Grégorio Crini
email: gregorio.crini@univ-fcomte.fr

Cesare Cosentino
email: cosentino@ronzoni.it

Corina Bradu
email: corina.bradu@g.unibuc.ro

Marc Fourmentin
email: marc.fourmentin@univ-littoral.fr

Giangiacomo Torri
email: torri@ronzoni.it

Olim Ruzimuradov
email: ruzimuradov@rambler.ru

Idil Arslan-Alaton

Maria Concetta Tomei
email: tomei@irsa.cnr.it

Ján Derco
email: jan.derco@stuba.sk

Mondher Barhoumi

Helena Prosen
email: helena.prosen@fkkt.uni-lj.si

Borislav N Malinović
email: borislav.malinovic@tf.unibl.org

Martin Vrabeľ
email: martin.vrabel@stuba.sk

Mohammad Mahmudul Huq

Jafar Soltan
email: j.soltan@usask.ca

Eric Lichtfouse
email: eric.lichtfouse@inrae.fr

Nadia Morin-Crini

Advanced treatments for the removal of alkylphenols and akylphenol polyethoxylates from wastewater

Keywords: Alkylphenols, Alkylphenol polyethoxylates, Wastewater, Removal technologies, Advanced treatments, Ozonation, Adsorption, Granular activated carbon, Cyclodextrin polymers, Clays, Molecularly imprinted polymer, Biodegradation, Sequential anaerobic-aerobic digestion, Microalgae, Constructed wetlands, Phenolic root exudates, Advanced oxidation processes, Electrochemical degradation, Photocatalysis, Zero-valent iron, Catalytic oxidation, Nanomaterials

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Alkylphenols and mainly their polyethoxylate derivatives, alkylphenol polyethoxylates, are used in a variety of applications and consumer products, e.g. paints and latex paints, adhesives, inks, formulation of pesticides, paper industry, textile and leather industry, petroleum recovery chemicals, metal working fluids, personal care products, washing agents, cleaners and detergents. By far the two most commercially important alkylphenols are nonylphenol and octylphenol, which are used primarily to produce nonylphenol polyethoxylates and octylphenol polyethoxylates, respectively. Due to their widespread use, alkylphenols and alkylphenol polyethoxylates, particularly nonylphenol, are ubiquitous in the environment [START_REF] Ying | Environmental fate of alkylphenols and alkylphenol ethoxylates -a review[END_REF][START_REF] Gultekin | Synthetic endocrine disruptors in the environment and water remediation by advanced oxidation processes[END_REF][START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF] and are found in various compartments such as rivers, freshwater, coastal and marine ecosystems, sediments, soils, sewage sludge, and the atmosphere [START_REF] Corvini | Microbial degradation of nonylphenol and other alkylphenols: our evolving view[END_REF][START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF][START_REF] David | Alkylphenols in marine environments: distribution monitoring strategies and detection considerations[END_REF][START_REF] Bergé | Meta-analysis of environmental contamination by alkylphenol[END_REF]. The occurrence of these substances in aquatic environments is mainly correlated with the discharge of effluents from sewage treatment plants and from industry [START_REF] Langford | Fate and behavior of endocrine disrupters in wastewater treatment processes[END_REF][START_REF] Corsi | Nonylphenol ethoxylates and other additives in aircraft de-icers, anti-icers, and waters receiving airport runoff[END_REF][START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF]. The literature on alkylphenols and alkylphenol polyethoxylates is extensive (Table 4.1).

Nonylphenol is persistent in the aquatic environment and extremely toxic to aquatic organisms. Its dominant source in the environment is (partial) biodegradation of nonylphenol polyethoxylates rather than direct discharges, as industrial discharges are strictly controlled from a regulatory point of view [START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF]. Nonylphenol ethoxylates in domestic wastewater reach the sewage treatment plant where microorganisms progressively decompose the ethoxy chain to finally release several compounds including the nonylphenol that was initially used to synthesize the detergents. These substances are readily biodegradable under aerobic or anaerobic conditions in the environment. They are then found in water or adsorbed on sediment. Though less toxic than nonylphenol, nonylphenol polyethoxylates are also highly toxic to aquatic organisms. More generally, alkylphenol polyethoxylates are unstable and both undergo the same processes of degradation to yield metabolites that are generally more stable and thus more persistent. It is known that not only the parent molecules but also their degradation products or metabolites represent a potential ecotoxicological problem in aquatic systems. In addition, these emerging compounds exert endocrine disruption effects since they mimic natural hormones by interacting with estrogen receptors [START_REF] Naim | Tritium radioactivity in the aquatic environment over Alexandria region, Egypt[END_REF][START_REF] Claisse | Review of "emerging" organic contaminants in biosolids and assessment of international research priorities for the agricultural use of biosolids[END_REF][START_REF] Cocchieri | Total tin and organotin in seawater from the gulf of Naples, Italy[END_REF][START_REF] Smith | Adsorptive selectivity of organic-cation-modified bentonite for non-ionic organic contaminants[END_REF][START_REF] Ginsberg | Environmental oestrogens[END_REF]). Humans are exposed to alkylphenols by the intake of contaminated foods and drinking water. Nonylphenol and octylphenol present in plastic containers and wrappings may migrate into foods and drinking water. Another route of human exposure includes contact with personal care products and detergents. Nonylphenol has been detected in human milk, blood, and urine (Table 4.1).

Because of their ubiquitous occurrence in the environment and their high toxicity, alkylphenols and their derivatives constitute a major concern for all the national (e.g., French Water Agency), European (European Agency) and international (US EPA) institutions involved in water management. Over the last 20 years, European legislation on wastewater discharges has become increasingly strict, particularly in France, where nonylphenols and octylphenols and their polyethoxylate derivatives are the target of action campaigns (e.g., in France with RSDE action -Research and Reduction of Substances in Water; first circular of May 7, 2007). These substances are among the 70 priority substances and their use has been restricted since 2013 (Directive 2003/53/EC, 2003). In the European Water Framework Directive (2013/39/CE), nonylphenols (in particular 4-(para)-nonylphenol)) and octylphenols (para-tert-octylphenol) are classified as priority hazardous substances and priority substances, respectively [START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF]). Thus, these substances have been monitored in industrial discharge waters with the aim of reducing or eliminating them (with an elimination target for each industrial company for November 2021, December 2028 or August 2033, depending on the concerned substance). The industrial sector must therefore mobilize to eliminate or reduce these substances. However, the problem is not simple because it is difficult to remove trace contaminants from complex mixtures of substances [START_REF] Crini | Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment[END_REF]Badot 2007, 2010). Moreover, their elimination is not systematically targeted in industrial treatments. Domestic discharges are also affected but the existing conventional water treatment plants used to treat these discharges have not been designated for these emerging contaminants. In this context, it is necessary to propose and develop various efficient technologies for the elimination of alkylphenols from water and wastewater that are efficient, economically viable, technologically simple, and without environmental impact. This is what has been motivated the scientific community for the past 20 years. The European Union has also established maximum concentrations at 0.3 μg/L for 4-(para)-nonylphenol and 0.1 μg/L for para-tert-octylphenol in inland waters. For nonylphenol, the US EPA guide on quality of drinking water recommends a maximum concentration of 28 μg/L for fresh water.

After general and brief considerations on alkylphenols and alkylphenol polyethoxylates, this chapter presents recently proposed advanced technologies for their removal including adsorption-oriented processes, biotechnological methods, membrane bioreactor technology, and advanced oxidation methods. Selected works have been highlighted to present research and discuss these technologies.

General Considerations on Alkylphenols

Applications

Alkylphenols and alkylphenol polyethoxylates are synthetic molecules that, in spite of their high cost, are used in numerous industrial, agricultural, and household applications. This is due to their different and important roles. They can act for instance as detergents, emulsifiers, wetting agents, dispersants, antistatic agents, demulsifiers, (heat) stabilizers, or solubilizers. They were used primarily as surfactants in detergents. These substances can also be used as curing agents or as chemicals to make phenolic resins or to produce plastics [START_REF] Möbius | Surfactants: chemistry, interfacial properties, applications[END_REF][START_REF] Lorenc | Alkylphenols. Kirk-Othmer encyclopedia of chemical technology[END_REF][START_REF] Kayama | Potential health effects of alkylphenols in Japan[END_REF][START_REF] Pradyot | Part II, Chapter 21: Air analysis[END_REF][START_REF] Kovarova | Alkylphenol ethoxylates and alkylphenols -update information on occurrence, fate and toxicity in aquatic environment[END_REF].

Indeed, alkylphenols and alkylphenol polyethoxylates have been used for more than 50 years, being important for industrial activities such as the cleaning industry, textiles, coatings, metallurgical industry, adhesives, pesticide formulation, pulp and paper, oils and fuels, construction materials, and the plastic industry [START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF]. They also found use in cosmetics and personal care products, the synthesis of flavors and antioxidants, the production of fragrances and stabilizers, the processing of rubber for the manufacture of tires, printing inks, the paint industry, electrical insulation varnishes, veterinary medicine formulations, the civil engineering and construction industry, and leather auxiliaries. However, international bans on the use of certain substances and/or restrictions are now in place, particularly in the Europe. Indeed, European legislation (directive 2003/53/EC), in force since 2005, now prohibits the use of nonylphenol and its polyethoxylate derivatives as dispersing agents. Specific exceptions are still granted for certain applications. Despite strict regulations, alkylphenols continue to be found in European rivers and streams, as well as in industrial discharges [START_REF] Crini | Alkylphénols et rejets de la filière traitement de surface (in French)[END_REF].

Chemistry

In general, the term of alkylphenols (abbreviated to APs in the literature) is used to refer to two groups of compounds: nonylphenols (NPs) and octylphenols (OPs). Figure 4.1 gives their general molecular structure. From a structural chemistry point of view, these molecules include numerous isomers. Among the nonylphenols, the nine-carbon nonyl group may be linear or branched and bind at various locations around the phenol ring (ortho, meta and para), and this can be a source of confusion concerning the precise identity of the substance. Nonylphenol is not a single chemical structure (Fig. 4.2): it is a mixture of highly branched nonylphenols, largely mono-substituted in the para-position, with small amounts of ortho-and disubstituted nonylphenols. Also it includes branched C8 and C10 alkyl groups [START_REF] Reed | Alkylphenols[END_REF][START_REF] Seidel | Kirk-Othmer Encyclopedia of chemical technology[END_REF]. Other structures such as propyl-, butyl-, pentyl-, hexyl-and octyl-phenols are also possible. Theoretically, technical nonylphenol consists of a mixture of 211 possible constitutional isomers with a highly branched alkyl chain and 50-80 isomers that can exist in appropriate environmental matrices [START_REF] Guenther | Estrogen-active nonylphenols from an isomer-specific viewpoint: a systematic numbering system and future trends[END_REF]. Much of the literature refers to linear or normal nonylphenols, often the specific para region-isomer, i.e. 4-n-nonylphenol or para-nonylphenol (Fig. 4.1).

The term of alkylphenol polyethoxylates (APnEOs) also refers to two groups of substances, nonylphenol polyethoxylates (NPnEO) and octylphenol polyethoxylates (OPnEO). However, their structure is more complicate because these substances are composed of a branched alkylphenol (nonylphenol or octylphenol) coupled to a polyether chain consisting of ethylene oxide units [START_REF] Vazquez-Duhalt | Nonylphenol, an integrated vision of a pollutant. Scientific review[END_REF][START_REF] Guenther | Estrogen-active nonylphenols from an isomer-specific viewpoint: a systematic numbering system and future trends[END_REF][START_REF] Gultekin | Synthetic endocrine disruptors in the environment and water remediation by advanced oxidation processes[END_REF][START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF][START_REF] Vega Morales | Determination of alkylphenol ethoxylates and their degradation products in liquid and solid samples[END_REF]. Alkylphenol polyethoxylates are manufactured by reacting branched olefins with phenol in the presence of an acid catalyst under basic conditions. The structure of NPnEO is depicted in Fig. 4.1 where n is the average number of moles of ethylene oxide per mole of nonylphenol, ranging from 1 to 100. The degree of ethoxylation depends on the molar ratio of nonylphenol to olefin (ethylene oxide in this case). The nonylphenol polyethoxylate most commonly used in cleaning agents uses n = 9 (NP9EO). In addition, for nonylphenol polyethoxylates surfactants, there are also several other nomenclatures such as nonoxynol, nonylphenol polyglycol ether, nonylphenoxy[poly(ethylenoxy)] ethanol or α-(nonylphenyl)-ωhydroxy-poly(oxyethylene). In all cases, it is important to use the information given by the manufacturers and the Chemical Abstract Service (CAS registry names and numbers) for a complete and clear identification of the substances used. CAS number 84852-15-3 corresponds to the most widely produced nonylphenol, branched 4-nonylphenol, and referred to in the literature as 4-nonylphenol, para-nonylphenol or p-nonylphenol. Table 4.2 and Fig. 4.2 show the CAS numbers for several nonylphenols, octylphenols, nonylphenol polyethoxylates and octylphenol polyethoxylates, and their molecular structures, respectively [START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF].

Nonylphenol is considered to be a hydrophobic molecule with a relatively high partition coefficient compared to others (Table 4.2), making it poorly soluble. As such, it preferentially associates with suspended solids. Water solubility is directly proportional to n [START_REF] Ahel | Bioaccumulation of the lipophilic metabolites of nonionic surfactants in freshwater organisms[END_REF][START_REF] Ying | Environmental fate of alkylphenols and alkylphenol ethoxylates -a review[END_REF]. Its value is the number of polar groups forming the hydrophilic part of the molecule. Lower oligomers (<5) are described as water-insoluble or lipophilic whereas the higher oligomers are water-soluble or hydrophilic. The solubilities of octylphenol monoethoxylate and octylphenol diethoxylate are significantly greater than those of nonylphenol monoethoxylate, nonylphenol diethoxylate and nonylphenol (Table 4.2), indicating the predominant influence of the hydrophobic chain length on alkylphenol polyethoxylates solubility. The low partition coefficient for alkylphenol polyethoxylate (logK ow values in Table 4.2) suggests that these substances may become associated with organic matter in sediments. For this reason, alkylphenol polyethoxylates and their degradation products (including alkylphenols and/or metabolites such as Fig. 4.2 Molecular structures of some alkylphenols (NP nonylphenols, 4-n-NP linear paranonylphenol, 4-NP para-nonylphenols, 4-tert-OP para-octylphenol, NP1EO nonylphenol monoethoxylates, NP2EO nonylphenol diethoxylates, OP1EO octylphenol monoethoxylates, OP2EO octylphenol diethoxylates)

Alkylphenols and the Aquatic Environment

Since the late 2000s, numerous reviews and articles have reported the presence of nonylphenol and octylphenol in all aquatic environments, i.e. in oceans, estuaries, coastal lagoons, lakes, rivers, surface waters, groundwater, and other sources of potable water (Table 4.1). Their occurrence in these environments is mainly correlated with the discharge of effluents from sewage treatment plants and from industry [START_REF] Langford | Fate and behavior of endocrine disrupters in wastewater treatment processes[END_REF][START_REF] Corsi | Nonylphenol ethoxylates and other additives in aircraft de-icers, anti-icers, and waters receiving airport runoff[END_REF][START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF]. Numerous studies evaluating the presence and concentrations of alkylphenol polyethoxylates and their metabolites have also been published on their ubiquitous distribution in sewage treatment plant discharges, industrial discharge waters and living organisms [START_REF] Gultekin | Synthetic endocrine disruptors in the environment and water remediation by advanced oxidation processes[END_REF]. Although partial elimination or degradation/biodegradation is observed in sewage treatment plants and industrial treatment plants, these discharges are nevertheless an important source of contamination. It is also recognized that industrial discharge waters (surface treatment industry, textile sector, etc.) are another important input of these substances into the aquatic environment. Following input into receiving waters, the more persistent alkylphenols tend to accumulate in sediments [START_REF] Ying | Environmental fate of alkylphenols and alkylphenol ethoxylates -a review[END_REF]). An input to the environment was the direct application of pesticide formulations containing nonylphenol. Alkylphenols can also be bind strongly to soil following applications of sewage sludge to agricultural land. In indoor air, a source of alkylphenols was building materials, due to their use as antioxidants for polymer resins.

In Europe (European Commission 2013, 2015, 2018), environmental quality standards have been proposed for priority substances to provide a benchmark for achieving the good surface water chemical status that EU member states are required to respect. The environmental quality standards for nonylphenol and octylphenol in water surface were proposed at 0.3 μg/L and 0.1 μg/L, respectively [START_REF] David | Alkylphenols in marine environments: distribution monitoring strategies and detection considerations[END_REF]). However, environmental quality standards are still not harmonized worldwide. The US EPA developed chronic criterion recommendations for nonylphenol, whereby its concentration should not exceed 6.6 μg/L in freshwater and 1.7 μg/L in saltwater [START_REF] Brooke | Glutathione biosynthesis plays an important role against 4-tert-octylphenol-induced oxidative stress in Ceratophyllum demersum[END_REF]. Much higher values were found not only in the European aqueous compartments but also in North America and Asia [START_REF] Sole | Estrogenicity determination in sewage treatment plants and surface waters from the Catalonian area (NE Spain)[END_REF][START_REF] Bester | Nonylphenols, nonylphenol-ethoxylates, linear alkylbenzenesulfonates (LAS) and bis(4-chlorophenyl)-sulfone in the German Bight of the North Sea[END_REF][START_REF] Petrovic | Endocrine disruptors in sewage plants, receiving river waters, and sediments: integration of chemical analysis and biological effects on feral carp[END_REF][START_REF] Oros | Surveillance for previously unmonitored organic contaminants in the san Fransico estuary[END_REF][START_REF] Li | Seasonal flux of nonylphenol in Han River, Korea[END_REF][START_REF] Shao | Nonylphenol and nonylphenol ethoxylates in river water, drinking water, and fish tissues in the area of Chongqing, China[END_REF][START_REF] Vazquez-Duhalt | Nonylphenol, an integrated vision of a pollutant. Scientific review[END_REF][START_REF] Jackson | Sources of endocrine-disrupting chemicals in urban wastewater, Oakland, CA[END_REF][START_REF] David | Alkylphenols in marine environments: distribution monitoring strategies and detection considerations[END_REF][START_REF] Bergé | Meta-analysis of environmental contamination by alkylphenol[END_REF][START_REF] Kovarova | Alkylphenol ethoxylates and alkylphenols -update information on occurrence, fate and toxicity in aquatic environment[END_REF][START_REF] Crini | Alkylphénols et rejets de la filière traitement de surface (in French)[END_REF].

In rivers, lakes and streams, nonylphenol concentrations can range from below detection levels to highs of >600 μg/L, depending on various factors such as season, river flow and sedimentation, which influence the rate of (bio)degradation. In general, the results for surface waters present seasonal variations with higher concentrations in the summer due to an increase in microbial activity with warmer temperatures leading to an enhanced degradation of nonylphenol ethoxylates. It was suggested that a microbial activity at warmer temperatures leads to an enhanced biodegradation of nonylphenol and octylphenol as well as photolysis induced by sunlight can influence alkylphenol concentration in the surface layer of natural waters during summer [START_REF] Kovarova | Alkylphenol ethoxylates and alkylphenols -update information on occurrence, fate and toxicity in aquatic environment[END_REF]. [START_REF] Li | Seasonal and spatial distribution of nonylphenol and IBP in Saemangeum Bay, Korea[END_REF] found nonylphenol concentrations in Saemangeum Bay (Korea) below detection levels to 298 μg/L with high levels in summer season. [START_REF] Song | Field survey of environmental estrogen pollution in the coastal area of Tokyo Bay and Nagasaki City using the Japanese common goby Acanthogobius flavimanus[END_REF] recently reported a value of 1100 ng/L in seawater in Tokyo Bay (Nagasaki City, Japan). [START_REF] Oros | Surveillance for previously unmonitored organic contaminants in the san Fransico estuary[END_REF] and [START_REF] Jackson | Sources of endocrine-disrupting chemicals in urban wastewater, Oakland, CA[END_REF] reported detection of nonylphenol at 0.004 ng/L in a single water sample and 0.024-6.25 μg/L in water samples from San Francisco Bay. Concentrations in the ng/L range in Minnesota lakes without wastewater treatment effluents were reported. [START_REF] Xu | Tracking major endocrine disruptors in coastal waters using an integrative approach coupling field-based study and hydrodynamic modeling[END_REF] reported concentrations of nonylphenol in a Chinese river water and sediment (Pearl River Delta Guangzhou) of 5.05 µg/L and 14.40 µg/L, respectively. Nonylphenol concentrations measured for estuaries and coastal areas were much lower than those of certain freshwater sites receiving sewage inputs [START_REF] David | Alkylphenols in marine environments: distribution monitoring strategies and detection considerations[END_REF]. [START_REF] Saeed | Sources and levels of endocrine disrupting compounds (EDCs) in Kuwait's coastal areas[END_REF] reported concentrations of alkylphenol in coastal waters and sediments in Kuwait with levels of a few ng/L and ng/g, respectively. A few measurements of alkylphenols in rain water have been undertaken [START_REF] Bergé | Meta-analysis of environmental contamination by alkylphenol[END_REF]. Nonylphenol concentrations in rain water and snow were found to reach between 0.03 and 1.20 μg/L, suggesting that wet deposition must be considered as a major source of nonylphenol in the environment. The presence of alkylphenols in industrial wastewaters is less well-documented [START_REF] Berryman | Nonylphenolic compounds in drinking water and surface waters downstream of treated textile and pulp and paper effluents: a survey and preliminary assessment of their potential effects on public health and aquatic life[END_REF][START_REF] Bergé | Meta-analysis of environmental contamination by alkylphenol[END_REF][START_REF] Sancey | Décontamination des effluents de traitement de surface par oxydation/ bioadsorption sur cyclodextrine (in French)[END_REF][START_REF] Crini | Alkylphénols et rejets de la filière traitement de surface (in French)[END_REF]. [START_REF] Bergé | Meta-analysis of environmental contamination by alkylphenol[END_REF] indicated industrial nonylphenol levels in the 0.13-200 μg/L range, i.e., twice as high as levels in residential wastewater. [START_REF] Crini | Alkylphénols et rejets de la filière traitement de surface (in French)[END_REF] reported nonylphenol concentrations in the <0.1-102 μg/L range discharge waters from surface treatment industries. Following an inter-laboratory study, the authors highlighted the high variability of the results and the difficulty of analyzing these molecules in complex matrices. In Europe, if an industry is confronted with alkylphenols and alkylphenol polyethoxylates in its discharges, it must put in place actions to eliminate or reduce them, but there are not yet specific regulations.

From an ecotoxicological point of view, the estrogenicity of alkylphenols such as nonylphenol and octylphenol has been highlighted in fish [START_REF] Ahmadpanah | Effects of nonylphenol on hematological parameters and immune responses in immature rainbow trout (Oncorhynchus mykiss)[END_REF][START_REF] Sayed | Immunotoxic effects of 4-nonylphenol on Clarias gariepinus: cytopathological changes in hepatic melanomacrophages[END_REF], aquatic invertebrates [START_REF] Hart | Effect of 4-nonylphenol on the immune response of the Pacific oyster Crassostrea gigas following bacterial infection with Vibrio campbellii[END_REF][START_REF] Guo | Accumulation and depuration of nonylphenol and its effect on the expressions of vitellogenin and vitellogenin receptor in freshwater prawn Macrobrachium rosenbergii[END_REF]) and plants (Cahyanurani et al. 2017;[START_REF] Cheng | Bioaccumulation, growth performance, and transcriptomic response of Dictyosphaerium sp. after exposure to nonylphenol[END_REF]. For example for fish, nonylphenol is hepatotoxic [START_REF] Abd-Elkareem | Hepatotoxic responses of 4-nonylphenol on African catfish (Clarias gariepinus): antixoidant and histochemical biomarkers[END_REF], hemotoxic [START_REF] Ahmadpanah | Effects of nonylphenol on hematological parameters and immune responses in immature rainbow trout (Oncorhynchus mykiss)[END_REF], histopathological [START_REF] Shirdel | Effects of nonylphenol on key hormonal balances and histopathology of the endangered Caspian brown trout (Salmo trutta caspius)[END_REF], genotoxic [START_REF] Sharma | 4-Nonylphenol induced DNA damage and repair in fish, Channa punctatus after subchronic exposure[END_REF][START_REF] Sayed | Sensitivity of medaka (Oryzias latipes) to 4-nonylphenol subacute exposure; erythrocyte alterations and apoptosis[END_REF], immunotoxic [START_REF] Sayed | Immunotoxic effects of 4-nonylphenol on Clarias gariepinus: cytopathological changes in hepatic melanomacrophages[END_REF], and reproductive toxic [START_REF] Watanabe | Medaka extended one-generation reproduction test evaluating 4-nonylphenol[END_REF][START_REF] Saravanan | Long-term exposure to waterborne nonylphenol alters reproductive physiological parameters in economically important marine fish[END_REF].

