Wenyu Huang
email: huangwenyu@gxu.edu.cn

Ying Huang
email: huangying_ing@163.com

Shuangfei Wang
email: wangsf@gxu.edu.cn

Hongfei Lin

Gilles Mailhot
email: gilles.mailhot@uca.fr

Degradation of 2,4-Dichlorophenol by Ethylenediamine-N,Ndisuccinic Acid-Modified Photo-Fenton System: Effects of Chemical Compounds Present in Natural Waters

Keywords: photo-Fenton, EDDS, 2,4-DCP, organic matter, inorganic ions, natural water bodies

This paper describes a study of the treatment of 2,4-dichlorophenol (2,4-DCP) with an ethylenediamine-N,N -disuccinic-acid (EDDS)-modified photo-Fenton system in ultrapure water and different natural waters. The results showed that the EDDS-modified photo-Fenton system is adequate for 2,4-DCP degradation. Compared with a medium containing a single organic pollutant, the removal of pollutants in a more complex medium consisting of two organic compounds is slower by around 25 to 50% as a function of the organic pollutant. Moreover, 2,4-DCP can be further effectively degraded in the presence of organic materials and various inorganic ions. However, the photodegradation of 2,4-DCP in different natural waters, including natural lake water, effluent from domestic sewage treatment plants, and secondary effluent from pulp and paper mill wastewaters, is inhibited. Chemical compounds present in natural waters have different influences on the degradation of 2,4-DCP by adopting the EDDS-modified photo-Fenton system. In any case, the results obtained in this work show that the EDDS-modified photo-Fenton system can effectively degrade pollutants in a natural water body, which makes it a promising technology for treating pollutants in natural water bodies.

Introduction

Advanced oxidation processes (AOPs) can effectively oxidize organic pollutants in water using active free radicals [START_REF] Glaze | Advanced Oxidation Processes. A Kinetic Model for the Oxidation of 1,2-Dibromo-3chloropropane in Water by the Combination of Hydrogen Peroxide and UV Radiation[END_REF], which have been adopted to degrade pollutants from many types of wastewaters, such as tannery wastewaters and pharmaceutical wastewaters [START_REF] Sivagami | Advanced oxidation processes for the treatment of tannery wastewater[END_REF][START_REF] Kanakaraju | Advanced oxidation process-mediated removal of pharmaceuticals from water: A review[END_REF]. Fenton technology is one of the most simple and effective AOPs to degrade pollutants [START_REF] Pignatello | Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry[END_REF]. However, the Fenton reaction consumes a large number of chemical reagents and produces toxic by-products, resulting in secondary contamination [START_REF] Fatta-Kassinos | Transformation products of pharmaceuticals in surface waters and wastewater formed during photolysis and advanced oxidation processes-Degradation, elucidation of byproducts and assessment of their biological potency[END_REF]. In order to overcome the shortcomings of Fenton processes, different attempts have been carried out. First of all, irradiation has been introduced in the Fenton reaction, and the Fe(III)/H 2 O 2 mixture (Fenton-like reagent) can absorb photons of wavelengths up to 550 nm [START_REF] Pignatello | Evidence for an Additional Oxidant in the Photoassisted Fenton Reaction[END_REF][START_REF] Pérez | Removal of organic contaminants in paper pulp treatment effluents under Fenton and photo-Fenton conditions[END_REF]. The efficiency of the photo-Fenton process has been proven by many previous studies, most of which were carried out at an acidic pH value [START_REF] Cruz | Study of the contribution of homogeneous catalysis on heterogeneous Fe(III)/alginate mediated photo-Fenton process[END_REF][START_REF] Du | Yolk-shell structured Fe 3 O 4 @void@TiO 2 as a photo-Fenton-like catalyst for the extremely efficient elimination of tetracycline[END_REF][START_REF] Mico | Fosetyl-Al photo-Fenton degradation and its endogenous catalyst inhibition[END_REF]. Additionally, the introduction of chelating agents, especially organic carboxylic acid into the Fenton reaction, proved to be an effective method for broadening the applicable pH values. Several different organic carboxylic acids, such as citric acid, oxalic acid, NTA, and EDTA, were used to modify the Fenton process and proved to be efficient [START_REF] Borba | Pollutant removal and acute toxicity assessment (Artemia salina) of landfill leachate treated by photo-Fenton process mediated by oxalic acid[END_REF][START_REF] Cuervo Lumbaque | Solar photo-Fentonlike process at neutral pH: Fe(III)-EDDS complex formation and optimization of experimental conditions for degradation of pharmaceuticals[END_REF][START_REF] Liu | Preparation and photo-fenton degradation activity of α-Fe2O3 nanorings obtained by adding H2PO4-, SO42-, and citric acid[END_REF][START_REF] Mejri | Fe(3+)-NTA as iron source for solar photo-Fenton at neutral pH in raceway pond reactors[END_REF]. Ethylenediamine-N,N -disuccinic-acid (EDDS), a biodegradable isomer of EDTA, was used as a chelating agent in homogeneous and heterogeneous Fenton and photo-Fenton systems in our previous studies [START_REF] Huang | Enhanced heterogeneous photo-Fenton process modified by magnetite and EDDS: BPA degradation[END_REF][START_REF] Huang | Development of a new homogenous photo-Fenton process using Fe(III)-EDDS complexes[END_REF][START_REF] Huang | Effect of ethylenediamine-N,N -disuccinic acid on Fenton and photo-Fenton processes using goethite as an iron source: Optimization of parameters for bisphenol A degradation[END_REF][START_REF] Huang | Assessment of the Fe(III)-EDDS complex in Fenton-like processes: From the radical formation to the degradation of bisphenol A[END_REF]. Therefore, the EDDS-modified photo-Fenton reaction is proven to be a promising approach to treat refractory pollutants.

