumption of 30%

NaOH solution and 50% H2SO4 solution was related to the quantity of chemicals used in CEB.

The consumption of NaOCl was calculated at the ideal state with total usage in CEB (50 mg Cl2•L -1 ) and air backwash (5 mg Cl2•L -1 ). The potential consumption of NaOCl was not taken into account which includes the complex reaction with ammonia or ammonium compounds in permeate, self-decomposition and chlorine gas volatilization, and usage in manual cleaning of equipment. The consumption of energy was mainly from pumps and air compressor used in cleaning processes, filtration process, and chemical injection process. The consumption of energy all was converted into cost of electricity. In conclusion, the pilot plant in condition J60t60BW1/3 with 5 mg Cl2•L -1 NaOCl addition in air backwash was resulted in CAPEX of 2940 €•yr -1 and OPEX of 3324 €•yr -1 . The net price of unit production in this study is 1.39 €•m - 3 to implement UF as tertiary treatment in semi-industrial scale for water reuse. It is clear that this cost would be much lower at industrial scale thanks to economy of scale.

Conclusions and Perspectives

List of Tables