Adsorption-Oriented Processes to Remove Alkylphenols from Wastewater

Due to their widespread use in our everyday applications, chemicals, including socalled emerging substances, are ubiquitous in the environment. The list of emerging substances is particularly long and includes pesticides, pharmaceuticals, cosmetics, personal care products and industrial products such as alkylphenols and alkylphenol polyethoxylates. In recent years, many substances have been classified as priority or priority hazardous substances because of their potential effects on human health [START_REF] Ribeiro | An overview on the advanced oxidation processes applied for the treatment of water pollutants defined in the recently launched Directive 2013/39/EU[END_REF]. The problem is not only the variety of these compounds and their harmful and toxic effects, but also their low concentrations in the environment and the fact that most substances are recalcitrant and persistent. These facts pose new challenges for the scientific community [START_REF] Luo | A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment[END_REF]. From a water engineering perspective, however, the challenge is not simple, as it is difficult to remove trace contaminants from complex mixtures of substances (co-occurrence of multicontaminants in mixed wastes, variability of the pH of the effluents, important salinity, etc.) by conventional methods used in municipal wastewater treatment plants, drinking water treatment plants and industrial water treatment plants. However, the water treatment industry has to deal with these substances and integrate these problems into their management, due to increasingly strict regulations.

The most common process in municipal wastewater treatment plants is biological treatment using activated sludge [START_REF] Qiang | Degradation of endocrine-disrupting chemicals during activated sludge process[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF]. This conventional treatment is often insufficient to remove most organic pollutants. Indeed, published research results have shown that municipal wastewater treatment plants are the largest local source of release of priority substances and pollutants to the environment due to the low removal efficiency of many of these compounds [START_REF] Shao | Nonylphenol and nonylphenol ethoxylates in river water, drinking water, and fish tissues in the area of Chongqing, China[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF][START_REF] Eggen | Reducing the discharge of micropollutants in the aquatic environment: the benefits of upgrading wastewater treatment plants[END_REF][START_REF] Qiang | Degradation of endocrine-disrupting chemicals during activated sludge process[END_REF]. [START_REF] Shao | Nonylphenol and nonylphenol ethoxylates in river water, drinking water, and fish tissues in the area of Chongqing, China[END_REF] have previously reported that only half of the total amount of pollutants is removed in conventional wastewater treatment plants by removal or adsorption on sludge. Currently, the purification performance is >90%, but the discharges still contain a cocktail of substances.

Among publications focusing on the practical application of pollutant removal technologies, work to extend existing municipal wastewater treatment plants to other tertiary processes or final treatments dominates [START_REF] Vazquez-Duhalt | Nonylphenol, an integrated vision of a pollutant. Scientific review[END_REF][START_REF] Soares | Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters[END_REF][START_REF] Basile | Review of endocrine-disrupting-compound removal technologies in water and wastewater treatment plants: an EU perspective[END_REF][START_REF] Garcia-Rodríguez | The ability of biologically based wastewater treatment systems to remove emerging organic contaminants -a review[END_REF][START_REF] Ribeiro | An overview on the advanced oxidation processes applied for the treatment of water pollutants defined in the recently launched Directive 2013/39/EU[END_REF][START_REF] Grandclement | From the conventional biological wastewater treatment to hybrid processes, the evaluation of organic micropollutant removal: a review[END_REF]). The concept is to use a final or tertiary treatment to remove the remaining pollutants produced during secondary biological treatment. The concept is to use final or tertiary treatment to remove the remaining pollutants produced during secondary biological treatment. The technology involves the implementation of integrated processes that are a combination of two or more treatment methods that are intended to be complementary [START_REF] Grandclement | From the conventional biological wastewater treatment to hybrid processes, the evaluation of organic micropollutant removal: a review[END_REF]. For example, the addition of activated carbon can increase the removal of poorly biodegradable organic compounds through adsorption [START_REF] Alvarino | The potential of the innovative SeMPAC process for enhancing the removal of recalcitrant organic micropollutants[END_REF]. This addition of a final treatment step can optimize the efficiency of biological treatment plants and significantly reduce the release of pollutants into the environment. However, the use of tertiary treatment in Europe is not yet widespread for reasons of economic viability, although it may be necessary in the future if further restrictions are applied. In fact, there are two main policies with regard to water pollution control: the first is to focus on reducing pollutant emissions at source (e.g., France) and the second is to focus on downstream reduction at treatment plants (e.g., Switzerland, Germany).

The main tertiary treatments used to date at some industrial sites are activated carbon adsorption, advanced oxidation such as ozonation, and membrane filtration (ultrafiltration, reverse osmosis) [START_REF] Jones | Questioning the excessive use of advanced treatment to remove organic micropollutants from wastewater[END_REF][START_REF] Hollender | Elimination of organic micropollutants in a municipal wastewater treatment plant upgraded with a full-scale post-ozonation followed by sand filtration[END_REF][START_REF] Cases | Endocrine disrupting compounds: a comparison of removal between conventional activated sludge and membrane bioreactors[END_REF]. Each treatment has its own constraints not only in terms of cost, but also in terms of feasibility, efficiency, practicability, reliability, environmental impact, sludge production, operation difficulty, pre-treatment requirements and the formation of potentially toxic byproducts. For example, the advantages for membrane filtration often cited are: large range of commercial membrane available from several manufacturers, small space requirement, simplicity and efficiency, production of a high-quality treated wastewater, no chemicals required and well-known separation mechanisms. The main disadvantages are: investment costs, high energy requirements, high maintenance and operation costs and rapid membrane clogging. Another problem of membrane processes is the formation of separate contaminant concentrates (retentate), which needs to be further investigated. The advantage of chemical oxidation processes, including ozone-based processes, is that they can lead to total mineralization of organic matter into carbon dioxide and water, or to the transformation of hydrophobic organic compounds into more polar, biodegradable compounds [START_REF] Kralchevska | UV-and visible-light assisted photocatalytic oxidation of a pesticide over TiO2 catalysts modified with neodymium and nitrogen[END_REF]. The processes are also integrated physicochemical methods, simple, rapid and efficient. Another advantage is the fact that ozone is generated on-site (no storage-associated dangers). The main disadvantages are: chemicals required, pretreatment indispensable of the effluent, formation of (unknown) intermediates, no significant diminution of chemical oxygen demand, and generation of sludge.

Alkylphenol Removal onto Activated Carbons

Activated carbons are one of the oldest and most widely used adsorbents for adsorbing contaminants from drinking water sources (e.g. rivers, lakes or reservoirs) and for removing pollutants from wastewater streams (e.g. effluents from the textile, pharmaceutical, food and beverages, and petroleum refining industries). Activated carbon technology is indeed widely used on an industrial scale to eliminate pollution in order to obtain water quality that meets regulatory requirements. For example, in a drinking water treatment plant, the large-scale treatment sequence consists of coagulation/flocculation, flotation clarification, sand filtration, disinfection, activated carbon filtration and post-chlorination. In industrial wastewater treatment, carbon technology is used either in secondary treatment or in tertiary treatment after chemical and/or biological operations.

The wide use of activated carbons in industry for liquid phase applications is due to their relatively low cost compared to other materials, their specific characteristics (inert nature, hydrophobic and organophilic, stable in a wide pH range), their high availability, their versatility (products in granular, powdered or fiber forms) and above all their high efficiency (in the >90-99% range) in adsorption-oriented processes. This capacity is mainly due to their structural characteristics and porous texture which gives them a large surface area (500-1500 m 2 /g for liquid phase applications), and their chemical nature which can be easily modified by chemical or thermal treatment in order to vary their properties. Activated carbon technology is also simple and flexible and can be easily integrated into a water treatment plant [START_REF] Dąbrowski | Adsorption of phenolic compounds by activated carbon -a critical review[END_REF][START_REF] Crini | Traitement et épuration des eaux industrielles polluées[END_REF][START_REF] Çeçen | Activated carbon for water and wastewater treatment. Integration of adsorption and biological treatment[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF].

At the industrial scale, they are used to eliminate organic matter, inorganic and organic contaminants (dyes, metals, pesticides, aromatics, rare earth elements, radionuclides, etc.), to decrease chemical oxygen demand and biochemical oxygen demand, to discolor water, and to treat substances that cause a taste or smell. Since the 1980s, activated carbons have also been proposed to remove alkylphenols and alkylphenol ethoxylates [START_REF] Singer | Adsorption of alkyl phenols by activated carbon[END_REF]. Abundant data have been published on this topic [START_REF] Iwasaki | Adsorption of alkylphenols onto microporous carbons prepared from coconut shell[END_REF][START_REF] Tanghe | Adsorption of nonylphenol onto granular activated carbon[END_REF][START_REF] Dąbrowski | Adsorption of phenolic compounds by activated carbon -a critical review[END_REF][START_REF] Crini | Traitement et épuration des eaux industrielles polluées[END_REF][START_REF] Yu | Adsorption of selected pharmaceuticals and an endocrine disrupting compound by granular activated carbon. 1. Adsorption capacity and kinetics[END_REF][START_REF] Çeçen | Activated carbon for water and wastewater treatment. Integration of adsorption and biological treatment[END_REF][START_REF] Tsyntsarski | Removal of detergents from water by adsorption on activated carbons obtained from various precursors[END_REF][START_REF] Katsigiannis | Removal of emerging pollutants through granular activated carbon[END_REF][START_REF] Mailler | Removal of a wide range of emerging pollutants from wastewater treatment plant discharges by micro-grain activated carbon in fluidized bed as tertiary treatment at large pilot scale[END_REF][START_REF] Jeirani | Adsorption of emerging pollutants on activated carbon[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF][START_REF] Vatankhah | Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent[END_REF]. [START_REF] Iwasaki | Adsorption of alkylphenols onto microporous carbons prepared from coconut shell[END_REF] reported that alkylphenols had very high adsorbability by microporous activated carbon having high specific surface area (carbon prepared from coconut shell, powder with specific surface area ranging from 500 to 1800 m 2 /g). The amount of 4-nonylphenol adsorbed at equilibrium concentrations above 20 μg/L increased with activation time as prolongation of the latter increases micropore volume and specific surface area. The amount adsorbed at 1 μg/L increased with activation time from 0.5 to 2.5 h, but decreased from 2.5 to 4.5 h. This decrease under prolonged activation was attributable to the effect of decreased dispersion force through pore enlargement being greater than the effect of increased specific surface area. The authors observed that, in both alkylphenols with linear alkyl chains and those with branched alkyl chains, the amount adsorbed increased with the number of carbon atoms. The amount of alkylphenols adsorbed at equilibrium concentrations above 10 μg/L was higher for alkylphenols with linear alkyl chains of 5-7 carbon atoms than for those with branched alkyl chains of 8-9 carbon atoms due to the molecular sieving effect of the latter. [START_REF] Iwasaki | Adsorption of alkylphenols onto microporous carbons prepared from coconut shell[END_REF] concluded that activated carbons were effective materials to remove alkylphenols and alkylphenol ethoxylates from effluents at lab-scale, even at very low concentration. [START_REF] Tanghe | Adsorption of nonylphenol onto granular activated carbon[END_REF], studying adsorption of nonylphenol onto granular activated carbon, reported similar conclusion. The maximum adsorption capacity of granular activated carbon for nonylphenol was 100 mg/g (contact time of 4 d or 24 h depending on the carbon dosage used, 1 and 0.1 g/L, respectively). These authors also reported that the influence of temperature (4 °C and 28 °C) on performance was negligible and a full-scale carbon filter unit will be sufficient to remove environmentally relevant nonylphenol concentrations of 10 μg/L. Later, [START_REF] Tsyntsarski | Removal of detergents from water by adsorption on activated carbons obtained from various precursors[END_REF] demonstrated that the amount of carbon had no significant influence on performance. [START_REF] Yu | Adsorption of selected pharmaceuticals and an endocrine disrupting compound by granular activated carbon. 1. Adsorption capacity and kinetics[END_REF] evaluated the adsorption of nonylphenol on granular activated carbons, with a particular focus to adsorption mechanism. The authors demonstrated that film diffusion was the primary controlling mass transfer mechanism for very low concentrations of nonylphenol, and therefore must be accurately determined for good breakthrough predictions. However, film diffusion was difficult to predict with a correlation due to the complexity of carbon particle topography and system hydrodynamics. A discussion on adsorption mechanism and relationship between chemical and physical surface properties of carbons on alkylphenol removal can be found in [START_REF] Çeçen | Activated carbon for water and wastewater treatment. Integration of adsorption and biological treatment[END_REF].

Activated carbon technology is used at industrial scale not only for removing alkylphenols but also for other emerging substances [START_REF] Altmann | Direct comparison of ozonation and adsorption onto powdered activated carbon for micropollutant removal in advanced wastewater treatment[END_REF][START_REF] Nam | Adsorption characteristics of selected hydrophilic and hydrophobic micropollutants in water using activated carbon[END_REF][START_REF] Katsigiannis | Removal of emerging pollutants through granular activated carbon[END_REF][START_REF] Mailler | Removal of a wide range of emerging pollutants from wastewater treatment plant discharges by micro-grain activated carbon in fluidized bed as tertiary treatment at large pilot scale[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF][START_REF] Jeirani | Adsorption of emerging pollutants on activated carbon[END_REF][START_REF] Crini | Conventional and non-conventional adsorbents for wastewater treatment[END_REF][START_REF] Vatankhah | Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent[END_REF]). However, it presents several disadvantages. The adsorption efficiency depends on the type of carbon used, and the higher the quality, the greater the cost. Commercial activated carbons are also non-selective [START_REF] Dąbrowski | Adsorption of phenolic compounds by activated carbon -a critical review[END_REF][START_REF] Crini | Sorption processes and pollution[END_REF][START_REF] Rivera-Utrilla | Activated carbon modifications to enhance its water treatment applications. An overview[END_REF][START_REF] Vatankhah | Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent[END_REF]. Another problem is the rapid saturation of filters, and thus their regeneration. This regeneration step of saturated carbon is difficult and expensive, not straightforward, and results in loss of the adsorbent (the powdered form in particular poses a challenge from aqueous stream). For these reasons, their widespread use is restricted, in particular small and medium-size enterprises.

Over the past two decades, a new approach has been developed the development of composite adsorbents incorporating activated carbon. Another approach is to replace conventional activated carbons by other adsorbents, called non-conventional materials, such as, for example, cyclodextrin polymers, molecularly imprinted polymer and clays, which will be presented below. These adsorbents used to selectively remove alkylphenols have their own advantages and disadvantages [START_REF] Crini | Sorption processes and pollution[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF][START_REF] Crini | Conventional and non-conventional adsorbents for wastewater treatment[END_REF]. They are effective in treating emerging substances, but are basically at the laboratory stage despite undeniable progress.

Cyclodextrin Polymers for Sequestration of Alkylphenols

Cyclodextrins are natural oligosaccharides obtained by enzymatic degradation of starch. They have the ability to form inclusion complexes with a wide range of hydrophobic molecules. This property has, for example, been used by the pharmaceutical industry since the 1980s to complex active pharmaceutical ingredients. Cyclodextrins also find many applications in our daily lives, from cosmetics to food, textiles, agrochemicals, chromatography, catalysis, in the packaging industry and in the veterinary field. In recent years, cyclodextrin polymers have been proposed as innovative materials for their ability to selectively complex pollutants substances present in complex effluents, such as dyes, aromatic compounds, chlorophenols, pesticides and metals. It's a growing sector. These commercial polymers are also becoming very popular for the tracking and removal of trace emerging substances such as pharmaceuticals, personal care products, surfactants and other industrial products [START_REF] Morin-Crini | Environmental applications of water-insoluble β-cyclodextrinepichlorohydrin polymers[END_REF][START_REF] Cova | Cyclodextrin-based materials for removing micropollutants from wastewater[END_REF]Crini et al. 2018;[START_REF] Morin-Crini | Waterinsoluble β-cyclodextrin-epichlorohydrin polymers for removal of pollutants from aqueous solutions by sorption processes using batch studies: a review of inclusion mechanism[END_REF][START_REF] Fenyvesi | Applications of steroid drugs entrapped in cyclodextrins[END_REF][START_REF] Fenyvesi | Removal of hazardous micropollutants from treated wastewater using cyclodextrin bead polymer -a pilot demonstration case[END_REF][START_REF] Fernández | Complex systems that incorporate cyclodextrins to get materials for some specific applications[END_REF][START_REF] Sikder | Remediation of water pollution with native cyclodextrins and modified cyclodextrins: a comparative overview and perspectives[END_REF].

The hydrophobic cavity of cyclodextrin molecules allows the formation of hostguest inclusion complexes with suitable guest molecules through numerous interactions including van der Waals forces, hydrophobic interactions and hydrogen bonds (Fig. 4.3). Thus, this molecular encapsulation via cyclodextrin can be used to form a functional material for separating, anchoring and removing organic contaminants from harmful matrices (Morin- [START_REF] Morin-Crini | Environmental applications of water-insoluble β-cyclodextrinepichlorohydrin polymers[END_REF]Crini et al. 2018;[START_REF] Morin-Crini | Waterinsoluble β-cyclodextrin-epichlorohydrin polymers for removal of pollutants from aqueous solutions by sorption processes using batch studies: a review of inclusion mechanism[END_REF]. Incorporation of cyclodextrin into materials can be achieved by a facile chemical cross-linking reaction and among the materials, the most popular is an O-alkylated polymeric resin produced by reaction of cyclodextrin molecules with epichlorohydrin used as cross-linked [START_REF] Crini | Synthesis and applications of adsorbents containing cyclodextrins[END_REF][START_REF] Romo | Sorption of dibenzofuran derivatives from aqueous solutions by β-cyclodextrin polymers: an isosteric heat approach[END_REF][START_REF] Crini | Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment[END_REF][START_REF] García-Zubiri | Thermal stability of solid dispersions of naphthalene derivatives with β-cyclodextrin and β-cyclodextrin polymers[END_REF][START_REF] Mohamed | Evaluation of the accessible inclusion sites in copolymer materials containing beta-cyclodextrin[END_REF][START_REF] Morin-Crini | Environmental applications of water-insoluble β-cyclodextrinepichlorohydrin polymers[END_REF]. A commercial analog of cyclodextrin-epichlorohydrin polymer is Sephadex® using dextran instead of cyclodextrins (Fig. 4.4).

Cyclodextrin polymers are suitable materials for several reasons. Their one-step synthesis in water in simple, easy to set up in a lab, requires only mild reactions conditions (water-based chemistry, mild temperatures at atmospheric pressure), where the reagents involved are easy to find. Epichlorohydrin is not expensive and its mode of action is well understood. It is the most frequently used cross-linking agent in polysaccharide chemistry. Various types of materials can be obtained with physical textural, mechanical and chemical properties that can be varied giving different forms such as gels, powders, beads, nanoparticles, foams and sponges. The materials can be porous or non-porous with hydrophilic and hydrophobic properties. Their properties are strictly related to their 3D macromolecular structure. The most remarkable property of cyclodextrin polymers is their ability to generate both inclusion complexes (Fig. 4.5) and association complexes (cooperation between cyclodextrin cavities). In general, the performance in terms of pollutant removal can be explained not only by these two phenomena but also by the 3D network of polymer that allows the material to trap pollutants through additional interactions that complement complexation. This is why pollutants are more efficiently sequestered by cyclodextrin polymers than by native cyclodextrins, regardless of the complex structure of the pollutant. In addition, another advantage of these polymers is that, compared to commercial materials such as activated carbons and organic resins, cyclodextrin polymers are able to specifically interact with pollutants present as traces in complex mixtures. There regeneration is also easier and more environmentally friendly.

Cyclodextrins have long been studied in the field of separation science (mainly chromatography) and have received considerable attention over the last two decades for their performance in environmental remediation-based applications, particularly in wastewater treatment (Fourmentin et al. 2018;[START_REF] Barbosa | Chemical modifications of cyclodextrin and chitosan for biological and environmental applications: metals and organic pollutants adsorption and removal[END_REF][START_REF] Celebioglu | Water-insoluble hydrophilic electrospun fibrous mat of cyclodextrin-epichlorohydrin polymer as highly effective sorbent[END_REF][START_REF] Crini | Conventional and non-conventional adsorbents for wastewater treatment[END_REF][START_REF] Murcia-Salvador | Adsorption of direct blue 78 using chitosan and cyclodextrins as adsorbents[END_REF][START_REF] Pellicer | Adsorption properties of β-and hydroxypropyl-βcyclodextrins cross-linked with epichlorohydrin in aqueous solution. A sustainable recycling strategy in textile dyeing process[END_REF][START_REF] Qin | β-Cyclodextrin-crosslinked polymeric adsorbent for simultaneous removal and stepwise recovery of organic dyes and heavy metal ions: fabrication, performance and mechanism[END_REF][START_REF] Romita | Operational parameters affecting the atrazine removal from water by using cyclodextrin based polymers as efficient adsorbents for cleaner technologies[END_REF][START_REF] Xiao | Cross-linker chemistry determines the uptake potential of perfluorinated alkyl substances by beta-cyclodextrin polymers[END_REF][START_REF] Xu | Simple synthesis of a swellable porous β-cyclodextrin-based polymer in the aqueous phase for the rapid removal of organic micro-pollutants from water[END_REF][START_REF] Fenyvesi | Removal of hazardous micropollutants from treated wastewater using cyclodextrin bead polymer -a pilot demonstration case[END_REF]. Cyclodextrin polymers are used as sorbents in liquid-solid sorption processes to remove a fairly broad list of contaminants, ranging from benzene-and phenol-based substances to volatile organic compounds, dyes, pharmaceuticals, pesticides, and metals. Over the past decade, these polymers have been proposed to eliminate endocrine disruptors and other emerging pollutants such as non-steroidal anti-inflammatory drugs, estrogens, hormones, bisphenol A, and perfluorinated alkyl substances. These polymers may also interact with non-ionic and ionic surfactants [START_REF] Cserhati | Fast analysis of 4-tertoctylphenol, pentachlorophenol and 4-nonylphenol in river sediments by QuEChERS extraction procedure combined with GC-QqQ-MS/MS[END_REF][START_REF] Murai | Adsorption and recovery of nonionic surfactants by β-cyclodextrin polymer[END_REF][START_REF] Murai | Adsorption and recovery of ionic surfactants by β-cyclodextrin polymer[END_REF][START_REF] Murai | Removal of phenolic compounds from aqueous solution by beta-cyclodextrin polymer[END_REF] and detergents but studies on the removal of alkylphenols are rare [START_REF] Takeda | Separation of bisphenol A and three alkylphenols by micellar electrokinetic chromatography[END_REF][START_REF] Murai | Removal of phenolic compounds from aqueous solution by beta-cyclodextrin polymer[END_REF][START_REF] Bonenfant | UV-Vis and FTIR spectroscopic analyses of inclusion complexes of nonylphenol and nonylphenol ethoxylate with β-cyclodextrin[END_REF][START_REF] Bonenfant | Adsorption and recovery of nonylphenol ethoxylate on a crosslinked β-cyclodextrin-carboxymethylcellulose polymer[END_REF][START_REF] Bonenfant | Adsorption study of a commonly used antidepressant drug, fluoxetine hydrochloride, onto a crosslinked β-cyclodextrincarboxymethylcellulose polymer[END_REF][START_REF] Sancey | Décontamination des effluents de traitement de surface par oxydation/ bioadsorption sur cyclodextrine (in French)[END_REF][START_REF] Charles | Advanced oxidation (UV-ozone) and cyclodextrin sorption: effects of individual and combined action on the chemical abatement of organic pollutants in industrial effluents[END_REF][START_REF] Charles | Pollutant removal from industrial discharge water using individual and combined effects of adsorption and ion-exchange processes: chemical abatement[END_REF]. [START_REF] Murai | Adsorption and recovery of nonionic surfactants by β-cyclodextrin polymer[END_REF][START_REF] Murai | Adsorption and recovery of ionic surfactants by β-cyclodextrin polymer[END_REF] were the first to suggest that cyclodextrin polymers can retain different alkylphenols by forming inclusion complexes with cyclodextrin molecules. The performances were high: 1 g of material was able to adsorb 85% of alkylphenol ethoxylate from a 150 mL solution containing 200 ppm of nonionic surfactant. However, kinetics were relatively slow. The authors demonstrated that the materials could be used in batch or column adsorption experiments with surprisingly similar performances. Another interesting feature was the fact that the sorbents proposed can be easily regenerated. At the end of the 2000s, Hausler's group also showed the efficiency of cyclodextrin polymers for the removal of alkylphenol monoethoxylates [START_REF] Bonenfant | UV-Vis and FTIR spectroscopic analyses of inclusion complexes of nonylphenol and nonylphenol ethoxylate with β-cyclodextrin[END_REF][START_REF] Bonenfant | Adsorption and recovery of nonylphenol ethoxylate on a crosslinked β-cyclodextrin-carboxymethylcellulose polymer[END_REF][START_REF] Bonenfant | Adsorption study of a commonly used antidepressant drug, fluoxetine hydrochloride, onto a crosslinked β-cyclodextrincarboxymethylcellulose polymer[END_REF]. The experiments were performed using synthetic solutions containing 500 mg of material and aqueous alkylphenol mono-and diethoxylate solutions at concentrations of 12-82 mg/L. The abatement performance of the material was between 1.1 and 6.8 mg of pollutant adsorbed whatever the initial concentration. The data indicated a relationship between the chemical structure of the organic pollutant and the performance of the materials. Later, Crini's group also demonstrated that the adsorptive uptake of such materials depended on their textural properties and surface chemistry [START_REF] Sancey | Heavy metal removal from industrial effluents by sorption on cross-linked starch: chemical study and impact on water toxicity[END_REF][START_REF] Sancey | Décontamination des effluents de traitement de surface par oxydation/ bioadsorption sur cyclodextrine (in French)[END_REF][START_REF] Charles | Advanced oxidation (UV-ozone) and cyclodextrin sorption: effects of individual and combined action on the chemical abatement of organic pollutants in industrial effluents[END_REF][START_REF] Charles | Pollutant removal from industrial discharge water using individual and combined effects of adsorption and ion-exchange processes: chemical abatement[END_REF]. Their results also demonstrated that cyclodextrin polymers presented a facility of regeneration, and after this treatment, the performance remained unchanged showing both the chemical stability of the polymers and the reproducibility of the values.