However, most laboratory studies on pollutant removal using the EDDS-modified photo-Fenton system are currently conducted using deionized water, which is far from the complex chemical composition of natural water, in which the inorganic ions and dissolved organic compounds in water can significantly influence pollutant removal. In previous research, it was found that the water matrix could significantly influence the efficiency and mechanism of AOPs processes, especially the Fenton process. The presence of common inorganic ions had no substantial effect on herbicide removal when using the photo-Fenton system, but the H 2 O 2 (oxidant) consumption of this reaction was higher than that of the same reaction where inorganic ions were absent [START_REF] Conte | Photo-Fenton degradation of a herbicide (2,4-D) in groundwater for conditions of natural pH and presence of inorganic anions[END_REF]. In the process of the photodegradation of 2,4-D by the photo-Fenton reaction, carbonate has little adverse effects, fluoride has a positive effect, and phosphate has an inhibitory effect [START_REF] Gutierrez-Zapata | 2,4-D abatement from groundwater samples by photo-Fenton processes at circumneutral pH using naturally iron present. Effect of inorganic ions[END_REF]. The effect of typical inorganic water constituents (carbonates and chloride ions) and organic matter was also investigated and found to be different in the UVA-UVB activation of hydrogen peroxide and persulfate for advanced oxidation processes [START_REF] Huang | UVA-UVB activation of hydrogen peroxide and persulfate for advanced oxidation processes: Efficiency, mechanism and effect of various water constituents[END_REF]. Therefore, it is necessary to study the influence of the natural water matrix on pollutant degradation efficiency in the EDDS-modified photo-Fenton system, including not only single inorganic ions or organic compounds but also natural water where various chemical compounds are present.

Chlorophenols (CPs) in wastewater represent a type of pollutant that greatly harms human health and the environment because they are toxic, teratogenic, and carcinogenic [START_REF] Wu | Sorption behavior of 2,4-dichlorophenol on marine sediment[END_REF][START_REF] Karci | Transformation of 2,4-dichlorophenol by H 2 O 2 /UV-C, Fenton and photo-Fenton processes: Oxidation products and toxicity evolution[END_REF]. Nowadays, CPs are widespread in the environment, even in the most remote natural environments, as well as in aquatic and terrestrial food chains [START_REF] Wolfenden | Handbook of Environmental Fate and Exposure Data for Organic Chemicals[END_REF]. Among them, 2,4-DCP is present in most wastewaters generated by the textile and the pulp and papermaking industries and has attracted considerable attention because it is highly toxic and difficult to degrade. Furthermore, it is a kind of absorbable organic halide (AOX), which is the main pollution product in the pulping and papermaking industry [START_REF] Zhang | Effect of hot chlorine dioxide delignification on AOX in bagasse pulp wastewater[END_REF]. It is poisonous, carcinogenic, and teratogenic. Direct discharge into water bodies can cause serious damage to the water environment. As a result, 2,4-DCP is usually degraded by AOPs and used as a target pollutant for developing new AOP methods.

In our previous study, we confirmed that the EDDS-modified photo-Fenton system can effectively degrade 2,4-DCP in deionized water in the laboratory. The effect of pH, H 2 O 2 concentration, and Fe(III)-EDDS dosage was investigated, and the optimal condition was determined [START_REF] Huang | Two amino polycarbonate modified light-Fenton systems: 2,4dechlorophenol degradation[END_REF]. On the other hand, it was found that 2,4-DCP could be effectively degraded in the EDDS-modified photo-Fenton system at pH 3-7. Furthermore, •OH radicals were found to be the main active species of degradation. In this study, our purpose is to reveal the effect of chemical compounds (organic and inorganic compounds) on 2,4-DCP degradation using the EDDS-modified photo-Fenton system and the effect of the complex water matrix on the system. First, the effects of organic matter such as humic acids (HAs) (representing common organic matter in natural water) and 2,4,6-trichlorophenol (2,4,6-TCP) (representing the same kind of organic compounds always accompanying wastewater) on the degradation of 2,4-DCP are discussed. Second, the effects of inorganic ions on 2,4-DCP degradation are evaluated. Finally, three types of natural waters, including natural lake water (NLW), effluent from domestic sewage treatment plants (DSTP), and secondary effluent from pulp and paper mill wastewater (PPMW), are selected as the natural water matrix for 2,4-DCP degradation in the EDDS-modified photo-Fenton reaction. A metal halide lamp is used to mimic sunlight during these laboratory experiments. The expected selectivity of the EDDS-modified photo-Fenton reaction for 2,4-DCP in natural water is demonstrated by comparing the decrease in 2,4-DCP content in pure water with that in different natural waters. The results of these experiments on the efficiency of the EDDS-modified photo-Fenton system in removing pollutants from natural waters have important practical implications for advancing water treatment technologies.