Figure 4.6 compares the performance of five materials on the removal of several alkylphenols, (see Figs. 4.1 and 4.2 for their structure), present in synthetic solution at a concentration of 100 μg/L. The alkylphenols are a mixture of nonylphenol (NP, CAS number 25154-52-3), a mixture of 4-nonylphenol (4-NP, CAS number 84852-15-3), the linear para-nonylphenol (4-n-NP, CAS number 104-40-5), the linear para-octylphenol (4-n-OP, CAS number 1806-26-4), and the para-octylphenol (4-tert-OP, CAS number 140-66-9). It clearly shows that the cyclodextrin polymer and commercial activated carbon have the best performance relative to the other materials, regardless the contaminant studied. As expected, conventional carbon had the highest levels of alkylphenol removal (close to 100%). This result also indicates that adsorption onto carbon is non-selective. For cyclodextrin polymer, the order of sorption is as follows: 4-tert-octylphenol > nonylphenol >4-n-nonylphenol ~4-n-octylphenol >4-nonylphenol. If the values obtained for 4-tert-octylphenol and 4-nonylphenol are compared, an important decrease is observed, suggesting that the difference in the chemical structure between these two substances may explain the different obtained values. On the contrary, sucrose-and starch-based polymers were not able to remove alkylphenols (<10% and <20% respectively), suggesting that for cyclodextrin polymer, the main mechanism for adsorption of alkylphenols in these materials was inclusion within the cyclodextrin cavities. It is interesting to note that, although it does not have the type of cavity that participates in inclusion complexes, cross-linked maltodextrin has an adsorption capacity towards alkylphenols (the performances obtained are nevertheless inferior to those of cross-linked cyclodextrins). This result shows that the macromolecular structure of the material must also be taken into account to explain the adsorption mechanism. Figure 4.7 reports the effect of the initial alkylphenol concentration on the performance of a cyclodextrin polymer to remove five alkylphenols from monocontaminated solution. At any concentration, the same order of abatement was obtained for all alkylphenols studied. The affinity was independent of alkylphenol concentration between 25 and 100 μg/L. For a concentration below 25 μg/L, all the alkylphenol present in each solution is adsorbed (values below the quantification limit). For the concentration range studied (25-100 μg/L), the 4-tert-octylphenol substance showed the highest affinity. For other compounds, when the alkylphenol concentration was increased, sorption efficiency decreased, due to the saturation of the site on the material and/or steric effects. For example, for 4-nonylphenol, when the initial concentration was increased from 25 to 100 μg/L, the removal decreased from 97 to 69%.

Figure 4.8 compares the removal of five alkylphenols in a mixture at three concentrations by a cyclodextrin polymer (fixed conditions: adsorbent dose, contact time, T 25 °C). These results show that the performance obtained changed for each alkylphenol alone or in the presence of the others, suggesting the presence of competition effects between contaminants. Differences in the degree of sorption can be attributed to the chemical structure of each alkylphenol (Fig. 4.2). Indeed, it is known that the size of each molecule can determine its accessibility to the cyclodextrin-based network. Thus, steric effects can also be advanced to explain the differences of adsorption observed for cyclodextrin polymer between alkylphenols when they were in a mixture. Figure 4.9 shows the effect of the presence of NaCl on the performance of cyclodextrin polymer for five alkylphenols. Their removal was significantly decreased in the presence of NaCl for all substances. Probably, NaCl maximizes electrical charge on the surface of the material by masking of adsorption sites, thus decreasing attraction interactions that negatively affect complexation. With the exception of a few very recent works [START_REF] Charles | Advanced oxidation (UV-ozone) and cyclodextrin sorption: effects of individual and combined action on the chemical abatement of organic pollutants in industrial effluents[END_REF][START_REF] Charles | Pollutant removal from industrial discharge water using individual and combined effects of adsorption and ion-exchange processes: chemical abatement[END_REF], studies of real concrete cases are rare. Table 4.3 shows the values obtained before and after treatment for three industrial effluents. Analytical monitoring of these effluents showed that nine alkylphenols were found at least once. Of these, nonylphenol, nonylphenol diethoxylate, 4-n-octylphenol, 4-n-octylphenol and 4-tert-octylphenol systematically occurred at detectable concentrations. Others alkylphenols and alkylphenol polyethoxylates were below the limit of quantification. The data shows that the real effluents before treatment contained a variable load of alkylphenols not only in quality (number of substances detected) but also in quantity (measured concentrations). After treatment by sorption onto a cyclodextrin polymer, high levels of alkylphenol removal are achieved using cyclodextrin materials (Table 4.3).

Numerous studies demonstrated that cyclodextrin polymers are a promising alternative in the treatment of wastewater containing a cocktail of emerging trace substances, mostly at lab-scale. Recently, a company has developed new ecofriendly cyclodextrin polymers (Dexsorb® adsorbents of Cyclopure company; Cyclopure 2020), which can quickly and safely remove from water hundreds of emerging substances. These commercial adsorbents are produced in varying formats, allowing for use in analytical, household and municipal water treatment applications. Industrialists will now have to be to convinced to use cyclodextrin polymers in their municipal wastewater treatment plants.

Molecularly Imprinted Polymer for Selective Removal of Alkylphenols

Molecularly imprinted polymers are commercial synthetic materials in various forms to suit the target desired application, obtained by polymerizing functional monomers and cross-linked them in the presence of a template [START_REF] Alexander | Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003[END_REF]. When the template is then removed, it leaves a cavity capable of recognizing and selectively binding to the imprinted compound. These new class of materials combine the robustness of cross-linked polymers with the attractive properties of natural receptors, mimicking molecular recognition by biological receptors [START_REF] Huang | Application of molecularly imprinted polymers in wastewater treatment: a review[END_REF][START_REF] Cantarella | Molecularly imprinted polymer for selective adsorption of diclofenac from contaminated water[END_REF].

Molecularly imprinted polymers are used as separation and extraction materials and as sensors in many applications, including solid-phase extraction, chromatography, analytical chemistry, food separation, medical applications, drug delivery, protein recognition and purification, biomarkers and molecule detection (BelBruno 2019). Many recent studies have reported novel results on the use of molecularly imprinted polymers as selective adsorbents for the removal of pharmaceuticals, personal care products and pesticides [START_REF] Murray | Application of molecularly imprinted and non-imprinted polymers for removal of emerging contaminants in water and wastewater treatment: a review[END_REF][START_REF] Alvarez-Lorenzo | Handbook of molecularly imprinted polymers[END_REF][START_REF] Chen | Molecularly imprinted hollow spheres for the solid phase extraction of estrogens[END_REF][START_REF] Chen | Molecular imprinting: perspectives and applications[END_REF][START_REF] Huang | Application of molecularly imprinted polymers in wastewater treatment: a review[END_REF][START_REF] Madikizela | Applications of molecularly imprinted polymers for solid-phase extraction of non-steroidal anti-inflammatory drugs and analgesics from environmental waters and biological samples[END_REF][START_REF] Cantarella | Functional nanomaterials for water purification[END_REF][START_REF] Cantarella | Molecularly imprinted polymer for selective adsorption of diclofenac from contaminated water[END_REF]. For water applications, the main advantages of these polymers are their ease of preparation, available in a wide variety of shapes and sizes, their relatively low cost, their physical and chemical stability, and their effectiveness in removing chemicals and pathogens. Another important feature is that molecularly imprinted polymers are easily regenerated and reusable several times.

Molecularly imprinted polymers could also be a promising adsorbent for the removal of alkylphenols [START_REF] Murray | Application of molecularly imprinted and non-imprinted polymers for removal of emerging contaminants in water and wastewater treatment: a review[END_REF][START_REF] Alvarez-Lorenzo | Handbook of molecularly imprinted polymers[END_REF][START_REF] Matějíček | The use of molecularly imprinted polymers for the multicomponent determination of endocrine-disrupting compounds in water and sediment[END_REF][START_REF] Gryshchenko | Development of molecularly imprinted polymer in porous film format for binding of phenol and alkylphenols from water[END_REF][START_REF] Huang | Application of molecularly imprinted polymers in wastewater treatment: a review[END_REF][START_REF] Xie | Novel magnetic multitemplates molecularly imprinted polymer for selective and rapid removal and detection of alkylphenols in water[END_REF]. For example, [START_REF] Xie | Novel magnetic multitemplates molecularly imprinted polymer for selective and rapid removal and detection of alkylphenols in water[END_REF] reported that molecularly imprinted polymers had remarkable adsorption capacity, kinetics and reusability compared to other adsorbents. The maximum adsorption capacities of the MIP for 4-tert-octylphenol and 4-nonylphenol were 35.97 and 61.73 mg/g, respectively, which were significantly higher than those of the non-molecularly imprinted polymer due to the imprinting effect and other adsorbents. Alkylphenol adsorption reached equilibrium within 30 min, and could be reused five times. The polymers also showed high selectivity towards alkylphenols and real water samples gave satisfactory results. [START_REF] Gryshchenko | Development of molecularly imprinted polymer in porous film format for binding of phenol and alkylphenols from water[END_REF] also reported that molecularly imprinted polymers could be a promising adsorbent for separation and analysis of alkylphenols.

Based on data from the literature, there is no doubt that molecularly imprinted polymers have high adsorption capacities. However, studies on these materials in the field of water treatment are at the laboratory stage and pilot studies need to be conducted.

Adsorption of Alkylphenols onto Clays

Adsorbents such as clay minerals and modified clays are efficient for the removal of contaminants from wastewater and drinking water sources, even at trace levels. These materials have high specific surface area, porous structures and defined particles sizes, which facilitates physical and chemical interactions with dissolved species. In addition, natural clays are abundant and low-cost resource, and the technological process is simple. Numerous studies have been published on the removal of dyes, metals and organics (phenol, chlorophenols) present in industrial wastewaters, with high levels of performance (the maximum efficiency can reach 100%). The mechanisms such as ion-exchange, surface complexation and direct bonding of contaminants to the clay surface are also well-known [START_REF] Espantaleon | Use of activated clays in the removal of dyes and surfactants from tannery waste waters[END_REF][START_REF] Nagasaki | Sorption of nonylphenol on Na-montmorillonite[END_REF][START_REF] Priac | Alkylphenol and alkylphenol polyethoxylates in water and wastewater: a review of options for their elimination[END_REF]. A survey of data literature shows that clays can also be used as efficient adsorbents for the removal of alkylphenol using clays. However, in the field of water data are rather rare, whereas studies on alkylphenol-clay interactions in soils or alkylphenol-sludge interactions are more numerous.

To reduce the pollution of effluents produced in tanning, [START_REF] Espantaleon | Use of activated clays in the removal of dyes and surfactants from tannery waste waters[END_REF] proposed a simple, selective and economical alternative to conventional physical-chemical treatments based on modified clays using batch experiments. These materials, obtained using the activation of natural bentonite by a 0.5 M H 2 SO 4 solution, were used as effective adsorbent for alkylphenol ethoxylates removal. [START_REF] Nagasaki | Sorption of nonylphenol on Na-montmorillonite[END_REF] also proposed a simple method of oriented-adsorption onto clays to reduce the contamination of solutions by nonylphenol. The authors studied the adsorption of nonylphenol on Na-montmorillonite. The results of a series of batch experiments were compared to those obtained using α-SiO 2 , α-Al 2 O 3 and gibbsite. It was found that nonylphenol adsorption on Na-montmorillonite reached the equilibrium state within 24 h, and that the interlayer width of Na-montmorillonite did not change before and after the adsorption. These data suggest that nonylphenol was adsorbed on the outer surface of Na-montmorillonite. The amount of nonylphenol adsorbed on the surface of octahedral sheets of Na-montmorillonite was found to be identical to that adsorbed to gibbsite. On the other hand, adsorption on α-Al 2 O 3 was smaller, and that on α-SiO 2 was very low. Adsorption amount was found to increase monotonously with pH. It was noted that nonylphenol was adsorbed on the broken edges of the octahedral alumina sheets of Na-montmorillonite.

Another interesting topic in the literature is the study of interactions of alkylphenols and soils. Alkylphenols and alkylphenol ethoxylates occurrence in soil is related to anthropogenic activities such as sewage sludge application, land filling and accidental spills. As already mentioned, tons of nonionic surfactants are produced in Europe every year. In municipal wastewater treatment plants, alkylphenol ethoxylates are partly degraded to alkylphenols by shortening the hydrophilic chain of the ethoxylates. These compounds are then degraded in anaerobically stabilized sewage sludge to yield fully diethoxylated 4-nonylphenol, a more lipophilic and toxic substance that resists to further microbial degradation.

Alkylphenols can be found not only in aqueous compartments (surface water, groundwater, sediment) and sludge, but also in soils and even in the air [START_REF] Kovarova | Alkylphenol ethoxylates and alkylphenols -update information on occurrence, fate and toxicity in aquatic environment[END_REF][START_REF] Salomon | Nonylphenol and its ethoxylate in water environment[END_REF]. They have also detected in drinking water and milk. Indeed, these substances can end up in the environment, for example when sewage sludge is spread in agriculture (this activity is regulated in Europe, although there are no limit values set for sludge). The presence of substances in sewage sludge is a growing concern for farmers, and for society in general, because alkylphenols, such as nonylphenol, are considered to be endocrine disruptors, affecting the reproductive capacity of animals and humans [START_REF] Naim | Tritium radioactivity in the aquatic environment over Alexandria region, Egypt[END_REF][START_REF] Claisse | Review of "emerging" organic contaminants in biosolids and assessment of international research priorities for the agricultural use of biosolids[END_REF][START_REF] Cocchieri | Total tin and organotin in seawater from the gulf of Naples, Italy[END_REF][START_REF] Smith | Adsorptive selectivity of organic-cation-modified bentonite for non-ionic organic contaminants[END_REF][START_REF] Ginsberg | Environmental oestrogens[END_REF]). From a scientific point of view, adsorption and desorption of alkylphenols and alkylphenol ethoxylates in sewage sludge and soils is a hot topic. For example, an interesting challenge is to understand the uptake of alkylphenols by plants from sludgeamended soils because this depends on its bioavailability, which is determined by sorption behavior. In this context, it is important to understand how alkylphenol compounds are bound by the soil components and how they migrate. As most of them have a very low solubility, it may be interesting to consider that their transport in groundwater as well as their binding to soil components could be enhanced by their parent molecules, i.e. the nonionic surfactants, from which they are derived. A detailed study of the coadsorption of alkylphenol compounds, such as paramethylphenol, parapropylphenol and para-nonylphenol, with nonionic surfactants has been published by Barhoumi's group (Barhoumi et al. 2003a(Barhoumi et al. , b, 2006;;[START_REF] Barhoumi | Adsorption of alkylphenols onto green clay surface in the presence of non-ionic surfactant[END_REF].

Small hydrophobic molecules such as phenol can be solubilized by surfactant micelles. These provide an environment in which these compounds can find a more stable state than in aqueous solution. The hydrocarbon core of the micelles gives them the ability to solubilize hydrophobic compounds. As a result, numerous studies have shown that surfactant micelles significantly improve the apparent solubility of hydrophobic organic compounds in water [START_REF] Abdul | Selection of surfactants for the removal of petroleum-products from shallow sandy aquifers[END_REF][START_REF] Fountain | Cyclodextrin applications in medicine, food[END_REF][START_REF] Pennell | Surfactant-enhanced solubilization of residual dodecane in soil columns. 1. Experimental investigation[END_REF][START_REF] Pennell | Surfactant enhanced remediation of soil columns contaminated by residual tetrachloroethylene[END_REF][START_REF] Shiau | Solubilization and microemulsification of chlorinated solvents using direct food additive (edible) surfactants[END_REF]. Hydrophobic molecules may also interact with adsorbed surfactants. This is due to the structure of surfactants adsorbed phases. The adsorption mechanism of surfactants onto minerals is now well known. At low equilibrium concentrations, surfactants may be adsorbed as isolated molecules. Surfactant surface aggregates can solubilize hydrophobic molecules as do bulk micelles. The consequence may be an apparent increase in the adsorbed amount of the solute when a surfactant molecule is present in the system. Two situations may be encountered. Firstly, the solute molecule is not adsorbed by the solid surface when alone, but is adsorbed when a surfactant molecule is adsorbed: this process is often called "adsolubilization". Secondly, the solute is adsorbed by the solid surface when it is alone and its surface concentration is increased in the presence of a surfactant: this is a coadsorption process.

The adsorption of alkylphenols from aqueous solution onto kaolinite was first studied and compared to the case of phenol (molecular weight MW 94.1 g/mol; solubility 85 g/L at 25 °C). para-Methylphenol (MW 108.1 g/mol; solubility 19 g/L at 25 °C), para-propylphenol (MW 136.1 g/mol; solubility 3 g/L) and paranonylphenol (MW 220.3 g/mol; solubility 0.005 g/L) were chosen as test solutes (Barhoumi et al. 2003a(Barhoumi et al. , b, 2006)). Adsorption of alkylphenol was studied in the presence of an alkylphenol polyethoxy nonionic surfactant, and isotherms were determined by the solution depletion method. As the alkylphenol and the surfactant molecules had very similar UV spectra, a specific method was used to determine the phenol function content of the solutions.

Phenol, like alcohol, is only weakly adsorbed by oxide surfaces, as water is preferentially adsorbed. The adsorption isotherms indicate the amount of mole of alkylphenol per unit area as a function of its equilibrium solution concentration. Barhoumi et al. (2003a) previously reported that phenol had only a low affinity for this type of surface. Its plateau surface concentration was 0.06 μmol/m 2 and the adsorption isotherm is L-shaped (Langmuir type), suggesting that only a limited number of surface sites are adsorption sites for phenol molecules and that no lateral interaction effects are visible between adsorbed molecules. The behavior of alkylphenols was completely different [START_REF] Barhoumi | Adsorption of alkylphenols onto green clay surface in the presence of non-ionic surfactant[END_REF]: the curves showed S-shaped adsorption isotherms that were very similar to the adsorption isotherms of surfactants. Each of these adsorption isotherms had a clear plateau which corresponded to a high surface concentration compared to that of phenol. This behavior may indicate an aggregation of alkylphenols at the interface, as do surfactants. These molecules are not considered to be surfactants due to an unfavorable size ratio of the hydrophilic and hydrophobic parts of the molecule, alkylphenols are not subject to micelle formation. Nevertheless, they are so hydrophobic that it is easy to imagine that once a few of them are attached to the surface, they can become anchor points for the others. Their structure is close to that of non-ionic surfactants, which may explain why they can have similar properties at the interface [START_REF] Barhoumi | Adsorption of alkylphenols onto green clay surface in the presence of non-ionic surfactant[END_REF].

The adsorption isotherms of paramethylphenol in the presence of Triton™ X-100 (an octylphenol ethoxylate with 9.5 ethylene oxide units) were also carried out together with the evolution of the surface concentration of Triton™ X-100. The critical micelle concentration of Triton™ X-100 is 0.27 mmol/L. Isotherms were also determined by solution depletion methods. Other results showed that the longer the alkyl chain, the lower was the adsolubilization part in the adsorption process. Since the surfactant is not displaced by the adsorption of alkylphenols, it is possible that the adsorption sites of the alkylphenol molecules (when alone) are different from the adsorption sites of the surfactant. In this case, the adsorption of surfactant and solute is therefore not competitive. In summary, alkylphenols can be adsorbed by kaolinite with a mechanism close to that of surfactants. If a non-ionic surfactant is added to the medium, the adsorbent properties are modified according to the length of the alkyl chain. The longer the length of the alkyl chain of alkylphenol derivatives, the smaller the influence of the surface aggregates Triton™ X-100 on their adsorption behavior. The total capacity is increased in all cases, but in the range of low solute concentrations, the initial slope is less and less modified as the length of the chain increases. This unexpected behavior, depending on the relative hydrophobicity of the molecules, may be due in part to the adsorbent properties of alkylphenols that are capable of aggregating alone at the kaolinite/water interface and in part to the limited swelling capacity of the surface micelles of Triton™ X-100.

Remediation of Alkylphenols Using

Biotechnological Processes

Alkylphenol Removal Using Microalgae

Algae-based technologies are alternative options for treating wastewater and generating useful products at low cost and high efficiency [START_REF] Biris-Dorhoi | Applications of microalgae in wastewater treatments: a review[END_REF][START_REF] Hwang | Use of microalgae for advanced wastewater treatment and sustainable bioenergy generation[END_REF][START_REF] Molazadeh | The use of microalgae for coupling wastewater treatment with CO 2 biofixation[END_REF][START_REF] Wollmann | Microalgae wastewater treatment: biological and technological approaches[END_REF]. Indeed, the cultivation of microalgae offers a chemically efficient step for wastewater treatment plants, combined with the production of potentially valuable biomass. For water treatment applications, microalgae have the following high adsorption capacity, high surface area/volume ratio, wide distribution range, rapid metabolism, low cost, and abundant availability. Algae-based technologies can be easily integrated into a wastewater treatment plant as secondary or final treatment. Data from the literature show that algal-based treatments appear to work well compared to chemical processes, which are generally too expensive to be implemented in most places and may result in secondary pollution. In addition, the algal biomass produced during treatment can be used for methane production, composting, production of fuels or fine chemicals, and as animal feed or in aquaculture.

Algae-based technologies can treat human sewage, livestock waste, agroindustrial waste, pig farm effluents, agricultural waste and wastewater from food processing. Microalgae have the potential to effectively remove not only nutrients (they use nitrogen and phosphorus for growth) and coliform bacteria from wastewater and reduce conventional water parameters such as chemical and biochemical oxygen demand [START_REF] Biris-Dorhoi | Applications of microalgae in wastewater treatments: a review[END_REF][START_REF] Wollmann | Microalgae wastewater treatment: biological and technological approaches[END_REF]), but also pollutants (metals) and emerging substances [START_REF] Abdel-Raouf | Microalgae and wastewater treatment[END_REF][START_REF] Biris-Dorhoi | Applications of microalgae in wastewater treatments: a review[END_REF][START_REF] Delrue | The environmental biorefinery: using microalgae to remediate wastewater, a win-win paradigm[END_REF][START_REF] Maza-Márquez | Chapter 8: Microalgae-bacteria consortia for the removal of phenolic compounds from industrial wastewaters[END_REF][START_REF] Gupta | Application of microalgae in wastewater. Domestic and industrial wastewater treatment[END_REF]. Indeed, they have been known for many years for their ability to degrade/eliminate toxic organic substances such as chlorophenols, polycyclic aromatic compounds, hormones (progesterone, norgestrel), antibiotics (tetracycline), triclosan and pesticides (α-endosulfan) [START_REF] Mara | Artificial freshwater environment: waste stabilization ponds[END_REF][START_REF] De La Noüe | The potential of microalgal biotechnology. A review of production and uses of microalgae[END_REF][START_REF] Redalje | Algae as ideal waste removers: biochemical pathways[END_REF][START_REF] Muñoz | Algal-bacterial processes for the treatment of hazardous contaminants: a review[END_REF]. They biodegrade or biotransform pollutants through metabolic action, and mechanisms include accumulation and degradation, which includes adsorption, transformation and mineralization. Microalgae also produce oxygen and have a disinfectant effect due to the increase in pH during photosynthesis [START_REF] Mara | Artificial freshwater environment: waste stabilization ponds[END_REF].

The great advantage of this biotechnology is that most of the algal species with proven efficacy are readily available, especially in countries that lack infrastructure for wastewater treatment. As photosynthesis is a key process for the cultivation of microalgae, these systems are ideal for regions with high temperatures and exposure to sunlight. In addition, when combined with conventional activated sludge systems, algal-bacterial symbiosis can reduce the electrical energy requirements for aeration [START_REF] Redalje | Algae as ideal waste removers: biochemical pathways[END_REF]). For all these reasons, these biological processes develop [START_REF] Biris-Dorhoi | Applications of microalgae in wastewater treatments: a review[END_REF][START_REF] Hwang | Use of microalgae for advanced wastewater treatment and sustainable bioenergy generation[END_REF][START_REF] Molazadeh | The use of microalgae for coupling wastewater treatment with CO 2 biofixation[END_REF][START_REF] Wollmann | Microalgae wastewater treatment: biological and technological approaches[END_REF].

Recent studies have also been reported the removal, biosorption and biodegradation of alkylphenols by microalgae [START_REF] Zhou | Cellular responses and bioremoval of nonylphenol and octylphenol in the freshwater green microalga Scenedesmus obliquus[END_REF][START_REF] Zhou | Simultaneous removal of inorganic and organic compounds in wastewater by freshwater green microalgae[END_REF][START_REF] Delrue | The environmental biorefinery: using microalgae to remediate wastewater, a win-win paradigm[END_REF][START_REF] He | Removal and biodegradation of nonylphenol by four freshwater microalgae[END_REF][START_REF] He | Phytotoxicity, bioaccumulation, and degradation of nonylphenol in different microalgal species without bacterial influences[END_REF][START_REF] Maza-Márquez | Chapter 8: Microalgae-bacteria consortia for the removal of phenolic compounds from industrial wastewaters[END_REF][START_REF] Gupta | Application of microalgae in wastewater. Domestic and industrial wastewater treatment[END_REF][START_REF] Wang | Biosorption and biodegradation of the environmental hormone nonylphenol by four marine microalgae[END_REF]. For example, [START_REF] Zhou | Cellular responses and bioremoval of nonylphenol and octylphenol in the freshwater green microalga Scenedesmus obliquus[END_REF][START_REF] Zhou | Simultaneous removal of inorganic and organic compounds in wastewater by freshwater green microalgae[END_REF] studied the removal of nonylphenol and octylphenol by the freshwater green microalga Scenedesmus obliquus in cultures exposed to different concentrations of alkylphenols for 5 days. At concentrations below 1 mg/L, the parameters growth, fluorescence transient, photosynthetic pigments and cell ultrastructure of Scenedesmus obliquus are not affected. This green microalga is commonly found in most types of freshwater, and plays an important part in the functioning of aquatic ecosystem. After 5 days of culturing, >89% nitrophenol and >58 octylphenol were eliminated by Scenedesmus obliquus. The dissolved concentrations for alkylphenols in the medium decreased rapidly: within one day, nonylphenol and octylphenol were rapidly eliminated with efficiencies of 70.9-90.4% for nonylphenol and 37.8-82.2% for octylphenol, depending on the initial concentration. The authors also showed that algae biomass yield decreased with increasing concentrations of nonylphenol and octylphenol. Algal growth was significantly inhibited at 4 mg/L for both compounds. The removal of alkylphenols was due to algal degradation and was primarily attributed to the process of cell biotransformation of the algae rather than simple adsorption and accumulation in the cells. Similar findings were previously reported by [START_REF] Gao | Removal and biodegradation of nonylphenol by different Chlorella species[END_REF] and [START_REF] Wang | Effects of nonylphenol on the growth and microcystin production of Microcystis strains[END_REF] for other algal species, Chlorella fusca and Microcystis aeruginosa, respectively. [START_REF] Zhou | Cellular responses and bioremoval of nonylphenol and octylphenol in the freshwater green microalga Scenedesmus obliquus[END_REF] concluded that technology based on the use of Scenedesmus obliquus was a potential approach for the removal of multicontaminants, including alkylphenols, in addition to nutrients and metals. Further examples can be found in the review published by [START_REF] Wang | Biosorption and biodegradation of the environmental hormone nonylphenol by four marine microalgae[END_REF].

The use of microalgae for wastewater treatment and the use of the resulting biomass for energy production is a two-pronged approach. Algae-based processes are already used on an industrial scale to treat so-called conventional pollution and there is no doubt that these green processes will continue to develop. However, the effect of these treatments on the monitoring of emerging substances such as alkylphenols is not yet systematically realized. There is also a need for research into degradation mechanisms.

Constructed Wetlands for the Removal of Alkylphenols

Constructed wetlands in combination with the use of plants are capable of removing conventional contaminants and emerging substances due to the interaction between plants and microorganisms (Garcia- Rodríguez et al. 2014;[START_REF] Gorito | A review on the application of constructed wetlands for the removal of priority substances and contaminants of emerging concern listed in recently launched EU legislation[END_REF][START_REF] Herrera-Melian | Study on the removal of hormones from domestic wastewaters with lab-scale constructed wetlands with different substrates and flow directions[END_REF][START_REF] Osei | Pollutant removal and growth dynamics of macrophyte species for faecal sludge treatment with constructed wetland technology[END_REF][START_REF] Dan | Accelerated biodegradation of p-tertbutylphenol in the Phragmites australis rhizosphere by phenolic root exudates[END_REF][START_REF] Kaur | Chapter 5: Constructed wetlands for the removal of organic micro-pollutants[END_REF]. In many countries of the world, they are considered to be an effective alternative to conventional biological treatments for municipal wastewater treatment to treat suspended solids, chemical oxygen demand, biological oxygen demand, nutrients (nitrogen, phosphate) and metals, which is why they have developed strongly [START_REF] Gorito | A review on the application of constructed wetlands for the removal of priority substances and contaminants of emerging concern listed in recently launched EU legislation[END_REF][START_REF] Schultze-Nobre | Removal of dimethylphenols and ammonium in laboratory-scale horizontal subsurface flow constructed wetlands[END_REF]. Constructed wetland technology is also being applied on a large scale for the treatment of industrial effluent from olive mills, wineries, coffee processing, and the pulp and paper industry [START_REF] Schultze-Nobre | Removal of dimethylphenols and ammonium in laboratory-scale horizontal subsurface flow constructed wetlands[END_REF]. They may also be considered for the treatment of agricultural runoff, animal wastewater, leachate, sludge and mine drainage. The advantages cited are simplicity, low operation/maintenance costs and environmental friendliness. Constructed wetland technology is a complex system containing water, solids (substrate, soil, plants) and microorganisms. Their design (wetland configuration, soil/ substrate matrix, plant species, hybrid systems, etc.) and operational factors (operating mode, hydraulic residence time, etc.) affect its performance. In this system, physical, chemical and biological processes may occur simultaneously, such as volatilization, adsorption, sedimentation, photodegradation, plant uptake and microbial degradation. The occurrence of these processes depends on various factors such as the physical and chemical characteristics of pollutants (hydrophobicity, vapor pressure, pKa, etc.), the properties of soil/substrate (e.g. important for the growth of plants and microorganisms), the conditions used (pH, temperature, ionic strength, oxygen, etc.), the seasonal variation, etc. A challenge for constructed wetland technology is the question of the presence of so-called emerging substances such as alkylphenols and their polyethoxylated derivatives. The increasing occurrence of organic pollutants in wastewater poses indeed a new challenge [START_REF] Kaur | Chapter 5: Constructed wetlands for the removal of organic micro-pollutants[END_REF].

A great deal of research has been carried out on this topic, showing promising results for the removal of emerging substances. It is demonstrated that the establishment of vegetation-based wastewater treatment systems, such as wetlands, is a potential approach to address contaminants of emerging concern. The presence of vegetation such as Phragmites australis in constructed wetlands can improve contaminant removal. The effect of plants is related to the release of root exudates, which may enhance the biodegradation of contaminants by recruiting specific microorganisms. In addition, vegetation makes the process more resistant to hydraulic changes. Several authors have also pointed out that some root exudates are linked to improved contaminant removal in planted constructed wetlands. It is already known that in terrestrial ecosystems, plant root exudates play a crucial role in the underground ecosystem. Plant roots create hotspots of biological activity in the soil by interacting with a diverse community of microorganisms, invertebrates and nearby plants. However, there is a lack of knowledge regarding the removal percentage attributable to plants and how plants affect this removal improvement.

Constructed wetlands have been investigated for the elimination/degradation of organic pollutants. Phenolic root exudates released from plants are potentially effective for the degradation of pharmaceuticals (de la Paz et al. 2019) and aromatic compounds such as dimethylphenols (Schultze-Nobre et al. 2017) and alkylphenols [START_REF] Hoang | Accelerated degradation of a variety of aromatic compounds by Spirodela polyrrhiza-bacterial associations and contribution of root exudates released from S. polyrrhiza[END_REF][START_REF] Dan | Accelerated biodegradation of p-tertbutylphenol in the Phragmites australis rhizosphere by phenolic root exudates[END_REF]. [START_REF] Schultze-Nobre | Removal of dimethylphenols and ammonium in laboratory-scale horizontal subsurface flow constructed wetlands[END_REF] studied the removal of dimethylphenols and ammonium in laboratory-scale horizontal subsurface flow constructed wetlands planted with Juncus effusus. Removal efficiencies of dimethylphenol was dependent on the inflow loading of the contaminant and was higher in the planted systems. Both planted systems yielded 99% removal efficiency up to loads of 240 mg/d, compared to only 73% for the unplanted constructed wetland. Highly efficient dimethylphenol removal was determined for inflow loads up to 240 mg/d (40 mg/L), whereas loads of 600 mg/d (100 mg/L) resulted in a decrease in treatment efficiency. Removal efficiency was also found to be higher in planted systems, as compared to unplanted wetlands, although the presence of a gravel bed, as well as the density of the above-ground plant biomass, did not significantly influence the efficiency of dimethylphenol removal between the two planted constructed wetlands. Higher amounts of surplus organic carbon were detected in the hydroponic constructed wetland, suggesting incomplete dimethylphenol transformation and/or a more intensive release of organic substances from the plant roots as a response to possible toxic stress. Both aerobic and anaerobic processes should be responsible for carbon and nitrogen transformation and methane generation, which is of greatest importance in the inflow sections of both planted constructed wetlands. Ammonium removal was found to be highly efficient in the planted constructed wetland and insufficient in the unplanted counter-part. The authors concluded that horizontal subsurface flow constructed wetlands planted with Juncus effusus were a promising alternative system for the treatment of effluents contaminated with dimethylphenol isomers.

p-tert-Butylphenol is an important industrial chemical that is widely used in the production of phenolic resins and surfactant. However, it is recognized as an important hazardous contaminant because of its acute and chronic toxicities and estrogenic activity. This emerging substance is frequently detected in the environment (0.003-64 μg/L) as a result of water and sludge discharges from wastewaters treatment plants. Recently, [START_REF] Dan | Accelerated biodegradation of p-tertbutylphenol in the Phragmites australis rhizosphere by phenolic root exudates[END_REF] studied the accelerated biodegradation of p-tert-butylphenol in the Phragmites australis rhizosphere by phenolic root exudates. Their results showed that p-tert-butylphenol was initially adsorbed to root surface (56-83%), and subsequently degraded (17-44%) by rhizosphere microbes of Phragmites australis (conditions: 300 mL of solution containing 6.2-8.6 g of Phragmites australis and 10 mg/L of butylphenol; 25 °C; 70% humidity; 12 h/day light; experimental period of 16 days). The presence of certain phenolic root exudates (p-hydroxybenzoic acid, p-coumaric acid, caffeic acid and ferulic acid) at the same identical concentration (50 mg/L) is beneficial for the enrichment of p-tertbutylphenol degrading bacteria and then accelerates the biodegradation of the substance, the performances being classified in the following order: unit 2 (+ p-coumaric acid) > unit 1 (+ p-hydroxybenzoic acid) = unit 4 (+ ferulic acid) > unit 3 (+ caffeic acid) > unit 6 (sterile). [START_REF] Dan | Accelerated biodegradation of p-tertbutylphenol in the Phragmites australis rhizosphere by phenolic root exudates[END_REF] demonstrated the ability of phenolic root exudates with functional structures to accelerate the biodegradation of specific aromatic compounds by co-metabolism in the plant rhizosphere. However, the inherent process and mechanism remain insufficiently elucidated.

The removal of emerging contaminants by constructed wetlands is a recent area of study. Publications are numerous for pharmaceutical compounds but rarer for surfactants such as alkylphenols. This technology requires more research to achieve feasibility in terms of large-scale application to treat emerging substances. Further research is also necessary to evaluate the toxicity of the emerging pollutants to the plants and the respective carbon and nitrogen transformations that occurs in these complex root/solid/biofilm systems.

Alkylphenol Removal in Sequential Anaerobic-Aerobic Digestion of Sewage Sludge

Alkylphenol ethoxylates entering wastewater treatment plants are subjected to biotransformations producing alkylphenols (mainly nonylphenol) and their short chained ethoxylates (monoethoxylate and diethoxylate). These substances have been detected in effluents or adsorbed onto solids, but due to their hydrophobiclipophilic nature, proved by the high octanol-water partition values coefficient values (K ow ), they tend to accumulate in sewage sludge. Similar behaviour was also detected for their biodegradation products, which were found to be more persistent, lipophilic, and bioaccumulative than their parent compounds [START_REF] Venkatesan | National inventory of alkylphenol ethoxylate compounds in U.S. sewage sludges and chemical fate in outdoor soil mesocosms[END_REF]. The prevalent distribution of alkylphenol ethoxylates and related intermediates in sludge has a positive effect on the quality of wastewater treatment plant effluent, but raises serious concerns about sludge disposal practices, particularly for agricultural reuse. Enrichment of the resulting solid fraction occurs at concentrations several orders of magnitude higher than those of the influent wastewater [START_REF] Mailler | Fate of emerging and priority micropollutants during the sewage sludge treatment: case study of Paris conurbation. Part 1: contamination of the different types of sewage sludge[END_REF]. Accurate characterization of alkylphenol ethoxylates and their derivative compounds in sludge is therefore crucial to assess the environmental impact and safety of the agricultural reuse practice. Despite the relevance of the presence of these compounds in the solid fraction, previous studies in wastewater treatment plants were mainly focused on liquid streams and less attention was paid to their fate in the sludge treatment chain. Only recent studies have considered specific characterization of digested sludge for micropollutants and alternative processes in sludge treatment lines to improve their removal [START_REF] Braguglia | Quality assessment of digested sludges produced by advanced stabilization processes[END_REF][START_REF] Mailler | Fate of emerging and priority micropollutants during the sewage sludge treatment: case study of Paris conurbation. Part 1: contamination of the different types of sewage sludge[END_REF].

The environmental impacts of alkylphenol ethoxylates and their metabolites when sludge is reused in agriculture include direct uptake by crops and subsequent transfer into the food chain, raising serious concerns for human health and negative effects on plant growth. Their persistence and recalcitrance amplify and extend these effects over time, with long-term consequences that are difficult to predict. In addition, metabolites such as nonylphenol are capable of mimicking natural hormones and inducing endocrine disruption in aquatic and terrestrial organisms [START_REF] Soto | P-Nonyl-phenol: an estrogenic xenobiotic released from "modified" polystyrene[END_REF], which, through cultivation, can be recycled in the food chain.

The relevance of the alkylphenol ethoxylate content in the assessment of the environmental impact and safety of agricultural reuse of sewage sludge has been recognized by the European Union in the Working Documents on Sludge 3rd draft (EU-WDS, EU 2000) and on Sludge and Biowaste (EU-WDSB, EU 2010). They suggest for alkylphenol ethoxylates the limit value of 50 mg/kg dw , which is also applied in Sweden [START_REF] Rule | Sources of priority substances entering an urban wastewater catchment-trace organic chemicals[END_REF] and Turkey (Ömeroğlu et al. 2015), while Denmark prescribes a lower limit of 10 mg/kg dw [START_REF] Inglezakis | European Union legislation on sewage sludge management[END_REF].

Efficient sludge digestion is the key step in the sludge treatment chain to reduce the solid fraction and, at the same time, to improve the quality of the digested sludge in terms of content of toxic contaminants such as alkylphenol ethoxylates, pathogens and virus. The combination of two sequential, anaerobic-aerobic digestion steps has been proposed and investigated as effective strategy to improve the performance of the single anaerobic digestion process. The rationale behind this approach is that different reaction environments (anaerobic and aerobic) offer complementary and therefore optimal biodegradability conditions for the different solids fractions and contaminants in sludge [START_REF] Kumar | Effect of secondary aerobic digestion on properties of anaerobic digested biosolids[END_REF]. In order to improve the performance of the process in terms of reduction of solids content and removal of persistent contaminants, a modification of the sequential process has been proposed, namely the operation of the post-aerobic stage under mesophilic conditions (T = 37 °C) [START_REF] Tomei | Two-stage anaerobic and post-aerobic mesophilic digestion of sewage sludge: analysis of process performance and hygienization potentiality[END_REF]. Since anaerobically digested sludge is at mesophilic temperature (T = 37 °C) and exothermic reactions occur in aerobic digestion, little external energy input is required for the sequential digestion process.

In a recent comprehensive study on the fate of micropollutants in the anaerobicaerobic digestion process, [START_REF] Tomei | Post-aerobic treatment to enhance the removal of conventional and emerging micropollutants in the digestion of waste sludge[END_REF] analysed the fate of conventional and emerging substances, including alkylphenol ethoxylates. Experiments were conducted on real secondary sludge sampled in the aeration basin of a large-scale wastewater treatment plant (serving about 780,000 equivalent inhabitants). The sludge characterization in terms of classical parameters is reported in Table 4.4. The mean concentration of alkylphenol ethoxylates and related metabolites in secondary sludge throughout the experimental campaign was 2.66 ± 1.88 mg/kg dw , while the concentration range of the alkylphenol ethoxylates and related metabolites analysed (referring to the period when the tests were performed) is shown in Table 4.5 [START_REF] Tomei | Post-aerobic treatment to enhance the removal of conventional and emerging micropollutants in the digestion of waste sludge[END_REF].

The experimental apparatus consisted of two 7.4 L digesters operated in semicontinuous mode and in series: waste sludge was introduced into the anaerobic reactor (working volume 7 L) once a day and an equivalent volume of anaerobically digested sludge was fed to the next aerobic reactor (working volume 4.5 L). Both reactors were equipped with mechanical stirrers and a thermostatic jacket to maintain the process temperature. The anaerobic reactor was operated under mesophilic conditions (T = 37 °C) and with a sludge retention time of 15 days. The dissolved oxygen concentration in the aerobic reactor was controlled at ~3 mg/L and the aerobic sludge retention time was 12 days. A scheme of the sequential process, with additional detailed information on the laboratory-scale installation, is given elsewhere [START_REF] Tomei | Sequential anaerobic/anaerobic digestion for enhanced sludge stabilization: comparison of the process performance for mixed and waste sludge[END_REF]. Tests were conducted for both configurations: anaerobic mesophilic-aerobic at T = 20 °C (AA20) and anaerobic mesophilicaerobic at T = 37 °C (AA37).

The overall performance of the sequential process showed very good results in terms of volatile solids reduction with an average removal of 40-43% in the anaerobic phase and an additional aerobic removal of 18-30% for AA20 and AA37 respectively. Extensive data on the performance parameters of the sequential digestion in terms of solids and micropollutant removal are available in [START_REF] Tomei | Post-aerobic treatment to enhance the removal of conventional and emerging micropollutants in the digestion of waste sludge[END_REF]. With respect to the removal of alkylphenol ethoxylates and their metabolites, Fig. 4.10 shows the concentration pattern in the feed sludge and in digested sludge after anaerobic and aerobic digestion for the two operating conditions AA20 and AA37, while Table 4.6 shows the corresponding removal efficiencies. Despite the high removal of volatile solid, no accumulation is observed in the digested sludge for all compounds, but a steady decrease in concentration is detected in all stages of digestion process. Post-aerobic treatment provides additional removals that are more evident at higher temperature.

Of the alkylphenol ethoxylates analysed, 4-tert-nonylphenol remained below the limit of detection during the sequential process, while 4-n-octylphenol and 4-tertoctylphenol were completely removed during the anaerobic step. High anaerobic removals of 98.5 and 88.3% were also detected for 4-tert-octylphenol monoethoxylate and 4-nonylphenol, respectively. For ethoxylates compounds, a progressive decrease in anaerobic removal according to the complexity of the molecule was observed, reaching values of 29% for nonylphenol diethoxylate. In respect to the single anaerobic digestion, the post-aerobic step at 20 °C allowed significant additional removal in all cases, with values ranging from 32 to 81% for 4-nonylphenol and 4-tert-octylphenol monoethoxylate, respectively. Aerobic removals were improved by operating the digester at 37 °C with values varying from 64% for the less degradable 4-nonylphenol to 94% for 4-tert-octylphenol monoethoxylate. In the aerobic phase, there is not clear evidence of the correlation between removal efficiency and molecule complexity for the two temperatures studied.

The results of this study showed that the post-aerobic digestion step (after the conventional anaerobic digestion process) could improve the removal of alkylphenol ethoxylates and their metabolites with better results at the higher aerobic temperature (37 °C vs. 20 °C). Alkylphenol ethoxylates are characterized by high lipophilicity, which leads to their marked accumulation in sewage sludge. The high removal obtained in the sludge matrix by the sequential digestion process has therefore demonstrated the feasibility of this treatment strategy to obtain "cleaner" sludge suitable for safe agricultural reuse.

Removal of Alkylphenols by Advanced

Oxidation-Processes

Removal of Alkylphenols from Municipal Wastewater Using Ozone/Granular Activated Carbon

For downstream reduction in treatment plants, the proposed tertiary treatment for wastewater treatment is often the use of an ozonation step combined with an activated carbon adsorption step. Treatment using ozonation and adsorption on activated carbon is already used for the treatment of drinking water (ozone disinfection for the potabilization of surface or ground water). The oldest use of ozone is as a biocide in drinking water (it is currently known as one of the most efficient and fastest microbiocides). Ozone can also be used as the only technology or in combination with other processes with the aim, for example, of improving coagulation/ flocculation, biodegradability, or as a primary or secondary treatment in association with biological wastewater treatment.

Ozonation and adsorption processes differ fundamentally in the way they work: with ozone (generated on-site because it is unstable and decomposes to elemental oxygen in a short amount of time after generation), the substances are transformed by chemical processes, whereas the substances are adsorbed onto the coals by mainly physical mechanisms. Ozone as a strong oxidant can also be used in wastewater treatment to remove organic pollutants that are refractory to other treatments [START_REF] Rodríguez | Ozone-based technologies in water and wastewater treatment[END_REF]). However, although the number of works on the efficiency of ozone to eliminate organics is important, the use of ozone is less extended in wastewater treatments than in disinfection or in natural water treatments.

In a municipal wastewater treatment plant, the ozonation stage consists of using the oxidation capacities of ozone to destroy all organic molecules, including alkylphenols. It exploits the indirect radical reactions that take place during ozonation. In fact, the injection of ozone does not completely eliminate the pollutants present in the wastewater, but causes them to oxidize, which facilitates their further removal. Combined with activated carbon and/or sand filters, which traps the molecules that are refractory to ozonation, this treatment allows an overall organic pollutant reduction of 80%. The ozonation technology integrates well into existing municipal wastewater treatment plants and can be easily managed by its staff. Despite significant investments, this technology is already widely applied, e.g. in Switzerland and Germany. Indeed, the ozonation process is beginning to become widespread because it effectively removes many of the substances that threaten drinking water quality, fish reproduction and/or the survival of sensitive aquatic organisms, while having reasonable operating costs. Ozonation is also attractive for new developments, for example, in the water management, particularly in those where the objective is the reuse of wastewater. The important parameter of ozonation is the time period during which the ozone must remain in contact with the water in order to neutralize the pollutants. This time period is not without financial consequences (the faster the ozone treatment, the smaller the reactor). Ozone is an expensive oxidant and the necessary doses in wastewater treatments are higher than in surface or ground water, thus increasing operational cost [START_REF] Rodríguez | Ozone-based technologies in water and wastewater treatment[END_REF].

Ozone is a strong oxidant and a virucide that is capable of reacting through wellknown reaction mechanisms (it attacks electron rich structures in molecules), that depends on process parameters such as pH, presence of other substances and type/ structure of the pollutants [START_REF] Hoigne | Rate constants of reactions of ozone with organic and inorganic compounds in water. I: non-dissociating organic compounds[END_REF][START_REF] Sánchez-Polo | Efficiency of activated carbon to transform ozone into OH radicals: influence of operational parameters[END_REF]. Ozonation may take place by the direct reaction of the ozone molecule with the target substance or by means of hydroxyl radicals produced during the decomposition of ozone in aqueous media. In practice, both direct and indirect reactions take place simultaneously, excepted when an oxidation process is specifically designed to enhance the concentration of hydroxyl radicals in a solution (case of an advanced oxidation process). Several significant works demonstrated that ozonation efficiently reduced the concentrations of many trace organic compounds present in secondary wastewater effluents, including pharmaceuticals and alkylphenols [START_REF] Ternes | Ozonation: a tool for removal of pharmaceuticals, contrast media and musk fragrances from wastewater[END_REF][START_REF] Huber | Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: a pilot study[END_REF][START_REF] Hollender | Elimination of organic micropollutants in a municipal wastewater treatment plant upgraded with a full-scale post-ozonation followed by sand filtration[END_REF][START_REF] Wert | Effect of ozone exposure on the oxidation of trace organic contaminants in wastewater[END_REF][START_REF] Zucker | A hybrid process of biofiltration of secondary effluent followed by ozonation and short soil aquifer treatment for water reuse[END_REF] through direct and indirect oxidation reactions. [START_REF] Ribeiro | An overview on the advanced oxidation processes applied for the treatment of water pollutants defined in the recently launched Directive 2013/39/EU[END_REF] summarized data published over the last decade on the application of advanced oxidation processes for the elimination of priority substances and certain other pollutants defined in the European Directive. Advanced oxidation processes generate highly oxidizing and non-selective species such as hydroxyl radical, being particularly interesting for the treatment of effluents containing emerging pollutants (Fig. 4.11).

The application of the ozonation process to improve the biodegradability of alkylphenol ethoxylates began in the late 1970s [START_REF] Narkis | Ozonation of non-ionic surfactants in aqueous-solutions[END_REF]. Although ozonation itself reduced chemical oxygen demand by only 39% and total organic carbon by 16%, it significantly improved the biodegradability of nonylphenol ethoxylates by altering their molecular structure. The elimination of chemical oxygen demand was as high as 70% and the removal of total organic carbon was 62.5% by biodegradation after the ozonation process, while the reduction without ozonation was 25% of chemical oxygen demand and 23% of total organic carbon. The optimum pH for the degradation of alkylphenol ethoxylates by ozone was 9 (indirect radical reactions favored), and it appears that the primarily attack takes place on the polyethoxylate chain and not the aromatic ring. Ning et al. (2007a, b) showed that the ozonation process was an appropriate tool for the degradation of nonylphenol and octylphenol. They investigated the degradation of these two alkylphenols in an acidic environment, i.e. a direct reaction of ozone. Studied contaminants were relatively easily degraded by ozonolysis. Based on the results of the study on the reaction mechanism of the nonylphenol oxidation with ozone, it is assumed that the aliphatic chain of the alkylphenols no longer has a significant effect on the behavior of these compounds during ozonation. The primary product is hydroxyl-alkylphenol, which is formed by attacking the aromatic ring in the ortho position with ozone and then by the addition of hydroxyl groups.

Based on the reaction mechanism study, the initial product of ozonation appears to be hydroxyl alkylphenol. Kim et al. (2005b) previously reported that the dominant ozonation products of nonylphenol were acetaldehyde and formaldehyde. [START_REF] Zhang | Ozonation of nonylphenol and octylphenol in water[END_REF] also studied the degradation of nonylphenol and octylphenol in aqueous solutions containing acetonitrile to improve the solubility of alkylphenols by ozone. The authors conducted experiments to test the effects of initial pH, alkylphenol concentrations and ozone dosage on removal efficiency. Complete removal of nonylphenol and octylphenol was obtained after 6 min of ozonation at pH 9. Experiments at pH 6.5 showed that the amount of ozone required for degradation is higher when the degradation efficiency of nonylphenol was nearly 42% with an ozone dosage of 0.13 mg/min, whereas with an ozone dosage nearly three times higher, the degradation efficiency increased to 96%. It was concluded that the higher the initial alkylphenol concentration, the lower the degradation efficiency of alkylphenol. [START_REF] Baig | Ozone oxidation of oestrogenic active substances in wastewater and drinking water[END_REF] examined the matrix effect of wastewater during ozonation of octylphenol and nonylphenol. The data obtained indicated that the wastewater matrix significantly affected the ozonation kinetics, but did not change the corresponding reactivity scale. The dose of ozone required for complete degradation of these substances was increased, but a usual dose of 12 mg/L was sufficient for sufficient degradation. The ozonation process proved to be an effective solution to treat secondary waste water containing the mentioned oestrogenic active substances.

The study by [START_REF] Bertanza | Removal of BPA and NPnEOs from secondary effluents of municipal WWTPs by means of ozonation[END_REF] on the removal of nonylphenol from wastewater treatment plants showed that these conventional systems cannot achieve the very low concentrations required, and therefore additional treatment such as ozonation was necessary. The authors carried out experiments with wastewater from an Italian wastewater treatment plant in Verona and concluded, that ozonation was an economically viable solution as a tertiary step and a promising technology to reduce pollutants emissions. Similar conclusion was reported by [START_REF] Schaar | Micropollutant removal during biological wastewater treatment and a subsequent ozonation step[END_REF] and [START_REF] Ibáňez | Removal of emerging contaminants in sewage water subjected to advanced oxidation with ozone[END_REF]. [START_REF] Schaar | Micropollutant removal during biological wastewater treatment and a subsequent ozonation step[END_REF] reported a significant reduction in toxicity and pollutant emissions at the outlet of an actual wastewater treatment plant by ozonation. [START_REF] Grandclement | From the conventional biological wastewater treatment to hybrid processes, the evaluation of organic micropollutant removal: a review[END_REF] considered promising hybrid biological processes to remove pollutant as well as a combination of biological and physicochemical or chemical processes.

In Switzerland, a new law to reduce the discharge of pollutants from wastewater treatment plants came into force in 2016 to protect ecosystems and sources of drinking water [START_REF] Böhler | Projekt ReTreat. Untersuchungen zu verfahren für die biologische nachbehandlung nach ozonung[END_REF][START_REF] Bourgin | Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products[END_REF]. The Neugut wastewater treatment plant (equivalent to 150,000 people, Dübendorf) was the first wastewater treatment plant in Switzerland to implement long-term ozone treatment. The following treatment steps are used: mechanical treatment with preliminary clarification, biological treatment, ozonation, and sand filtration with possible post-precipitation. Sewage sludge is then treated by mesophilic anaerobic digestion, dewatered and transported to an incineration plant. Among filtration methods, the most effective is sand filtration which removes dissolved organic carbon, assimilable organic carbon and total suspended solids. However, filtration with fresh activated carbon is a better treatment as finishing step after ozonation, resulting in a significant reduction of organic compounds [START_REF] Bourgin | Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products[END_REF]. Monitoring of 550 substances including alkylphenols confirmed that an average reduction of >80% (up to >84% for a shortlist of 12 indicator substances established by the Swiss Federal Office for the Environment which requires an elimination performance of 80% for these substances) was achieved through a combined advanced treatment. The process uses a low ozone concentration of 3.5 mg/L, which is sufficient to effectively remove emerging substances and meet regulatory requirements, while also keeping operating costs low. After ozonation (the system is installed in the filtration reactor), additional filtration treatment is necessary to avoid possible negative ecotoxicological effects due to oxidation by-products (e.g. bromate, nitrosamines, metabolites). Positive effects of ozone treatment have indeed been demonstrated by in vivo and in vitro bioassays. The authors concluded that ozonation and activated carbon adsorption is a recommended technology that lead costefficiently to a significant abatement of the pollutant load and toxicity.

So, it has been proven that the removal of nonylphenol from wastewater could be improved by adding supplementary steps such as activated carbon filtration, ultraviolet treatment and ozonation to existing treatment processes [START_REF] Johnson | Comparing steroid estrogen and nonylphenol content across a range of European sewage plants with different treatment and management practices[END_REF].

Attention is paid to these potential solutions, although these could be expensive and did not provide always a final solution due to the accumulation of pollutants in the sludge [START_REF] Jones | Questioning the excessive use of advanced treatment to remove organic micropollutants from wastewater[END_REF]). However, additional ozonation of surplus sludge could also results in increased removal of endocrine disrupting compounds absorbed in the sludge [START_REF] Shao | Nonylphenol and nonylphenol ethoxylates in river water, drinking water, and fish tissues in the area of Chongqing, China[END_REF][START_REF] Qiang | Degradation of endocrine-disrupting chemicals during activated sludge process[END_REF]. [START_REF] Qiang | Degradation of endocrine-disrupting chemicals during activated sludge process[END_REF] reported that ozonation was an effective means for excess sludge reduction. Indeed, sludge-bound pollutants were effectively removed during sludge ozonation. Ozone treatment was suitable for the degradation of endocrine disrupting compounds, such as 4-nonylphenol, estrone, estriol, 17α-ethynylestradiol, and bisphenol A. Results indicated that the emerging substances present in activated sludge could be effectively removed by ozone even though the apparent rate constants in sludge were 3-4 orders of magnitude lower than those in water. This technology was considered as environmentally friendly.

A drawback of ozonation is the insufficient mineralization of pollutants. However, total mineralization with ozone is very expensive. Thus, newly developed processes use ozone only for the removal of toxic compounds and/or partial oxidation of resistant organic pollutants from wastewater. Controlled ozonation processes which are applied can inactivate inhibitory compounds in biological wastewater treatment and improve the biodegradability of recalcitrant organic matter by modifying its chemical structure. The extent of this partial oxidation should only be sufficient to facilitate subsequent biodegradation of the transformed organic matter. The combination of ozonation with homogeneous or heterogeneous catalysis which can increase the production of hydroxyl radicals can be one of the solutions. Another possibility is to use ozone in combination with other techniques such as ultrasonic/ UV radiation, hydrogen peroxide, or other hybrid methods [START_REF] Fujita | Adsorption and decomposition of water-dissolved ozone on high silica zeolites[END_REF][START_REF] Gogate | A review of imperative technologies for wastewater treatment II: hybrid methods[END_REF][START_REF] Johnson | Comparing steroid estrogen and nonylphenol content across a range of European sewage plants with different treatment and management practices[END_REF][START_REF] Li | Comparison of AC/O 3 eBAC and O 3 eBAC processes for removing organic pollutants in secondary effluent[END_REF][START_REF] Jones | Questioning the excessive use of advanced treatment to remove organic micropollutants from wastewater[END_REF][START_REF] Rodríguez | Ozone-based technologies in water and wastewater treatment[END_REF][START_REF] Alvarez | The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach[END_REF][START_REF] Poyatos | Advanced oxidation processes for wastewater treatment: state of the art[END_REF][START_REF] Vatankhah | Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent[END_REF]. Many examples can be found in two comprehensive reviews published by [START_REF] Rodríguez | Ozone-based technologies in water and wastewater treatment[END_REF] and by [START_REF] Poyatos | Advanced oxidation processes for wastewater treatment: state of the art[END_REF].

The performances of O 3 -H 2 O 2 couple on the biodegradability of nonylphenol ethoxylates was investigated by [START_REF] Adams | Biodegradation of nonionic surfactants and effects of oxidative pretreatment[END_REF]. The results showed that these substances were oxidized to shorter polyethoxylate chains, although biodegradability was not improved with a low dosage of ozone and hydrogen peroxide. In order to achieve a reduction of at least 80% of dissolved organic carbon, 7 mg of absorbed ozone per mg of nonylphenol ethoxylates was required. The possibility of the formation of toxic oxidation byproducts was not excluded but was not explicitly investigated.

The study on oxidation kinetics of nonylphenols and nonylphenol ethoxylates carried out by [START_REF] Hyunook | Oxidation of nonylphenol in water using O 3[END_REF] showed that the degradation efficiency increased significantly when ozone and hydrogen peroxide were combined. The authors demonstrated that nonylphenol and its derivatives can be effectively oxidized over a pH range of 5 to 9. At pH 7, the efficiency was even greater than 90%.

Wastewater at the outlet of the municipal wastewater treatment plant has been treated using several ozone-based processes by [START_REF] Rivas | Wastewater recycling: application of ozone based treatments to secondary effluents[END_REF]. The application of ozone as the sole oxidizing agent was capable of halving the initial chemical oxygen demand (35 mg/L at a flow rate of 40 L/h) with a degree of mineralization of approximately 40%. The ozone/hydrogen peroxide system significantly improves the performance of the oxidation process, increasing the degree of mineralization up to 70% (35 mg/L ozone at a flow rate of 40 L/h in the presence of 0.01 M hydrogen peroxide). The simultaneous application of ozone and UV radiation showed beneficial effects on both the chemical oxygen demand removal rate and total organic carbon conversion compared to ozone alone. However, compared to the ozonation alone, no improvement was observed for combination of ozone with commercial activated carbon. On the contrary, [START_REF] Li | Comparison of AC/O 3 eBAC and O 3 eBAC processes for removing organic pollutants in secondary effluent[END_REF] showed that the presence of granular activated carbon during ozonation (ozone/activated carbon) improved oxidation efficiency through increased conversion of ozone to hydroxyl radicals. [START_REF] Alvarez | The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach[END_REF] studied the effect of ozone/activated carbon at pilot-scale on the removal of pollutants from municipal wastewater. The results showed that the simultaneous use of ozone and granular activated carbon initially improved the removal of ozone-refractory pollutants. However, the promoting effect of ozone and activated carbon decreased over time. The technology uses the advantage of the high adsorption capacity of activated carbon for pollutant removal [START_REF] Rivera-Utrilla | Activated carbon modifications to enhance its water treatment applications. An overview[END_REF]. Activated carbon also serves as an initiator of ozone decomposition (a role that can also occur with other types of catalysts), which increases the formation of hydroxyl radicals [START_REF] Hoigne | Chemistry of aqueous ozone and transformation of pollutants by ozonation and advanced oxidation processes[END_REF][START_REF] Alvarez | The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach[END_REF]. The mechanism of this catalytic ozonation is not completely elucidated [START_REF] Jans | Activated carbon and carbon black catalyzed transformation of aqueous ozone into OH-radicals[END_REF][START_REF] Sánchez-Polo | Efficiency of activated carbon to transform ozone into OH radicals: influence of operational parameters[END_REF][START_REF] Alvarez | The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach[END_REF]). [START_REF] Jans | Activated carbon and carbon black catalyzed transformation of aqueous ozone into OH-radicals[END_REF] reported that the reaction of ozone with activated carbon was a catalytic reaction. However, the work of [START_REF] Sánchez-Polo | Efficiency of activated carbon to transform ozone into OH radicals: influence of operational parameters[END_REF] showed that activated carbon acted more like a classical initiator during ozonation. The overall efficiency of the ozone/activated carbon depended largely on the characteristics of the activated carbon and the wastewater matrix.

The role of carbon as a catalyst, promoter or initiator is still a subject of debate. [START_REF] Vatankhah | Simultaneous ozone and granular activated carbon for advanced treatment of micropollutants in municipal wastewater effluent[END_REF] investigated the effectiveness of simultaneous ozone and granular activated carbon in removing environmentally relevant substances from wastewater. In contrast to previous publications, which provided the results of shortterm experiments (1-3 h), this work focused on evaluating the robustness of ozone/ granular activated carbon in a long-term experiment (up to 20 h). The results showed that this combination improved the reduction of some pollutants compared to ozone in only 20 h of operation. However, its overall efficiency decreased significantly after prolonged exposure to ozone, indicating that granular activated carbon did not contribute as a catalyst. The use of ozone initially resulted in an increase in the BET surface area of the granular activated carbon (mainly micropores), which improved the adsorptive removal of the pollutants studied. However, exposure to ozone eventually caused structural damage to the surface of the granular activated carbon leading to a reduction of the BET surface area in the later stages and to a significant decrease of overall efficiency.

An alternative ozonation process using zeolite-based adsorbents has been proposed by [START_REF] Fujita | Adsorption and decomposition of water-dissolved ozone on high silica zeolites[END_REF]. Organic pollutants and ozone can be adsorbed in the zeolite micropores. As a result, concentrations in micropores become much higher than those in the mass phase and the apparent reaction rate may be increased. [START_REF] Derco | Removal of alkylphenols from real wastewater using O 3 and O 3 /GAC. 7th European meeting on Chemical industry and Environment[END_REF][START_REF] Derco | Removal of alkylphenols from industrial and municipal wastewater[END_REF] studied the removal of nonylphenol, octylphenol and alkylphenol ethoxylates from industrial and municipal wastewater treatment. The main objective of the work was to investigate an alternative wastewater treatment process in the event of a production expansion and a consequent increase in alkylphenol releases. In this purpose, the capacity of the municipal wastewater treatment plant (which include secondary treatment) located closest to the industrial facility releasing alkylphenols was assessed. And ozonation and combined ozone/granular activated carbon processes were investigated as possible tertiary treatment step for the municipal wastewater treatment plant, or as end-of-pipe industrial wastewater treatment. It must be noted that before discharge to municipal sewers, industrial wastewater containing alkylphenols is subject of a pre-treated by coagulation with FeCl 3 and zeolite adsorption. Higher efficiencies were obtained when the ozonation is applied in industrial wastewater treatment (before discharge to municipal sewers), with target pollutants conversions greater than 90% for 2 h treatment time, except for 4-tert-octylphenol. The highest conversion, 98% was obtained for octylphenol ethoxylates. However, a great variability in ozonation performance was observed for both industrial and municipal wastewaters, depending on sampling time. For example, nonylphenol ethoxylates showed the highest variability of the removal efficiency values (3.0-92.7%). Significantly higher volumetric ozone consumption was observed for industrial treatment compared to ozonation of municipal wastewater due to higher organic pollution. Negligible differences were observed for the removal of nonylphenol and nonylphenol ethoxylates when comparing ozone and ozone/granular activated carbon processes carried out under the same conditions. On the other hand, a significantly higher removal/degradation rate of octylphenol ethoxylates was observed with the ozone/granular activated carbon process compared to the ozone alone. A lower toxicity impact of ozonation treatment intermediates and products on Vibrio fisheri was measured compared to the ozone/granular activated carbon. It worth mentioning that residual concentrations of nonylphenol and nonylphenol ethoxylate in all analyzed samples from municipal wastewater treatment plants complied with the limits of the environmental quality standards (Directive 2008/105/EC).

Besides activated carbon, Mn and Fe modified zeolites have been tested in the oxidative degradation of alkylphenols in industrial wastewater [START_REF] Urminska | Utilization of ozonization and adsorption ozonization in the treatment of industrial waste water containing alkylphenols[END_REF]. As can be seen from the data presented in Fig. 4.12, both materials improved the ozonation efficiency in terms of target pollutants removal and dissolved organic carbon (DOC) and chemical oxygen demand (COD) abatement. However, the performance of the oxidation process with these two modified zeolites was lower than that of activated carbon assisted ozonation. For better comparison of the activity and selectivity of the proposed materials in alkylphenols removal, an assessment of the adsorption and oxidation contributions to the overall process must be done. The highest chemical oxygen demand decrease and removal of dissolved organic carbon were observed during the first 5-10 min of the ozone/granular activated carbon process (Figs. 4.13 and 4.14). A higher proportion of readily oxidizable organic matter (0.73) was calculated for chemical oxygen demand compared to 0.62 for dissolved organic carbon. These results demonstrated that ozonation in combination with activated carbons is a feasible method for oxidation of alkylphenols, and also effective for chemical oxygen demand and total organic carbon reduction.

The survey of literature shows that the catalytic mechanism of activated carbon ozonation is not yet clear, but most of the results suggest that the role played by the carbon is essentially to promote the decomposition of ozone with a subsequent increase in the production of radicals. Consequently, activated carbon would behave as an initiator of the radical-type chain reaction that transforms ozone into hydroxyl radicals. Ozonation on other materials such as supported metals has been less studied for the treatment of real industrial or municipal wastewaters but is a research topic in full development. So far, only ozone technologies coupled with carbon adsorption and/or filtration steps have been widely used in drinking water treatment plants, e.g. in France, to treat residual organic pollution and pathogens, in order to meet regulatory requirements. This is also a growing market for wastewater treatment, particularly in Switzerland and Germany, e.g. to treat pharmaceuticals, hormones and industrial products (alkylphenols). Indeed, ozone/carbon or ozone/sand coupling is both technologically simple to implement on an existing treatment plant, effective in reducing the pollutant load and pathogens, and economically viable (relatively low operating and maintenance costs). Nevertheless, other so-called advanced oxidation methods (sonochemical methods, photolysis, photocatalysis, electrochemistry, Fenton process) or membrane filtration (the price of membranes has decreased significantly, as have the maintenance costs of this technology) are under development and could compete with the ozone/activated carbon or ozone/sand coupling. In all cases, pilot experiments are needed to demonstrate not only the chemical efficiency of the integrated processes but also the economic viability.

Electrochemical Degradation of Alkylphenols

A viable alternative for the degradation of alkylphenols or their polyethoxylates in wastewater and other environmental samples are electrochemical techniques. These can be broadly divided into classical, e.g. electrocoagulation, electrofiltration, and also electrooxidation. The latter, however, is nowadays more often classified among electrochemical advanced oxidation processes, mainly because of the use of modern electrodes. Other modern electrochemical approaches are electro-Fenton, photoelectrooxidation, and combination of electrodegradation with ozonation and other chemical oxidants. In the following overview, the research in this field is presented, mainly for the last 10 years. The detailed parameters of the electrochemical treatments are given in Table 4.7, while general descriptions and comparison of treatments are given below.

As one of the classical electrochemical treatment options, electrocoagulation is nowadays less often used for the removal of emerging contaminants. Nevertheless, it was applied to remove nonylphenol polyethoxylate (9 ethoxylate units) from synthetic solutions and hospital wastewater [START_REF] Henriques | Nonylphenol polyethoxylate in hospital wastewater: a study of the subproducts of electrocoagulation[END_REF]. The electrochemical cell consisted of two aluminum electrodes with a surface of 2400 mm 2 . NaCl was added to the solution as a supporting electrolyte. The removal of the pollutant was performed at 1.5 A and 60 °C and was monitored by high-performance liquid chromatography with fluorescence detection, while the transformation products were identified by liquid chromatography-mass spectrometry. Moreover, chemical oxygen demand and biodegradability (by manometric respirometry test) were measured. The removal followed a pseudo-first-order kinetics. After 30 min of treatment, 95% of the pollutant was removed from synthetic and 89% from hospital wastewater, although the chemical oxygen demand decreased in the latter only by 26%. Liquid chromatographic-mass spectrometric analysis revealed the formation of degradation products with shorter ethoxylate chain (1-2 units), alkylphenoxy ethoxyacetic acid, and alkylphenoxy acetic acid. The biodegradability test initially performed better in the treated solution, but after 28 days reached the same level as in the untreated solution, i.e. 32-36%. Therefore, [START_REF] Henriques | Nonylphenol polyethoxylate in hospital wastewater: a study of the subproducts of electrocoagulation[END_REF] concluded that both treated and untreated samples are not readily biodegradable, probably because only partial degradation into transformation products occurred.

A more recent study on electrocoagulation was published by [START_REF] Cook | Removal of six estrogenic endocrine-disrupting compounds (EDCs) from municipal wastewater using aluminum electrocoagulation[END_REF]. They applied an electrocoagulation approach using aluminum blades as electrodes for the removal of six endocrine-disrupting (xenoestrogenic) chemicals from spiked influent wastewater and tertiary-treated effluent from a communal wastewater treatment plant. The reaction cell consisted of nine aluminum blades with a total volume of 221.2 cm 3 with appropriate connections to obtain two anodes and one cathode. At the anode, aluminum (III) ions were generated, while hydroxide ions were produced at the cathode. Precipitated Al(OH) 3 adsorbed organic pollutants present in wastewater which was percolated through the cell by the aid of a peristaltic pump. Several parameters were optimized: voltage range, electric current range, arrangement of electrodes, retention time of wastewater in the cell, and cleaning procedure for electrodes. The efficacy of the treatment was monitored by gas chromatographic-mass spectrometric analysis preceded by solid phase extraction and derivatization to trimethylsilyl derivatives. After 20 min of treatment at retention time of wastewater 2 min/L, the removal of nonylphenol was 81% in influent wastewater and as high as 98% in tertiary-treated effluent wastewater. In fact, nonylphenol showed the highest removal ratio of all the studied compounds, which included bisphenol A and estradiol analogues. The study demonstrated high removal efficiency for nonylphenol. However, there was no attempt to elucidate the mechanism of its removal or possible transformation products.

Advanced electrochemical oxidation is one of the most frequently applied electrochemical processes for removing pollutants from wastewater. Electrooxidation of nonylphenol ethoxylate was studied by [START_REF] Armijos-Alcocer | Electrochemical degradation of nonylphenol ethoxylate-7 (NP7EO) Using a diaclean (R) cell equipped with boron-doped diamond electrodes (BDD)[END_REF]. They employed a DiaClean® electrochemical cell which is characterized by superior performance in terms of mass transfer, current distribution, and hydrodynamics. The cell was equipped with boron-doped diamond electrode with the surface area of 70 cm 2 as anode and a stainless steel cathode of the same area, and was operated in a galvanostatic mode. Nonylphenol ethoxylate was added in an initial concentration of 500 mg/L and the solution was circulating in the cell by the aid of a peristaltic pump. The tested electrolyte was either an acetate buffer (0.5 M, pH 4.0) or an ammonia buffer (0.1 M NH 3 + 0.05 M HCl, pH 9.25). With the former, cyclic voltammetry showed that a cathodic reduction occurs as well, causing a regeneration of the pollutant. In alkaline media, the oxidation was irreversible, but it was necessary to apply anodic potential above 1.0 V. It was concluded that both direct and indirect oxidation by hydroxyl radicals occurred. Authors also studied the effect of current density and electrolyte flow and determined the optimal conditions to be 40 mA/cm 2 and 12.6 L/min, respectively. The effectiveness of the treatment was monitored by measuring total organic carbon, chemical oxygen demand and absorbance of the solution at 200-500 nm. From the changes in UV spectra during the treatment, authors concluded that quinone and hydroquinone oxidation by-products were formed and then further degraded. Under optimal conditions, total organic carbon decreased by 90% after 8 h of treatment. Finally, Armijos-Alcocer et al. ( 2017) provided the operational cost analysis and concluded that electrochemical oxidation would be a feasible approach to remove nonylphenol ethoxylates from wastewater.

Electrooxidation of nonylphenol decaethoxylate was studied by Vences-Benitez et al. ( 2017) as well, both in aqueous solution and in textile industry wastewater. Three different electrode configurations were tested: boron-doped diamond anode combined with copper, iron, or boron-doped diamond cathode, and the supporting electrolyte was Na 2 SO 4 . Besides, the current density and pH of the solution were optimized as well. Total organic carbon, chemical and biochemical oxygen demand were monitored. Additionally, UV/Vis and IR spectra were taken before and after the treatment. Hydrogen peroxide concentration was also measured during the process. Cu and Fe cathodes were chosen because a small amount of the material was dissolved in an electrochemical system, resulting in a catalytic production of H 2 O 2 . In aqueous solutions, total organic carbon reduction (as a measure of mineralization) after 4 h was 39.7% with boron-doped diamond cathode, 45.6% with Cu cathode, and 31.8% with Fe cathode. Optimal current density was either 3 or 6 mA/cm 2 , while pH differed between the systems used. For textile wastewater, total organic carbon decrease was 26.5% and 37% for boron doped diamond and Cu cathode, respectively, while the system with Fe cathode was less efficient because the dissolved iron reacted with hydroxide and phosphate ions. However, an interesting finding was that the biodegradability of the treated wastewater was decreased in all three systems, as evaluated from the biochemical to chemical oxygen demand ratio. Finally, Vences-Benitez et al. ( 2017) estimated the consumption and cost of the energy for the optimal treatment system.

Parameters of the electrooxidation process on boron-doped diamond anode were studied for the removal of nonylphenol ethoxylate from synthetic and real wastewater [START_REF] Sivri | Electrooxidation of nonylphenol ethoxylate-10 (NP10E) in a continuous reactor by BDD anodes: optimisation of operating conditions[END_REF]. The cathode was made of stainless steel. Authors studied the effect of the supporting electrolyte (Na 2 SO 4 or NaCl), initial pH, current density, and electrolysis time by response surface methodology. They monitored total organic carbon, chemical oxygen demand and concentration of the pollutant, the latter by ready-to-use-kit. The optimal treatment conditions were found to be initial pH 8, current density 250 A/m 2 , and treatment time 45 min. In a NaCl electrolyte, the process was more efficient and fitted well to the zero-order kinetic model compared to the first-order model for Na 2 SO 4 . However, Na 2 SO 4 was a better choice for real wastewater, presumably because this sample already contained a significant concentration of chloride ions. In synthetic wastewater, 85.3% of nonylphenol ethoxylate was removed under optimal conditions, while the other two monitored parameters diminished by 92-94%. Similar removal percentages were achieved in real spiked wastewater. [START_REF] Sivri | Electrooxidation of nonylphenol ethoxylate-10 (NP10E) in a continuous reactor by BDD anodes: optimisation of operating conditions[END_REF] concluded that NaCl was a better choice for the supporting electrolyte because of the lower cost of treatment. However, no transformation products were monitored in this study.

Mediated electrochemical oxidation combines electrooxidation with the addition of a chemical oxidant. [START_REF] Rodriguez-Pena | Nonylphenol degradation by simultaneous electrooxidation on BDD anode and oxidation by H 2 O 2 in a continuous flow electrochemical reactor[END_REF] applied electrooxidation on boron-doped diamond anode either alone or combined with oxidation by H 2 O 2 for the removal of nonylphenol from simulated wastewater. A DiaClean® reactor was used with boron-doped diamond electrode on silicon as anode/working electrode and a stainless steel cathode. The electrolyte was H 2 SO 4 . The reactor was operating in a recirculation mode by means of a peristaltic pump. The process was followed by total organic carbon, chemical oxygen demand, UV/Vis spectrometry (200-600 nm), and consumption of H 2 O 2 . The dose of hydrogen peroxide was optimized to allow for the maximal production of hydroxyl radicals and avoiding the production of less reactive hydroperoxyl radicals. Under optimal conditions, i.e. pH 3, current density 30 mA/cm 2 , flow rate 7 L/min, 2 h of treatment and peroxide addition 1.0 mL/L, nonylphenol removal was 97.6% as determined by chemical oxygen demand and total organic carbon measurements. To show the applicability of their approach for the treatment of wastewater, [START_REF] Rodriguez-Pena | Nonylphenol degradation by simultaneous electrooxidation on BDD anode and oxidation by H 2 O 2 in a continuous flow electrochemical reactor[END_REF] calculated the operational costs as well. However, it should be noted that the process was tested only on synthetic solutions with no interfering substances.

Another example of mediated electrochemical oxidation is given in a paper by [START_REF] Setiyanto | Mediated electrochemical oxidation (MEO) process: a study on nonylphenol ethoxylates (NPE) oxidation in batch mode using cerium (IV) oxidant[END_REF]. They studied electrochemical oxidation with and without addition of an oxidant, cerium(IV) ions, for the removal of nonylphenol ethoxylate. The optimized parameters were the potential difference, electrolyte concentration, concentration of pollutant, concentration of Ce(III) ions, and oxidation time. Ce(III) ions were oxidized to Ce(IV), which in turn oxidized the nonylphenol ethoxylate. The maximum removal was obtained with 0.015 M Ce(III) in the electrolyte 0.2 M H 2 SO 4 , and the potential 6 V. With treatment time 1.5 h, the removal was 80-90%, but it was even slightly higher in the absence of Ce(III) ions. [START_REF] Setiyanto | Mediated electrochemical oxidation (MEO) process: a study on nonylphenol ethoxylates (NPE) oxidation in batch mode using cerium (IV) oxidant[END_REF] offered no explanation for this finding. The information on the measurement method for the concentration of the pollutant is missing as well.

The most interesting studies are those that show the effectiveness of a certain treatment approach under realistic conditions. Raw laundry wastewater was treated with a sequential system (Khosravanipour [START_REF] Mostafazadeh | Development of combined membrane filtration, electrochemical technologies, and adsorption processes for treatment and reuse of laundry wastewater and removal of nonylphenol ethoxylates as surfactants[END_REF], beginning with ultrafiltration and continuing with one of the following: adsorption processes on granular activated carbon or polymeric resin, nanofiltration, or electrooxidation. Additionally, the concentrate after ultra-or nanofiltration was treated by electrocoagulation and electrooxidation. Authors monitored total suspended solids, turbidity, chemical oxygen demand, and concentration of nonylphenol ethoxylates with different chain lengths (by solid-phase extraction and liquid chromatography-tandem mass spectrometry). For electrooxidation, a two electrode system was applied with grid anode (boron-doped diamond, Ti/Pt, and Ti/IrO 2 ) and cathode (graphite, vitreous carbon, and stainless steel). For electrocoagulation, an iron or aluminum anode was used, and a stainless steel or graphite cathode. Na 2 SO 4 was used as the electrolyte in all cases. The most efficient processes for nonylphenol ethoxylates removal were adsorption on both types of sorbents, nanofiltration, and electrooxidation of the nanofiltrate, as well as of the concentrate after nanofiltration. The boron-doped diamond electrode showed the highest percentage of removal. Electrocoagulation was less efficient, especially for longer-chained nonylphenol ethoxylates, presumably because of decreased adsorption on flocs due to increased hydrophobicity. Thus, the most efficient process to apply for regeneration of laundry wastewater was nanofiltration, which reduced all monitored parameters by 80%. The concentrate that contained a high concentration of nonylphenol ethoxylates could be successfully treated by electrooxidation.

Another interesting study was performed by [START_REF] Niu | Novel electrochemical pretreatment for preferential removal of nonylphenol in industrial wastewater: biodegradability improvement and toxicity reduction[END_REF]. They designed a novel molecular imprinted high-index facet SnO 2 (MI-SnO 2, HIF ) electrode and applied it for specific removal of nonylphenol from tannery wastewater before the biological treatment. A three-electrode system was used with the mentioned working electrode, a Pt counter electrode, a saturated calomel reference electrode, and with Na 2 SO 4 as a supporting electrolyte. In addition to MI-SnO 2, HIF , three other novel electrodes, namely NI-SnO 2, HIF (non-imprinted high-index facet SnO 2 ), MI-SnO 2, SG (molecular imprinted sol-gel SnO 2 ) and NI-SnO 2, SG (non-imprinted solgel SnO 2 ) were tested. The purpose was to preferentially remove toxic and nonbiodegradable chemicals from the majority of the biodegradable substances and thus improve biodegradability and decrease the estrogenic potential of wastewater. After 8 h of treatment at an electrode voltage of 1.8 V with the MI-SnO 2, HIF electrode, 95% of nonylphenol was removed, while the other two electrodes were less efficient. The predominant mechanisms were adsorption and subsequent oxidation at the electrode. The oxidation products were identified by liquid chromatographytandem mass spectrometry. Three degradation pathways were also proposed, leading to the mineralization of the pollutant. Additionally, the ratio of biological oxygen demand to chemical oxygen demand increased from 0.186 to 0.412, showing increased biodegradability. The estrogenicity of wastewater was determined by an enzyme-linked immunosorbent assay and had fallen to zero after 5 h of treatment with the chosen electrode. This approach to treat wastewater by preferential electrooxidation before biological treatment has shown undisputable advantages over the more common reverse approach [START_REF] Niu | Novel electrochemical pretreatment for preferential removal of nonylphenol in industrial wastewater: biodegradability improvement and toxicity reduction[END_REF].

Wastewater sludge is a by-product of wastewater treatment by biological degradation. It can contain significant amounts of more recalcitrant pollutants. [START_REF] Barrios | Electrooxidation treatment for removal of emerging pollutants in wastewater sludge[END_REF] tested the electrooxidation of sludge from industrial wastewater on boron-doped diamond electrode. The same type of electrode was used as a cathode as well. Authors studied the effect of pH and current density on the removal of selected pollutants, including nonylphenol. The efficiency of the treatment was monitored by measuring soluble chemical oxygen demand, UV/Vis spectra (200-900 nm) and by gas chromatography-mass spectrometry preceded by accelerated solvent extraction in combination with solid phase extraction with derivatization. Under optimal conditions of pH 3 and current density 40 mA/cm 2 , 89% of nonylphenol was removed in 1 h. However, some difficulties were encountered because the gas generation caused phase separation, i.e. flotation of solids, but these were overcome by improved mixing [START_REF] Barrios | Electrooxidation treatment for removal of emerging pollutants in wastewater sludge[END_REF].

The same research group further studied the electrooxidation of sludge in a total recirculation mode at 2.8 L/min in a Diacell® reactor with boron-doped diamond electrodes [START_REF] Barrios | Influence of solids on the removal of emerging pollutants in electrooxidation of municipal sludge with boron-doped diamond electrodes[END_REF]. The focus of the research was on the reduction of organic matter in the sludge, measured as volatile solids and chemical oxygen demand. Authors also followed the removal of specific pollutants, among them nonylphenol isomers. Accelerated solvent extraction was performed, followed by solidphase extraction, derivatization and gas chromatographic-mass spectrometric analysis. Other pollutants of interest were bisphenol A and triclosan. After 3 h of treatment, the achieved removal of nonylphenol isomers was 69% and it was the highest compared to other pollutants.

A coupled ozonation-electrooxidation treatment was employed for the treatment of wastewater sludge by the same research group (de Leon-Condes et al. 2017) for the removal of nonylphenol, bisphenol A, and triclosan. They optimized each process separately and then combined them to obtain the one most efficient at pollutant removal. For the electrooxidation, a batch electrochemical reactor with two borondoped diamond anodes was used. The optimized parameters were the current density and pH of solution. In the combined process, ozone was generated and bubbled into solution. To evaluate the efficiency of pollutant degradation, soluble chemical oxygen demand was measured and UV/Vis spectra recorded. Additionally, accelerated solvent extraction of the sludge was performed, followed by gas chromatographic-mass spectrometric analysis. Although the best conditions for both processes were somewhat contradictory, the final conditions selected for the combined process were such as to achieve the best oxidation power, i.e. pH 7.5 and current density 20 mA/cm 2 . With these, the soluble chemical oxygen demand was decreased by 62% and nonylphenol removal was 68%. No degradation products were monitored, however (de [START_REF] De Leon-Condes | A coupled ozonation-electrooxidation treatment for removal of bisphenol A, nonylphenol and triclosan from wastewater sludge[END_REF].

Electrooxidation can be combined with other processes as well. A combination of ozone treatment and electrochemical oxidation was studied by [START_REF] Barrera-Díaz | Integrated advanced oxidation process, ozonation-electrodegradation treatments, for nonylphenol removal in batch and continuous reactor[END_REF] as a means to remove nonylphenol from wastewater and was compared to electrochemical oxidation alone or ozone treatment alone or other advanced oxidation processes. To monitor the removal of the pollutant, chemical oxygen demand, total organic carbon, and absorbance spectra in the 200-600 nm range were measured. Electrochemical oxidation was performed in a batch mode with boron-doped diamond anode and stainless steel cathode, both with a surface area of 25 cm 2 , or in a continuous mode (DiaClean® cell, same electrodes as in batch mode, but with area 70 cm 2 and flow rate 12.6 L/min). The solution was composed of 0.05 M or 0.1 M H 2 SO 4 and 50 mg/L of nonylphenol. The pH was adjusted to 3, 5, and 7 by addition of NaOH solution. Effect of solution pH and current density was studied and the optimal conditions were found to be 3 and 30 mA/cm 2 , respectively. However, ozone treatment was more effective at pH 7 due to formation of hydroxyl radicals which are stronger oxidants than ozone. While after 1 h of combined treatment, 70% of the pollutant was removed, the same time of treatment with ozone alone removed only 30% of pollutant, and electrochemical treatment alone achieved the same removal success after 2 h. [START_REF] Barrera-Díaz | Integrated advanced oxidation process, ozonation-electrodegradation treatments, for nonylphenol removal in batch and continuous reactor[END_REF] calculated the operational costs of the combined treatment as well and compared it to the data for UV/ ozone treatment from the literature. They concluded that due to lower cost, the proposed system was an attractive alternative for the treatment of persistent pollutants in wastewater.

Among the novel electrochemical advanced oxidation processes, electro-Fenton is quite popular for degradation of different pollutants in wastewater. However, only one paper was found for the treatment of alkylphenols and their ethoxylates. [START_REF] Oturan | Occurrence and removal of organic micropollutants in landfill leachates treated by electrochemical advanced oxidation processes[END_REF] tested the electro-Fenton process and electrooxidation for the removal of 55 different pollutants with low degradability, among them 7 alkylphenols and their ethoxylates, from mature landfill leachates (>10 years old). Electro-Fenton was performed using a Pt or a boron-doped diamond anode and a carbon felt cathode. Na 2 SO 4 and 0.2 mM Fe 2+ were added to the landfill leachate that was saturated with O 2 , with the pH set to 3. At a constant current of 500 or 1000 mA, H 2 O 2 was produced in situ from the dissolved oxygen. The electrooxidation process was conducted with a boron-doped diamond anode and a carbon felt cathode in a landfill leachate with or without added Na 2 SO 4 and without pH adjustment. The same currents as in electro-Fenton were applied. The overall performance of both processes for the removal of contaminants was followed by dissolved total organic carbon measurement. Specific analyses were also performed for each group of pollutants. For alkylphenols and their ethoxylates, solid-phase microextraction in combination with gas chromatography-mass spectrometry or solid-phase extraction followed by ultrahigh-performance liquid chromatography-tandem mass spectrometry was applied. An electro-Fenton on a boron-doped diamond electrode removed 87-93% of total organic carbon in 18 h of operation, compared to a Pt electrode that removed 71-78%. The reason was most probably the better availability of physisorbed hydroxyl radicals on the boron-doped diamond electrode, while they were chemisorbed on the Pt electrode. Increasing the current from 500 mA to 1000 mA increased the removal of pollutants, but significantly less than would be expected because the parasitic reactions on the electrode were increased as well. The same was true for electrooxidation on the boron-doped diamond anode: by increasing the current, the removal was enhanced by only around 6%, showing that the efficiency of the current was higher at lower current density. Overall, both electrochemical processes were very efficient for the removal of the specific pollutants. For alkylphenols and their ethoxylates, the removal was 85-100% by electrooxidation and 96-100% by electro-Fenton. Therefore, both processes can be used to successfully treat complex mature landfill leachates containing several recalcitrant pollutants [START_REF] Oturan | Occurrence and removal of organic micropollutants in landfill leachates treated by electrochemical advanced oxidation processes[END_REF].

Photoelectrooxidation is a combined electrochemical and photolytic treatment yielding good results with different emerging contaminants. da Silva et al. (2015a) applied it for the treatment of nonylphenol ethoxylate. The electrochemical cell contained a concentrical dimensionally stable Ti/Ru 0.3 Ti 0.7 O 2 anode and a Ti/TiO 2 cathode around the high-pressure commercial mercury vapor lamp (principal emission band at 254 nm). Authors optimized several parameters: lamps of different voltage, current density, and treatment time. The removal of the pollutant was monitored by UV/Vis spectrometry, total organic carbon measurement, gas chromatography-mass spectrometry, and ecotoxicity assay. The maximal removal in a Na 2 SO 4 solution (supporting electrolyte) was obtained with a 250 W lamp, current density 10 mA/cm 2 , and 4 h of treatment. Under these conditions, 83% of the pollutant was mineralized as evidenced by total organic carbon measurement and reduced toxicity. With the weaker lamp (125 W), what formed was mainly nonylphenol which is even more problematic than the parent compound. Based on the gas chromatographic-mass spectrometric analysis, authors were able to propose the degradation pathway with the intermediates alkylphenol and alkyl-alcohol, further mineralized to CO 2 and water (da Silva et al. 2015a).

The same research group published another paper where they compared direct photolysis, heterogeneous photocatalysis, electrochemical oxidation, and photoassisted electrochemical oxidation for the removal of nonylphenol ethoxylate from synthetic wastewater, containing the commercial degreasing product ULTRANEX NP40® and Na 2 SO 4 as a supporting electrolyte (da Silva et al. 2015b). In both electrochemical processes, the same electrodes were used: a dimensionally stable Ti/ Ru 0.3 Ti 0.7 O 2 anode and a Ti/TiO 2 cathode. All treatments were performed for 4 h and the removal was assessed by UV/Vis spectrometry, total organic carbon measurement, gas chromatography-mass spectrometry, and phytotoxicity assay (Lactuca sativa and Allium cepa seeds as test organisms). The highest removal and mineralization up to 83% was achieved with the photo-assisted electrochemical oxidation system described in their previous paper (da Silva et al. 2015a). Phytotoxicity assays didn't show any change in toxicity compared to non-treated samples, except for samples treated by photo-assisted electrochemical oxidation with a lamp of lower intensity (125 W), where nonylphenol was produced as a stable intermediate and the toxicity to Lactuca was actually increased. The optimal process was also economically feasible as shown by the cost analysis (da Silva et al. 2015b).

Among the novel electrochemical advanced oxidation processes, photoelectrocatalysis is a combination of photolytic degradation and electrochemical catalysis. [START_REF] Fan | Application of carbon aerogel electrosorption for enhanced Bi 2 WO 6 photoelectrocatalysis and elimination of trace nonylphenol[END_REF] applied photoelectrocatalysis and electrosorption to degrade trace concentrations of nonylphenol. They synthesized three types of electrodes: carbon aerogel, Bi 2 WO 6 on carbon aerogel, and Bi 2 WO 6 on F-doped SnO 2 . These electrodes were used as working electrodes in a three-electrode cell containing Na 2 SO 4 as a supporting electrolyte. Nonylphenol concentration in a solution or on an electrode was monitored by solvent extraction, followed by high-performance liquid chromatography with UV detection. Firstly, electrosorption parameters were studied. The key parameters were found to be the potential of the working electrode and the pH of solution, due to the weakly acidic nature of nonylphenol (pK a 10.7). Best adsorption was achieved at potentials around +0.6 V (vs. saturated calomel electrode) and alkaline pH > 12. Adsorption fitted well to the pseudo-first-order kinetics model for Bi 2 WO 6 /F-doped SnO 2 , and to the pseudo-second-order model for carbon aerogel and Bi 2 WO 6 /carbon aerogel. Maximal adsorption capacity of the latter electrode under optimal conditions was 920 μg/L while the other two electrodes performed less well. Next, photocatalytic and photoelectrocatalytic processes under simulated sunlight were compared for nonylphenol degradation. Bi 2 WO 6 material absorbs visible light at 426 nm, but carbon aerogel presence decreases the absorption. Nevertheless, photoelectrocatalysis on the Bi 2 WO 6 /carbon aerogel electrode was the most efficient and was further applied on real wastewater mixed with a nonylphenol solution. Despite the competition for adsorption by matrix components, the electrode retained good performance and reduced the concentration of nonylphenol from 1 mg/L to 6.4 μg/L after 8 h of photoelectrocatalysis. Total organic carbon was reduced by 66.1%. Moreover, the electrode showed good selfcleaning properties [START_REF] Fan | Application of carbon aerogel electrosorption for enhanced Bi 2 WO 6 photoelectrocatalysis and elimination of trace nonylphenol[END_REF].

The same research group synthesized two other novel electrodes, namely a {0 0 1}-TiO 2 electrode and the same electrode decorated with hydrophobic perfluoroalkyl groups -a D-{0 0 1}-TiO 2 electrode [START_REF] Fan | Adsorption driven preferential degradation of alkyl phenols on hydrophobic perfluoroalkyl modified-TiO 2[END_REF]). Both were used in a threeelectrode system as working electrodes with a Pt counter electrode, a saturated calomel reference electrode, and Na 2 SO 4 as a supporting electrolyte. The working electrode was irradiated by a xenon lamp (300 mW/cm 2 ). The experiments were performed in alkyl phenol (octyl, nonyl, and heptyl) solutions, the removal of which was monitored by high-performance liquid chromatography with UV detection. The optimal potential of the working electrode was +0.6 V. [START_REF] Fan | Adsorption driven preferential degradation of alkyl phenols on hydrophobic perfluoroalkyl modified-TiO 2[END_REF] tested static adsorption of pollutants on the electrode for 2 h, and in a separate experiment, photoelectrocatalytic degradation for 5 h. The perfluoroalkyl-decorated electrode showed approximately twice higher adsorption due to matching polarity with the pollutants, which was confirmed by infrared spectroscopy. Similarly, the developed photocatalytic current upon irradiation was up to twice higher compared to a bare electrode. These results showed the possibility of selective degradation of specific pollutants in the wastewater treatment.

Similarly, [START_REF] Xin | Photodegradation performance and mechanism of 4-nonylphenol by WO 3 /TiO 2 and TiO 2 nanotube array photoelectrodes[END_REF] prepared WO 3 /TiO 2 and TiO 2 nanotube array photoelectrodes and applied them for either photocatalytic or photoelectrocatalytic degradation of 4-nonylphenol. The experiments were performed in an electrochemical cell with one of the prepared electrodes as the anode and a Pt foil cathode. The anode was irradiated with a xenon lamp (400-650 nm). The removal of the pollutant was monitored by high-performance liquid chromatographic analysis. Besides, the hydroxyl radical concentration was determined by means of formation of a fluorescent product. In addition to the type of electrode, the effect of pH and the presence of inorganic anions (SO 4 2-, Cl -, HCO 3 -, and NO 3 -) was studied. After 2 h of photoelectrocatalytic process, the degradation of nonylphenol was 80.1% and 92.3% with a TiO 2 or a WO 3 /TiO 2 photoelectrode, respectively, and was higher for both electrodes than with photocatalysis or electrocatalysis alone. The WO 3 /TiO 2 photoelectrode had a better performance because of lower band gap of WO 3 , leading to a higher production of hydroxyl radicals. The effect of pH was twofold: firstly, acidic or alkaline pH promoted the formation of hydroxyl radical better than in the neutral solution, but on the other hand, the actual degradation of the pollutant was the highest at neutral pH. The authors explained this behavior by decreased adsorption of the pollutant on the electrode at alkaline pH due to coulombic repulsion, while at the acidic pH, excess oxonium ions hindered the degradation. Finally, the effect of commonly present anions (SO 4 2-, Cl -, HCO 3 -, and NO 3 -) was studied. All four anions inhibited the degradation of nonylphenol to various degrees. The inhibition was more pronounced on the TiO 2 photoelectrode, except for NO 3 -, which showed a greater negative effect on the WO 3 /TiO 2 photoelectrode. [START_REF] Xin | Photodegradation performance and mechanism of 4-nonylphenol by WO 3 /TiO 2 and TiO 2 nanotube array photoelectrodes[END_REF] identified different reasons for the inhibitory effect of anions, among them hydroxyl radical scavenging, adsorption on the photoelectrode, formation of new radical species with lower activity, etc. In spite of promising results, these findings limit the use of fabricated electrodes in real wastewater.

Electrochemical approaches can be combined also with other established treatment options for the removal of pollutants from wastewater. The adsorption of nonylphenol on multi-walled carbon nanotubes was studied in a Na 2 SO 4 electrolyte without applying electricity, with electrochemical assistance under open circuit conditions, and at different polarization potentials (Li et al. 2014b). For the latter, a three-electrode system consisting of a carbon nanotubes working electrode, a Pt counter electrode, and a saturated calomel reference electrode was used to apply working electrode potentials of 0.6 V, 0.3 V, -0.3 V, and -0.6 V. The concentration of the pollutant was determined by high-performance liquid chromatography with fluorescence detection. The best results were achieved at a potential of -0.6 V with 7.9-fold increase in adsorption rate and 1.7-fold increase in adsorption capacity compared to adsorption without electrochemical assistance. Adsorption kinetics were fitted to several different models, while the isotherms were fitted to the Langmuir and Freundlich models. The former showed better correlation and fit with the experimental data (Li et al. 2014b).

Nonylphenol can be removed from the wastewater by a wide variety of approaches as evidenced in this chapter. One of the possible removal methods is adsorption on carbon nanotubes. The electrokinetic regeneration of carbon nanotubes saturated with nonylphenol was studied by [START_REF] Yuan | Regeneration of spent carbon nanotube by electrokinetic process with binary metallic oxide electrodes of MnO 2 /Ti RuO 2 /Ti, and PbO 2 /Ti[END_REF]. Carbon nanotube layers and Ottawa sand layers were placed in the middle compartment between the anode and cathode compartments. Different electrodes, commercial or made by authors, were tested as anodes: carbon, titanium, and three binary metallic electrodes (MnO 2 /Ti, RuO 2 /Ti, and PbO 2 /Ti). The cathode was made of stainless steel. Different processing fluids were tested as well: de-ionized water, citric acid, NaOH, and NaCl. The treatment proceeded at 2 V/cm for 8 h. The concentration of nonylphenol in different compartments was determined (by high-performance liquid chromatography), as well as pH, electric current, and electroosmotic flow. The degradation of nonylphenol was the most efficient (38.4-69.0% by different electrodes) in NaCl, presumably because of the formation of hydroxyl radicals and hypochlorite ions compared to other fluids where only hydroxyl radicals were formed. Of the tested electrodes, the RuO 2 /Ti electrode was the most efficient for nonylphenol removal (69.0%). The principal mechanism was the electromigration of the pollutant into the anode compartment and its subsequent electrooxidation [START_REF] Yuan | Regeneration of spent carbon nanotube by electrokinetic process with binary metallic oxide electrodes of MnO 2 /Ti RuO 2 /Ti, and PbO 2 /Ti[END_REF]. The same research group published very similar study on electrokinetic regeneration of carbon nanotubes saturated with nonylphenol [START_REF] Yuan | Regeneration performance of carbon nanotube by binary metallic oxide electrodes electrokinetic system[END_REF]. The design of the experiment was very similar as in their previous paper [START_REF] Yuan | Regeneration of spent carbon nanotube by electrokinetic process with binary metallic oxide electrodes of MnO 2 /Ti RuO 2 /Ti, and PbO 2 /Ti[END_REF], except for some new binary metallic oxide electrodes. Namely, they tested the following anodes: carbon, PbO 2 /Ti, PbO 2 -Co/Ti, and PbO 2 -SnO 2 + Sb 2 O 3 /Ti. The same electrokinetic set-up and the same processing fluids were used as in their previous experiment. They achieved the highest removal of nonylphenol in a system with NaCl processing fluid and a PbO 2 -Co/Ti electrode, namely 71.4-80.0%, which was better than with electrodes studied in their previous paper [START_REF] Yuan | Regeneration of spent carbon nanotube by electrokinetic process with binary metallic oxide electrodes of MnO 2 /Ti RuO 2 /Ti, and PbO 2 /Ti[END_REF].

Coming from the same research group, [START_REF] Dai | Regeneration of spent carbon nanotubes by electrochemical oxidation over RuO 2 /Ti electrode[END_REF] studied the possibility of regeneration of carbon nanotubes with adsorbed nonylphenol by electrochemical oxidation. The electrochemical cell consisted of an anode (different materials listed below) and a stainless steel cathode, while the carbon nanotubes with adsorbed nonylphenol were placed between the electrodes, with their migration restricted by filters. Different parameters were optimized. Three anode materials were tested: carbon, titanium, and RuO 2 /Ti. Different electrolytes were studied as well: citric acid, NaOH, and NaCl. Voltage and time of treatment were also studied. The concentration of nonylphenol in the cell was monitored by high-performance liquid chromatography with UV detection. The best removal efficiency was achieved in NaCl on a homemade RuO 2 /Ti electrode, namely 69%. The main degradation mechanisms were established to be electroosmotic migration, followed by anodic oxidation. The species responsible for degradation were found to be hydroxyl radical and hypochlorite ion in NaCl solution, while in the other two electrolytes, only the former were active. Nonylphenol was mineralized to CO 2 and water. Regenerated carbon nanotubes maintained 96.2% of their initial adsorption capacity. [START_REF] Dai | Regeneration of spent carbon nanotubes by electrochemical oxidation over RuO 2 /Ti electrode[END_REF] also provided a cost estimation by taking into account the electrode cost, as well as power and electrolyte consumption. They concluded that the estimated cost was lower than that of the comparable approaches in the literature.

Electrochemical treatment options are applied to other samples besides wastewater and similar but even more complex landfill leachate. A similar approach as for the regeneration of carbon nanotubes can be applied for direct removal of pollutants from contaminated soil. It is called electrokinetic treatment and removes pollutants by applying low direct current, causing their electroosmosis, electromigration, and electrophoresis. [START_REF] Guedes | Electrokinetic remediation of six emerging organic contaminants from soil[END_REF] applied electrokinetic treatment to remove six emerging contaminants, among them nonylphenol and octylphenol, from three types of soil. The concentration of target compounds was determined by highperformance liquid chromatography with diode-array detection preceded by solvent extraction. Experiments were performed in an electrochemical cell with two electrode compartments with platinized titanium electrodes. Soil saturated with deionized water was placed between them and separated by cellulose filters. The electrolyte was a NaNO 3 solution, which was percolated through compartments by a peristaltic pump. Under galvanostatic conditions, hydroxyl radicals were produced, capable of degrading pollutants. Authors studied the effect of applied current, electroosmotic flow and permeability of different soils, as well as the volume and pH in the anode and cathode compartments. The final percentage of remaining pollutants was statistically similar for different treatments and ranged between 17-50% or 27-48% for two different soils. Octylphenol was better degraded than nonylphenol, probably because of lower water solubility and lower mobility of the latter. Pollutants reaching the electrodes were presumably degraded, but the transformation products were not studied [START_REF] Guedes | Electrokinetic remediation of six emerging organic contaminants from soil[END_REF].

In a study by [START_REF] Hung | Effect of processing fluid and initial concentration on electrokinetic removal of environmental hormone-nonylphenol (NP) from soil matrix[END_REF], nonylphenol was removed from soil by an electrokinetic process. The effect of the following parameters was studied: processing fluid (de-ionized water, citric acid, NaOH, and methanol) and current density. The concentration of the pollutant was monitored in the soil and both electrode compartments, using high-performance liquid chromatography with UV detection. The best removal was achieved in methanol, i.e. 53-69% after 5 days at 1 V/cm. Most of the pollutant (88.8-94.2%) was found in the cathode compartment after the treatment, leading to the conclusion that the predominant process of nonylphenol removal from the soil was electroosmosis rather than electromigration.

To summarize, electrochemical advanced oxidation processes are a viable option for the removal of alkylphenols and their ethoxylates from wastewater, landfill leachate, and even solid environmental samples such as the soil. Electroxidation alone or in combination with chemical or photolytic treatment is the most popular approach, which is effective, fast, and cost-efficient. The main shortcoming of the reviewed studies, however, is the lack of thorough analysis of the transformation products. Only too frequently it is simply assumed that the pollutants are mineralized during treatment, based on total organic carbon measurements.

Photocatalyst Nanoparticles for Degradation of Alkylphenol Polyethoxylates

Among the advanced oxidation processes used in water and wastewater treatment, photocatalysis, as a green chemical pathway, plays an important role as it is capable of degrading and mineralizing contaminants such as dyes, phenols and pesticides into harmless products under mild conditions [START_REF] Ike | Degradation of biotansformation products of nonylphenol ethoxylates by ozonation and UV/TiO 2 treatment[END_REF][START_REF] Oh | Photocatalytic degradation of organic contaminants in water[END_REF][START_REF] Wang | Photodegradation of nonylphenol polyethoxylates in aqueous solution[END_REF][START_REF] De La Fuente | Degradation of nonylphenol ethoxylate-9 (NPE-9) by photochemical advanced oxidation technologies[END_REF][START_REF] Ameta | Photocatalytic degradation of organic pollutants: a review[END_REF][START_REF] Rammohan | Green photocatalysis for degradation of organic contaminants: a review[END_REF][START_REF] Umar | Photocatalytic of organic pollutants in water[END_REF][START_REF] Pirilä | Photocatalytic degradation of organic pollutants in wastewater[END_REF][START_REF] Liang | Photocatalytic degradation of nonylphenol ethoxylate and its degradation mechanism[END_REF]. This process involves chemical reactions that take place in the presence of light and a photocatalyst. A photocatalyst such as titanium dioxide is a semiconductor, which increases the rate of reaction by its presence. Titanium dioxide (TiO 2 ) has been widely used not only in environmental chemistry but also in energy domain and other applications such as sanitation and anti-fog coatings because of its high photoactivity, high stability, low cost, non-toxicity (safety to the environment and humans). TiO 2 -based photocatalysis is known to be one of the most promising avenues for water purification and wastewater treatment. However, the cost of using UV radiation (titania is activated in the UV range due to its wide band gap energy) still prevents its widespread application. Work is therefore proposed to reduce the energy bandgap of titanium dioxide, so as to promote visible activation.

Over the past two decades, numerous studies demonstrated that heterostructured photocatalysts have shown higher photocatalytic activity, compared to individual photocatalysts, in mineralizing harmful organic substances in water [START_REF] Hojamberdiev | Templatefree synthesis of polymer-derived mesophorous SiOC/TiO 2 and SiOc/N-doped TiO 2 ceramic composites for application in the removal of organic dyes from contaminated water[END_REF][START_REF] Ibhadon | Heterogeneous photocatalysis: recent advances and applications[END_REF][START_REF] Wang | Visible light driven type II heterostructures and their enhanced photocatalysis properties: a review[END_REF][START_REF] Dong | Recent developments in heterogeneous photocatalytic water treatment using visible light-responsive photocatalysts: a review[END_REF][START_REF] Liang | Photocatalytic degradation of nonylphenol ethoxylate and its degradation mechanism[END_REF]. In particular, heterostructured photocatalysts based on titanium dioxide, such as ZrO 2 /TiO 2 , ZnO/TiO 2 , CdS/TiO 2 , etc. have attracted a great deal of interest due to their higher charge separation efficiency and their UV-visible light photocatalytic activity [START_REF] Xu | Investigation on mechanism of photocatalytic activity enhancement of nanometer cerium-doped titania[END_REF][START_REF] Chen | Preparation and enhanced photoelectrochemical performance of coupled bicomponent ZnO-TiO 2 nanocomposites[END_REF][START_REF] Gao | An efficient method to form heterojunction CdS/TiO 2 photoelectrodes using highly ordered TiO 2 nanotube array films[END_REF]). The applications of this research concern not only the environmental field but also photoelectrochemical processes and clean energy production [START_REF] Tsuji | Photocatalytic H 2 evolution reaction from aqueous solutions over band structure-controlled (AgIn) x Zn 2(1-x) S 2 solid solution photocatalysts with visible-light response and their surface nanostructure[END_REF]Kim et al. 2005a;[START_REF] Hasegawa | Hierarchically porous monoliths based on N-doped reduced titanium oxides and their electric and electrochemical properties[END_REF].

The adsorption of anionic, cationic and non-ionic surfactants on fly ash carbon (used as an additive in concrete mix to remove surfactants) has been found to be affected by oxidation of the carbon surface [START_REF] Mckay | Use of adsorbents for the removal of pollutants from wastewaters[END_REF]. This study showed that oxidation of the carbon surface in air or by ozone suppresses surfactant adsorption, suggesting that surfactant adsorption occurs primarily on the non-polar surface of the carbon, where adsorption is driven by hydrophobic interaction (i.e. the hydrocarbon chain of the surfactant molecule interacts with the carbon surface). In the analysis of the adsorption of a commercial non-ionic surfactant (Triton™ X-100) from an aqueous solution by carbons, González-Carcía et al. ( 2001) observed that at very low coverage, the adsorption was highly exothermic, corresponding to adsorption in the narrowest pores. The authors suggested that after this initial phase, the exothermic adsorption of the surfactant continued, but at less energetic adsorption sites, and that a second interaction begins to occur: the lateral interaction between the hydrocarbon chains of the already adsorbed molecules. This interaction was considered endothermic for the carbons with the lowest amount of porous structure, i.e. the carbon blacks studied. As the coverage increases this endothermic effect became more dominant and an endothermic plateau was observed in the differential enthalpy at coverage of greater than 0.6 [START_REF] González-Carcía | Influence of porosity on the adsorption enthalpies of a non-ionic surfactant onto carbonaceous materials[END_REF]Loureiro and Kartel 2006). As with the study of adsorbents, the photocatalytic degradation of phenol has received more attention than many chemical species. The reasons for using the phenol molecule are much the same for the study of adsorbents and photocatalysts. Phenol molecules have a good water solubility, are easily detectable by a number of different techniques (UV absorption, high performance liquid chromatography, etc.) and phenol is the parent structure for a number of common organic pollutants, such as chlorophenols, bisphenol A, cresols, nitrophenols, and alkylphenols [START_REF] Mao | TiO 2 photocatalytic purification and treatment of water and air[END_REF]).

Serpone's group has studied the photocatalytic degradation of ionic and nonionic surfactants such as sodium dodecylbenzenesulfonate and benzyldodecyldimethyl-ammonium chloride [START_REF] Serpone | Photocatalysis. Fundamentals and applications[END_REF][START_REF] Hidaka | Photodegradation of surfactants: part VI. Complete photocatalytic degradation of anionic cationic and nonionic surfactants in aqueous semiconductor dispersions[END_REF][START_REF] Pelizzetti | Photocatalytic purification and treatment of water and air[END_REF][START_REF] Zhao | Photodegradation of surfactants. 11. Zeta-potential measurements in the photocatalytic oxidation of surfactants in aqueous titania dispersions[END_REF][START_REF] Serpone | Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates[END_REF]. Their work indicated that there was a relationship between the initial rate of photo-oxidation and the structure of the surfactant [START_REF] Serpone | Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates[END_REF]. Degradation of non-ionic surfactants was also somewhat slower than that of cationic and anionic surfactant. In summary, all the major surfactant types (anionic, cationic and non-ionic) had at least one example member that showed complete photocatalytic conversion or even complete mineralization. Degradation of long hydrocarbon chains within surfactant molecules appeared to occur only slowly, if at all. However, it is important to note that the degradation of the initial surfactant was found to rapidly destroy the surface activity.

Photocatalytic degradation of nonylphenol ethoxylates such as nonylphenol pentaethoxylate using titanium dioxide as the photocatalyst has received some attention in the past [START_REF] Pelizzetti | Photocatalytic degradation of nonylphenol ethoxylated surfactants[END_REF][START_REF] Zhao | Photodegradation of surfactants. 11. Zeta-potential measurements in the photocatalytic oxidation of surfactants in aqueous titania dispersions[END_REF][START_REF] Sherrard | Spectroscopic analysis of heterogeneous photocatalysis products of nonylphenol-and primary alcohol ethoxylate nonionic surfactants[END_REF]. Oxidation of the ethoxylate chain has been attributed generally as a primary degradation pathway for nonylphenol ethoxylates. Serpone and co-workers proposed a model in which oxidation of the aromatic ring and ethoxylate chains were competitive [START_REF] Serpone | Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates[END_REF]. The degradation pathways are initiated by the attack of hydroxyl radicals on the ethoxylate chain and the benzene ring with preferential attack on the longer ethoxylate chains. This was demonstrated by the comparative photodegradation of nonylphenol ethoxylates with different initial ethoxylate chain lengths [START_REF] Hidaka | Photodegradation of surfactants: part VI. Complete photocatalytic degradation of anionic cationic and nonionic surfactants in aqueous semiconductor dispersions[END_REF]. Further oxidation also involves the aliphatic chain, resulting in intermediate products as ethylene glycols and various acidic compounds, and finally a near quantitative conversion to CO 2 [START_REF] Serpone | Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates[END_REF]. [START_REF] Sherrard | Spectroscopic analysis of heterogeneous photocatalysis products of nonylphenol-and primary alcohol ethoxylate nonionic surfactants[END_REF] observed that the degradation of nonylphenol pentaethoxylate occurred preferentially with cleavage of the ethoxylate chain producing short-chain alkylphenol ethoxylates of low solubility. After an initial induction period, cleavage of aromatic rings became an increasingly important route of decomposition. Shortchain nonylphenol pentaethoxylates have also been observed to be persistent and adhere to the surface of titanium dioxide, i.e. they are not observed in free solution, but are observed when extracted from the surface of titanium dioxide using an organic solvent. In all the studies mentioned, complete removal of the non-ionic surfactant is observed with an adequate irradiation time.

To prepare and characterize titanium dioxide -based nanocomposites for use in removing phenol and alkylphenol ethoxylates from wastewater, TiO 2 /C and TiO 2 / SiO 2 nanocomposites have been prepared and a wide range of characterization techniques have been used to define the physical and chemical properties of these composites. Nanostructured composites were evaluated for the adsorption and photocatalytic decomposition of phenolic endocrine disruptors. Two methods were used for the preparation of titania-coated carbon particles, TiO 2 /C. The first used sol-gel chemistry by hydrolysis of titanium isopropoxide for coating spherical activated carbon particles [START_REF] Brinker | Sol-gel science: the physics and chemistry of sol-gel processing[END_REF]. The second involved the hydrolysis of the titanium isopropoxide to take place after the carbon has been in contact with the reagent solution. The first method of contacting the carbon spheres with a pre-formed TiO x gel is capable of giving a high TiO 2 charge on the outer surface of the spheres, while the second method gives a lower charge, which can result in a more uniform and also more stable coating for application in the field of water treatment.

Polyethylene glycols are synthetic polyethers with multifunctional properties, available in a range of molecular weights, used as non-ionic surfactants, e.g. in the formulation of cosmetic and medical products. [START_REF] Sermon | Tuning X/(TiO 2 ) x -(SiO 2 ) 100 -x (0 < x < 40) xerogel photocatalysts[END_REF] investigated the use low-molecular weight polyethylene glycol (PEG 400) as a template for the synthesis of the nanostructured silica-titania matrix. The synthesis of mesoporous silica and titanium oxide was carried out using tetraethoxysilane and titanium alkoxide precursors, NH 4 OH and HCl as catalysts in the presence of PEG 400 as the template or structure-directing compound. The removal of the templates by solvent extraction and calcination has resulted in mesoporous silica-titania materials.

The photocatalytic degradation of two commercial alkylphenol ethoxylates, IGEPAL® CO-520 (a nonylphenol ethoxylate with 5 moles of ethoxylates) and Triton™ X-100 (an octylphenol ethoxylate with 9.5 ethylene oxide units) using PEG-templated TiO 2 and SiO2-TiO 2 has been studied in detail [START_REF] Musaev | Facile synthesis of SiO 2 -TiO 2 photocatalyst nanoparticles for degradation of phenolic water pollutants[END_REF]. The results showed that photodegradation initially occurs by cleavage of the ethoxylate chain and shorter-chain alkylphenol ethoxylates result. Agglomeration of suspended SiO 2 and TiO 2 nanoparticles and their sedimentation was also observed during photodegradation of surfactants. The photocatalytic performance of the combined carbon and titania system follows the same trend as the titania system alone, since the pH is modified. As the pH increases, the photocatalyst performance also increases. It has been found that the performance varies by a factor of 8 in the pH range studied. Therefore, to get the most out of these photocatalyst systems, the pH of solution must be carefully monitored and controlled. The effect of pH on the photocatalytic performance of the TiO 2 /C composites is the same for TiO 2 alone. As with the photodegradation of phenol, the photodegradation of nonylphenol ethoxylates was investigated initially using only the Hg discharge lamp first (Fig. 4.15). The analysis of the results suggests that a by-product/intermediate is formed in the early stages of the reaction and is then degraded by photocatalysis. Following the photocatalytic reaction, the titanium dioxide aggregated and adhered to the walls of the photoreactor. To determine the reason for this aggregation, the titanium dioxide was removed from the reactor and dried overnight at 348 K. The resulting gray paste was ). The results showed that several products of photocatalytic degradation have formed and remained adsorbed on the titanium dioxide surface. Nonylphenol and nonylphenol monoethoxylate which are found in very low concentrations in the aqueous solution are found in great abundance on the surface of TiO 2 . The analysis of the first elution peaks in the chromatogram shows the products of the cleavage of the aromatic ring. These products could not be determined in free solution so, like short-chain, they must be strongly bound to the surface of the titanium dioxide particles.

The main conclusion of this work was that the incorporation of a polymer matrix into the inorganic network, with subsequent formation of a nanoporous structure, increases the efficiency of sol-gel materials during adsorption/photocatalytic purification and separation of various organic pollutants. The composite structure shows molecular selective photocatalysis while the photocatalytic activity of titanium dioxide is non-selective. Although the photocatalytic approach can be applied to remove alkylphenol ethoxylates, many questions remain unanswered. The sedimentation of titanium dioxide particles is a major problem for the application of photocatalysis in the removal of alkylphenol ethoxylates. The use of a stationary support could overcome this problem and ensure that titanium dioxide activity remains high even after prolonged use in the photodegradation of these surfactants. Another possibility for further study arises from the large number of molecules present in the commercial nonylphenol pentaethoxylate and all the intermediates formed during photodegradation. The use of a nonylphenol pentaethoxylate with only one ethoxylate chain length would make it possible to identify the photodegradation intermediates and to more accurately measure the concentration of the nonylphenol pentaethoxylate used.

Zero-Valent Iron-Activated Persulfate Oxidation of Alkylphenol Polyethoxylates

Zero-valent iron, Fe(0,) was originally developed to mitigate chlorinated hydrocarbon industrial solvents disposed in soil and many other toxic species including arsenic in the environment [START_REF] Lackovic | Inorganic arsenic removal by zero-valent iron[END_REF][START_REF] Krishna | A combined treatment approach using Fenton's reagent and zero valent iron for the removal of arsenic from drinking water[END_REF][START_REF] Farrell | Electrochemical and spectroscopic study of arsenate removal from water using zero-valent iron media[END_REF][START_REF] Manning | Arsenic(III) and arsenic(V) reactions with zero valent iron corrosion products[END_REF][START_REF] Kim | Stabilization of available arsenic in highly contaminated mine tailings using iron[END_REF][START_REF] Lien | High-level arsenate removal from groundwater by zero-valent iron[END_REF]. In recent years, significant improvements were made with iron-based technologies and the use of zero-valent iron for the treatment of a variety of other organic contaminants and heavy metals in surface water, groundwater and wastewater has received considerable attention and encouraging results have been reported [START_REF] Bokare | Review of iron-free Fenton-like systems for activating H 2 O 2 in advanced oxidation processes[END_REF][START_REF] Han | Studies on the optimum conditions using acid-washed zero-valent iron/aluminum mixtures in permeable reactive barriers for the removal of different heavy metal ions from wastewater[END_REF][START_REF] Minella | Degradation of ibuprofen and phenol with a Fenton-like process triggered by zero-valent iron (ZVI-Fenton)[END_REF]. The major contaminant groups that have been treated by zero-valent iron materials are industrial dyes, pharmaceuticals, personal care products, explosives, pesticides, heavy metals, surfactants, arsenic and hexavalent chromium. Among the advanced oxidation processes, in particular Fenton, Fenton-like and photo-Fenton processes have gained more attention due to their superior reaction kinetics and treatment efficiencies [START_REF] Safarzadeh-Amiri | The use of iron in advanced oxidation processes[END_REF][START_REF] Nadtochenko | Photolysis of FeOH 2+ and FeCl 2 + in aqueous solution. Photodissociation kinetics and quantum yields[END_REF][START_REF] Arslan-Alaton | Acid dyebath effluent pretreatment using Fenton's reagent: process optimization, reaction kinetics and effects on acute toxicity[END_REF]. Since iron-based advanced oxidation processes are technically and economically attractive compared to other treatment methods, extensive research on treatment applications, reaction pathways and critical process parameters has already been published. However, their common, major drawback is the requirement of a strictly acidic pH (typically between 2 and 5) to enhance iron solubility, and the problem of a solid waste management after treatment (pH re-adjustment) as a consequence of Fe(OH) 3 sludge formation. To overcome these limitations, heterogeneous Fenton-like treatment systems including iron oxides/oxyhydroxides, supported iron salts and more recently zero-valent ironmediated treatment systems have been explored for water and wastewater treatment (Li et al. 2014a;[START_REF] Zhou | Treatment of selected pharmaceuticals by ferrate(VI): performance, kinetic studies and identification of oxidation products[END_REF].

An abundant literature [START_REF] Mueller | Application of nanoscale zero valent iron (nZVI) for groundwater remediation in Europe[END_REF][START_REF] Kharisov | Ironcontaining nanomaterials: synthesis, properties, and environmental applications[END_REF][START_REF] Crane | Nanoscale zero-valent iron: future prospects for an emerging water treatment technology[END_REF][START_REF] Fu | The use of zero-valent iron for groundwater remediation and wastewater treatment: a review[END_REF] in the treatment applications of zero-valent iron and oxidants (mainly peroxides such as hydrogen peroxide) activated by zero-valent iron has recently appeared. In fact, zero-valent iron offers several advantages since it is a very reactive material with a reduction potential of -0.44 V vs. standard hydrogen electrode, relatively non-toxic, abundant, inexpensive, easy to produce and handle [START_REF] Grieger | Environmental benefits and risks of zero-valent iron nanoparticles (n-ZVI) for in-situ remediation: risk mitigation or trade-off?[END_REF][START_REF] Greenlee | Kinetics of zero valent iron nanoparticle oxidation in oxygenated water[END_REF]). The reaction mechanism has been postulated as follows [START_REF] Bremner | Phenol degradation by using hydroxyl radicals generated from zero-valence iron and hydrogen peroxide[END_REF][START_REF] Bergendahl | Fenton's oxidation of MTBE with zero-valent iron[END_REF][START_REF] Fu | The use of zero-valent iron for groundwater remediation and wastewater treatment: a review[END_REF][START_REF] Zhao | Enhanced oxidation of 4-chlorophenol using sulfate radicals generated from zero-valent iron and peroxydisulfate at ambient temperature[END_REF]):

(i). When zero-valent iron undergoes surface oxidation (corrosion), two electrons are transferred from zero-valent iron to dissolved oxygen to produce hydrogen peroxide; (ii). Then, Fe 2+ ions released from the zero-valent iron surface to the reaction bulk react with the in-situ formed hydrogen peroxide and produce HO • and HO 2 • by Fenton and Fenton-like reactions, respectively; (iii). The Fenton and Fenton-like reactions can be enhanced by direct (external) hydrogen peroxide addition to the reaction solution.

The above-listed basic reactions of the zero-valent iron/H + /O 2 treatment system are given in Eqs. 4.1, 4.2, 4.3 and 4.4 (Bergendahl and Thies 2004;[START_REF] Fu | The use of zero-valent iron for groundwater remediation and wastewater treatment: a review[END_REF]. Figure 4.17 shows a schematic illustration of zero-valent iron surface reactions. Zero-valent iron has also been used on supported materials such as carbon, resin, bentonite, kaolinite and zeolites [START_REF] Diao | Use of zero-valent iron nanoparticles in inactivating microbes[END_REF][START_REF] Zhao | Enhanced oxidation of 4-chlorophenol using sulfate radicals generated from zero-valent iron and peroxydisulfate at ambient temperature[END_REF][START_REF] Kusic | Iron-activated persulfate oxidation of an azo dye in model wastewater: influence of iron activator type on process optimization[END_REF] Fig. 4.17 Schematic illustration of zero-valent iron surface reactions 2011; [START_REF] Wang | Effects and mechanism of humic acid on chromium(VI) removal by zero-valent iron (Fe 0 ) nanoparticles[END_REF][START_REF] O'carroll | Nanoscale zero valent iron and bimetallic particles for contaminated site remediation[END_REF][START_REF] Trujillo-Reyes | Supported and unsupported nanomaterials for water and soil remediation: are they a useful solution for worldwide pollution?[END_REF][START_REF] Salam | Removal of nitrate ions from aqueous solution using zero-valent iron nanoparticles supported on high surface area nanographenes[END_REF][START_REF] Mao | Experimental and theoretical aspects of biochar-supported nanoscale zero-valent iron activating H 2 O 2 for ciprofloxacin removal from aqueous solution[END_REF]. In this way oxidation, reduction and adsorption capacities could be improved and aggregation -corrosion problems could be hindered.

Fe

Considering the potential applicability of zero-valent iron treatment technology, some full-scale examples are available including zero-valent iron-based permeable reactive barriers for the in-situ remediation of groundwater that has been designated as a standard treatment technology for contaminated groundwater in 2002 by the US EPA. Peroxydisulfate (S 2 O 8 2-) appears to be an alternative, interesting oxidant to the more classical hydrogen peroxide since it offers several advantages such as high aqueous solubility, high thermal stability, relatively low cost and environmentally acceptable end products such as sulfate [START_REF] Zhao | Enhanced oxidation of 4-chlorophenol using sulfate radicals generated from zero-valent iron and peroxydisulfate at ambient temperature[END_REF][START_REF] Rodriguez | Oxidation of orange G by persulfate activated by Fe(II), Fe(III) and zero valent iron (ZVI)[END_REF]. Sulfate is regulated by water associations and agencies but its toxicity limit is relatively high (>200 mg/L) rendering peroxydisulfate-based treatment processes very promising and ecotoxicologically safe as well. Peroxydisulfate treatment is generally associated with the production of sulfate (SO 4 •-) radicals which are very strong and hence reactive oxidizing agents. SO 4 •-can be generated in different ways; from the activation of persulfate by short UV (UV-C) light, thermally, via power ultrasound and microwave radiation, as well as transition metals and metal oxides. Zerovalent iron activation with peroxydisulfate on the other hand is a relatively cost-effective, efficient and environmentally friendly method and thus has received considerable attention for the removal of emerging contaminants and pollutants [START_REF] Kusic | Iron-activated persulfate oxidation of an azo dye in model wastewater: influence of iron activator type on process optimization[END_REF][START_REF] Xiong | Activating persulfate by Fe 0 coupling with weak magnetic field: performance and mechanism[END_REF][START_REF] Nguyen | Biochar-mediated oxidation of phenol by persulfate activated with zero-valent iron[END_REF]. Zero-valent iron activation not only serves as a slow-releasing source of Fe but also provides a heterogeneous medium for peroxydisulfate activation via direct electron transfer. The mechanism of zero-valent iron-mediated peroxydisulfate treatment involves direct electron transfer from the zero-valent iron or surface-bound Fe 2+ to peroxydisulfate, continuing with a homogenous Fenton-like reaction (Eq. 4.6) that results in SO 4 •- production in the reaction bulk [START_REF] Xu | Degradation of azo dye orange G in aqueous solutions by persulfate with ferrous ion[END_REF]. These reactions are analogous to the hydrogen peroxide activation by zero-valent iron and are shown in Eqs. 4.5 and 4.6. The environmental problem associated with alkylphenol polyethoxylates is the fact that their aerobic/anaerobic transformation products such as nonylphenol and octylphenol [START_REF] Ying | Environmental fate of alkylphenols and alkylphenol ethoxylates -a review[END_REF][START_REF] Ying | Fate, behavior and effects of surfactants and their degradation products in the environment[END_REF]) are usually much more biotoxic and estrogenic than the original surfactants [START_REF] Routledge | Estrogenic activity of surfactants and some of their degradation products assessed using a recombinant yeast screen[END_REF]. Alkylphenol polyethoxylates currently cannot be replaced by alternative surfactants due to technical and economic reasons (Arslan-Alaton and Olmez-Hanci 2012). Consequently, the discharge of nonionic surfactants into industrial and sewage treatment plants as well as the evolution of degradation products in aquatic and terrestrial ecosystems is expected to continue [START_REF] Staples | Ultimate biodegradation of alkylphenol ethoxylate surfactants and their biodegradation intermediates[END_REF].

Fe Fe

Oxidation and electrochemical processes have been proposed for their degradation. Studies related with zero-valent iron-mediated treatment of alkylphenol polyethoxylates are relatively rare. In a relatively recent study, 20 mg/L aqueous Triton™ X-45 which is a commercially important octylphenol polyethoxylate formulation, was subjected to peroxydisulfate oxidation activated with zero-valent iron nanoparticles [START_REF] Temiz | Zero-valent iron-activated persulfate oxidation of a commercial alkyl phenol polyethoxylate[END_REF]. Nano-sized zero-valent iron is one of iron-based nanomaterials with a diameter ranging from 10 to 100 nm. In the first part of this study, zero-valent iron activated peroxydisulfate oxidation of Triton™ was optimized on the basis of pH (pH = 3-9), zero-valent iron (0.5-5 g/L) and peroxydisulfate (0.5-5.0 mM) concentrations by following Triton™ degradation and dissolved organic carbon removal. Poor/inefficient treatment performance (≤15% Triton™ degradation; ≤10% dissolved organic carbon removal) was evident for zero-valent iron treatment in the absence of peroxydisulfate, revealing that peroxydisulfate activation by zero-valent iron is important for effective oxidation of Triton™ and its degradation products. Optimum surfactant treatment conditions were determined as the following: pH = 5, 1 g/L zero-valent iron and 2.5 mM (0.48 g/L) peroxydisulfate. There was no need to carry out Triton™ treatment at pH = 3 since practically equal Triton™ degradation was obtained at pH = 5, which is an environmentally and technically more acceptable pH. The peroxydisulfate/zero-valent iron treatment system was even effective at pH 7, where 80% Triton™ and 30% dissolved organic carbon removal were achieved in 60 min. For selected treatment conditions, 20 mg/L aqueous Triton™ could be degraded in 60 min by >90% accompanied with dissolved organic carbon removal reaching 40%. In addition to Triton™ and dissolved organic carbon abatements, peroxydisulfate consumption and Fe release were also followed during treatment. From the experimental findings it was evident that peroxydisulfate consumption and Fe release followed a parallel trend to Triton™ degradation rates. Acute toxicity bioassays were also conducted to examine the ecotoxicological safety of zero-valent iron/peroxydisulfate treatment system. Acute toxicity profiles decreased significantly from an original inhibition value of 66% and 16% to 21% and practically non-toxic values (< 10%) according to Vibrio fischeri and Pseudokirchneriella subcapitata bioassays, respectively. Apparently, the photobacterium Vibrio fischeri appeared to be more sensitive to the original Triton™ solution and its degradation products than the microalga Pseudokirchneriella subcapitata. In Table 4.8, Triton™ and dissolved organic carbon removal efficiencies obtained for zero-valent iron-mediated peroxydisulfate treatment are summarized for different initial pH values [START_REF] Temiz | Zero-valent iron-activated persulfate oxidation of a commercial alkyl phenol polyethoxylate[END_REF]. It is interesting to note that with zero-valent iron/peroxydisulfate treatment, acceptable and Fenton-comparable Triton™ and dissolved organic carbon removal efficiencies could be achieved even at a neutral pH value. These results demonstrate that iron-based oxidative processes are efficient in terms of treatment performance. Nevertheless, much work is still needed to develop more compact, efficient, affordable, and ecotoxicologically safe processes for the destructive treatment of industrial pollutants.

Catalytic Ozonation of Alkylphenols

Catalytic ozonation, i.e. the combination of a solid catalyst with ozone, is a promising technology for application in water treatment because of its simplicity (oxidation in the ambient temperature and pressure) and efficiency. Catalytic ozonation shows great advantages in removing refractory organics in water. The technique can be used either in homogeneous phase (metal ions as catalyst present in the reaction system) or in heterogeneous phase (catalysts are metal oxide and metal or metal oxide on supports). Many works showed the potential of this process to degrade pharmaceuticals such as diclofenac in water [START_REF] Castro | Evaluation of heterogeneous catalytic ozonation process for diclofenac degradation in solutions synthetically prepared[END_REF]. As already discussed, this method coupled with an activated carbon step is promising in water treatment.

However, there are few literatures on destruction of alkylphenols by catalytic ozonation process. [START_REF] Anandan | Sonochemical synthesis of Bi 2 CuO 4 nanoparticles for catalytic degradation of nonylphenol ethoxylate[END_REF] used Bi 2 CuO 4 nanoparticles catalyst for catalytic ozonation of nonylphenol ethoxylate. This study showed significantly improved destruction of the pollutant as compared to non-catalytic ozonation. [START_REF] Restivo | Catalytic ozonation of organic micropollutants using carbon nanofibers supported on Monoliths[END_REF][START_REF] Restivo | Carbon nanofibers Doped with nitrogen for the continuous catalytic ozonation of organic pollutants[END_REF] showed that both non-catalytic and catalytic ozonation achieved similar degradation degree of nonylphenol while using carbon nanofibers as catalyst in a continuous process. Nonylphenol very quickly reacted with molecular ozone as its aromatic ring is very vulnerable to ozone attack. However, introduction of catalyst improved the extent of mineralization of the pollutant since reactive oxygen species like hydroxyl radicals are less selective. This less selective species is also found to mineralize lower molecular weight recalcitrant compounds such as oxalic acid [START_REF] Wang | Tailored synthesis of active reduced graphene oxides from waste graphite: structural defects and pollutantdependent reactive radicals in aqueous organics decontamination[END_REF]. Though somewhat promising, this catalytic ozonation of alkylphenols is still a developing topic.

Conclusion

Although legislation concerning the use of alkylphenols and their polyethoxylated derivatives, classified as priority substances in terms of monitoring and action, has become increasingly strict in recent years, these molecules are found in the various environmental compartments, especially in the aquatic environment. This is a result of their wide use and their presence in the environment is entirely due to human activity. Alkylphenols and alkylphenol polyethoxylates can end up directly in the environment through industrial effluent or transit through municipal wastewater treatment plants. Existing conventional water and wastewater treatment plants were not designed for these new contaminants. In this context, it is necessary to propose and develop various efficient technologies for the elimination of alkylphenols from water and wastewater that are efficient, economically viable, technologically simple, and without environmental impact. Over the past two decades, alkylphenols have indeed become a relevant research topic for scientists interested in water engineering issues related to their treatment. Using selected examples, this chapter summarizes recent trends in proposed advanced treatment methods for the removal of alkylphenols and alkylphenol polyethoxylates from wastewater. The techniques such as adsorption onto cyclodextrin polymers or molecularly imprinted polymer, biodegradation using algae-based technologies or catalytic ozonation, are still at the pilot test stage. Others, such as ozonation-activated carbon and advanced oxidation treatments, have already been proven at the industrial wastewater scale. Among these technologies cited in this chapter, advanced oxidation processes, in association with biodegradation and/or adsorption, seem to be the technique of the future, although their costs still prevent their widespread use. Indeed, these techniques could be part of the operating scheme of municipal wastewater treatment plants. They could be used either in primary treatment, as a complement to biological methods to help the degradation processes of refractory substances, or in tertiary treatment, as a complement to an adsorption step on activated carbon, to eliminate residual pollution. The latter option seems to be preferred as it can be useful in the context of a more generalized reuse of treated wastewater.

Fig. 4 . 1

 41 Fig. 4.1 General molecular structure for alkylphenols abbreviated APs and alkylphenol polyethoxylates abbreviated APnEOs (NP nonylphenol, OP octylphenol, NPnEO nonylphenol ethoxylates, OPnEO octylphenol ethoxylates)

Fig. 4 . 3

 43 Fig. 4.3 Representation of the inclusion phenomena between a cyclodextrin molecule (the host) and a contaminant (the guest) to form inclusion complexes (K f is a constant of formation)

Fig. 4 . 4

 44 Fig. 4.4 Comparison of the structure of (a) a cross-linked epichlorohydrin cyclodextrin polymer and (b) a cross-linked epichlorohydrin dextran resin (Sephadex®)

Fig. 4 .

 4 Fig. 4.10 Concentration pattern of alkylphenol ethoxylates and related metabolites in the fed sludge and in the digested sludge after the anaerobic and aerobic digestion for the two operating conditions: anaerobic mesophilic-aerobic at T = 20 °C (AA20) and anaerobic mesophilic-aerobic at T = 37 °C (AA37)

Fig. 4 .Fig. 4 .

 44 Fig. 4.13 Removal of chemical oxygen demand in raw industrial wastewater by ozone/granular activated carbon process

Fig. 4 .

 4 Fig. 4.15 Photodegradation of a 1000 ppm aqueous solution of nonylphenol ethoxylate by TiO 2 at pH 7

Fig. 4 .

 4 Fig. 4.16 High performance liquid chromatogram of a nonylphenol pentaethoxylate (NP5EO) solution with UV-irradiated PEG-templated SiO 2 -TiO 2 (time = 90 min, NP4EO nonylphenol tetraethoxylate, NP6EO nonylphenol hexaethoxylate, NP10EO nonylphenol decaethoxylate)

Table 4 . 8

 48 Percent Triton™ and dissolved organic carbon removal obtained for zero-valent ironmediated peroxydisulfate treatment at varying pH values in un-buffered aqueous solution (other experimental conditions: Triton™ concentration 20 mg/L; dissolved organic carbon 14 mg/L; zero-valent iron concentration 1 g/L; peroxydisulfate concentration 0.48 g/L; time 60 min) Initial reaction pH Triton™ removal (%) Dissolved organic carbon removal (

Table 4 .2

 4 Chemical Abstracts Service (CAS) registry names, numbers, abbreviation and properties for several alkylphenols

		b ow logK	4.48																4.17	4.21			4.12
	Water	solubility a	5.43																3.02	3.38			12.6
														15 H 24 O
		Substance Formula	mixture C 15 H 24 O				mixture C 15 H 24 O				one isomer C 15 H 24 O			mixture (C 2 H 4 O) n C					mixture C 17 H 28 O 2	mixture C 19 H 32 O 3	C 17 H 28 O 2	C 19 H 32 O 3	one isomer C 14 H 22 O
		Structure	C 9 H 19 : linear				C 9 H 19 : linear	and/or branched			C 9 H 19 : linear			C 9 H 19 : linear					C 9 H 19 : linear	C 9 H 19 : linear	C 9 H 19 : linear	C 9 H 19 : linear	branched
		Abbreviations	NP	NPs	n-NP		4-NP	p-NP	NP		4-n-NP	n-4-NP	p-NP	4-NPnEOs	4-NPnEO	NPnEOs			NP1EO	NP2EO	n-4-NP1EO	n-4-NP2EO	t-4-OP	4-OP	OP
		CAS Number CA index names	25154-52-3 nonylphenol	nonylphenols	n-nonylphenol	monononyphenol	84852-15-3 4-nonylphenol	branched 4-nonylphenol	para-nonylphenol	p-nonylphenol	104-40-5 4-n-nonylphenol	linear para-nonylphenol	n-para-nonylphenol	26027-38-3 polyethoxylate 4-nonylphenol	nonylphenol ethoxylates	poly(oxy-1,2-ethanediyl),	α-(4-nonylphenyl)-ω-	hydroxynonylphenol	28679-36-3 nonylphenol monethoxylate	27176-93-8 nonylphenol diethoxylate	104-35-8 4-nonylphenol monethoxylate	20427-84-3 4-n-nonylphenol diethoxylate	140-66-9 4-octylphenol	para-octylphenol	octylphenol	4-tert-octylphenol	4-(1,1,3,3-tetramethylbutyl)	phenol

Removal in% sucrose starch maltodextrin cyclodextrin carbon

	Fig. 4.6 Comparison of different materials for the removal (in %) of several alkylphenols (NP:
	nonylphenol, mixture, CAS number 25154-52-3; 4-NP: 4-nonylphenol, mixture, CAS number
	84852-15-3; 4-n-NP: linear para-nonylphenol, CAS number 104-40-5; 4-n-OP: linear para-
	octylphenol, CAS number 1806-26-4; 4-tert-OP: para-octylphenol, CAS number 140-66-9; adsor-
	bent dose 2 g/L; initial concentration 100 μg/L; contact time 4 h; agitation 250 rpm; T 25 °C;
	pH 6; n = 2)

-NP 4-n-OP 4-tert-OP Removal in % 25 g/L 50 g/L 100 g/L

	100
	80
	60
	40
	20
	0 4-nFig. 4.7 Effect of initial alkylphenol concentration on the removal (expressed as % abatement) of NP 4-NP
	five alkylphenols present in a mono-contaminated solution by a cyclodextrin polymer (NP: nonyl-
	phenol, mixture, CAS number 25154-52-3; 4-NP: 4-nonylphenol, mixture, CAS number
	84852-15-3; 4-n-NP: linear para-nonylphenol, CAS number 104-40-5; 4-n-OP: linear para-
	octylphenol, CAS number 1806-26-4; 4-tert-OP: para-octylphenol, CAS number 140-66-9; condi-
	tions: adsorbent dose 2 g/L; contact time 4 h; agitation 250 rpm; T 25 °C; pH 6; n = 2)

0 20 40 60 80 100 NP 4-NP 4-n-NP 4-n-OP 4-tert-OP Removal in % without NaCl with NaCl 0.1 M

	Removal in %
	25 g/L	50 g/L	100 g/L
	Fig. 4.8 Effect of initial alkylphenol concentration on the removal (expressed as % abatement) of
	five alkylphenols present in a mixture by a cyclodextrin polymer (NP: nonylphenol, mixture, CAS
	number 25154-52-3; 4-NP: 4-nonylphenol, mixture, CAS number 84852-15-3; 4-n-NP: linear
	para-nonylphenol, CAS number 104-40-5; 4-n-OP: linear para-octylphenol, CAS number
	1806-26-4; 4-tert-OP: para-octylphenol, CAS number 140-66-9; adsorbent dose 2 g/L; contact
	time 4 h; agitation 250 rpm; concentration 25, 50 or 100 μg/L for each alkylphenol in mixture; T
	25 °C; pH 6; n = 2)
	Fig. 4.9 Effect of NaCl on the removal (expressed as % abatement) of five alkylphenols present
	in solution by a cyclodextrin polymer (NP: nonylphenol, mixture, CAS number 25154-52-3; 4-NP:
	4-nonylphenol, mixture, CAS number 84852-15-3; 4-n-NP: linear para-nonylphenol, CAS number
	104-40-5; 4-n-OP: linear para-octylphenol, CAS number 1806-26-4; 4-tert-OP: para-octylphenol,
	CAS number 140-66-9; adsorbent dose 2 g/L; contact time 4 h; agitation 250 rpm; concentration
	100 μg/L for each alkylphenol in synthetic solution; T 25 °C; pH 6; n = 1)

Table 4 .3

 4 Concentrations (in μg/L) of alkylphenols present in three industrial effluents before and after sorption on cyclodextrin polymer (NP: nonylphenol, mixture, CAS number 25154-52-3; 4-NP: 4-nonylphenol, mixture, CAS number 84852-15-3; 4-n-NP: linear para-nonylphenol, CAS number 104-40-5; 4-n-OP: linear para-octylphenol, CAS number 1806-26-4; 4-tert-OP: paraoctylphenol, CAS number 140-66-9; adsorbent dose 2 g/L; contact time 4 h; agitation 250 rpm; T 25 °C; pH 6.5; n = 1)

		Effluent 1		Effluent 2		Effluent 3
		Before	After	Before	After	Before	After
	Alkylphenol	treatment	treatment	treatment	treatment	treatment	treatment
	NP	45.9	2.3	120	<0.5	49.2	1.23
	4-NP	<0.5	<0.5	85.2	2.31	26.5	0.78
	4-n-NP	13.5	<0.5	50.3	7.2	<0.5	<0.5
	NP1EO	<0.1	<0.1	<0.1	<0.1	7.11	<0.1
	NP2EO	5.1	<0.1	2.98	<0.1	10.5	1.25
	4-n-OP	12.3	<1	32.1	1.32	5.99	0.99
	4-tert-OP	7.9	<0.5	44.2	4.44	1.23	<0.5
	4-tert-	6.12	1.05	<0.1	<0.1	<0.1	<0.1
	OP1EO
	4-tert-	<0.1	<0.1	<0.1	<0.1	0.99	<0.1
	OP2EO

Table 4

 4

	.4 Characterization	Parameter	Concentration Unit
	of the sludge (values are reported as average value and standard deviations in	Total solids Volatile solids	39.71 (3.47) 27.44 (1.95)	g/L g/L
	parentheses; dw dry weight)	Chemical oxygen demand 39.87 (9.32)	g/L
		Total organic carbon	309.44 (28.51) g/kg dw
		Total N	60.35 (2.14)	g/kg dw
		Total P	19.01 (5.36)	g/kg dw
		Total S	10.48 (2.74)	g/kg dw

Table 4 .5

 4 Range of concentration in μg/kg dw of the analysed alkylphenol ethoxylates and related metabolites, abbreviation (LOD limit of detection in μg/kg dw ; dw dry weight)

	Alkylphenol ethoxylates and related metabolites	Abbreviation	LOD	Concentration
	4-tert-octylphenol monoethoxylate	OP1EO	1.86	24-2280
	4-tert-octylphenol diethoxylate	OP2EO	0.75	6-11
	Nonylphenol monoethoxylate	NP1EO	0.75	197-312
	Nonylphenol diethoxylate	NP2EO	0.75	124-346
	4-n-octylphenol	n-OP	0.75	26-41
	4-tert-octylphenol	t-OP	3.7	<LOD-17
	4-nonylphenol	NP	0.75	238-1166
	4-tert-nonylphenol	t-NP	0.75	<LOD

Table 4 .6

 4 Removal efficiencies (%) in the anaerobic unit and in the aerobic units operated at 20 °C (anaerobic mesophilic-aerobic: AA20) and 37 °C (anaerobic mesophilic-aerobic: AA37)

	Alkylphenol	Anaerobic	Aerobic (AA20)	Aerobic (AA37)
	4-tert-octylphenol monoethoxylate	98.5	81.4	93.6
	4-tert-octylphenol diethoxylate	41.9	60.8	87.5
	Nonylphenol monoethoxylate	34.6	61.1	73.2
	Nonylphenol diethoxylate	28.7	71.6	82.8
	4-n-octylphenol	~100	-	-
	4-tert-octylphenol	~100	-	-
	4-nonylphenol	88.3	32.1	63.8
	4-tert-nonylphenol	-	-	-

Table 4 .7

 4 Review of electrochemical treatments of alkylphenols and alkylphenol polyethoxylates (BDD: boron-doped diamond; COD

	chemical oxygen

  al.

		Oxidation
		M n+	M n+1
	Reduction		Reduction
	RX	RH		M n+1	M n
		Fe 0. Core	Iron oxide shell
	M(OH) x		M-Fe-OOH
	Precipitation			Co-Precipitation
	M n+	M n+	Fe 3+ + M n+
		Adsorption
			M n+

Acknowledgements Nadia Morin-Crini and Grégorio Crini (Besançon, France) thanks the FEDER (Fonds Européen de Développment Régional) for its financial support (NIRHOFEX Program: "Innovative materials for wastewater treatment"), the Université de Franche-Comté for the research grant awarded to Guest Professor C. Bradu, and the Région Bourgogne Franche-Comté for the research grant awarded to Guest Researcher C. Cosentino. Ján Derco (Bratislava, Slovak Republic) thanks the Agency for Research and Development for the financial support that made it possible to carry out part of the work described in this chapter (contract n° APVV-0656-12).