Materials and Methods

Chemicals

EDDS (35% in water) was purchased from Shanghai Anpu Experimental Technology Co., Ltd. (Shanghai, China). 2,4-DCP and 2,4,6-TCP were purchased from Shanghai Macklin Biochemical (Shanghai, China). Ferric chloride hexahydrate, sodium chloride, sodium sulfate, sodium carbonate, sodium nitrate, sodium phosphate dodecahydrate, potassium chloride, magnesium chloride, calcium chloride, and H 2 O 2 (30% in water) were purchased from Guangdong Guanghua Sci-Tech Co., Ltd. (Guangzhou, China). Humic acids (HAs) were purchased from Alfa (Shanghai, China). Methyl alcohol (HPLC grade) and acetonitrile (HPLC grade) were purchased from MERCK (Shanghai, China). The pH of the solutions was adjusted with sodium hydroxide (NaOH) and hydrochloric acid (HCl). The ferric carboxylic acid complex solution was prepared by mixing iron and EDDS aqueous solutions in a ratio of 1:1 (and left to stand for more than 1 h to ensure excellent chelation efficiency).

Analytical Procedures

Total organic carbon (TOC) was measured using an Analytikjena TOC-VCSN analyzer (Jena, Gremany). An ICS-5000 ion chromatography (IC) unit (Dionex Corporation, Sunnyvale, CA, USA) was used to monitor the release of chloride ions; this unit was equipped with a conductivity detector, an anion self-regenerating suppressor (ASRS TM 300 × 4 mm, Dionex Corporation, Sunnyvale, CA, USA), and the AutoSuppression TM Recycle Mode. Ultrapure water and 250 mM NaOH were supplied as the eluent to IC at a flow rate of 1 mL min -1 . Degradation of 2,4-DCP, 2,4,6-TCP, and a mixture of 2,4-DCP and 2,4,6-TCP was determined using ultra-high-pressure liquid chromatography (Waters ACQUITY UPLC ® H-Class, C-18 column, UV detector) (Waters, Milford, MA, USA). The UPLC operating conditions for the target compounds are listed in Table 1.

Experimental System

All experiments were performed in a cylindrical Plexiglas container, which was covered with aluminum foil to protect against light and avoid side photochemical processes, placed on a homemade photoreactor (Figure 1). The photoreactor was designed with a cylindrical container, and the lamp with a glass-jacket was fixed through the central axes of the cell. For the experiment, the target pollutant solution and the Fe(III)-EDDS complex solution (0.1 mM) were added to a 1 L beaker. An adequate volume of the mixture was sampled and transferred into a 1 L volumetric flask, to which hydrogen peroxide solution (1.0 mM) was added. The 1 L flask containing the reaction solution was placed under agitation in a reactor equipped with a metal halide lamp (continuous spectrum of 290-800 nm), and samples were taken from the reactor at different time intervals. In order to simulate the natural pH, the initial pH value of all the single-effect experiments was set close to 7.0. Since the reaction may have continued after sampling, methanol was added to stop the reaction.

sampled and transferred into a 1 L volumetric flask, to which hydrogen peroxide solution (1.0 mM) was added. The 1 L flask containing the reaction solution was placed under agitation in a reactor equipped with a metal halide lamp (continuous spectrum of 290-800 nm), and samples were taken from the reactor at different time intervals. In order to simulate the natural pH, the initial pH value of all the single-effect experiments was set close to 7.0. Since the reaction may have continued after sampling, methanol was added to stop the reaction.

Results

Effects of Organic Matter

Effect of Organic Compounds

Changes in pollutant concentration could significantly influence the degradation efficiency in the photo-Fenton system. Therefore, the influence of different initial concentrations of 2,4-DCP on the photochemical experiment was studied while keeping the other reaction parameters unchanged. The pollutant was almost completely degraded at concentrations of 5 to 20 mg L -1 . For 2,4-DCP concentrations equal to or exceeding 20 mg L -1 , the degradation rate and efficiency decreased as the 2,4-DCP concentration increased (Figure 2). This phenomenon can be interpreted because the number of hydroxyl radicals did not increase proportionally as the pollutant concentration increased [START_REF] Gomathi Devi | Effect of various inorganic anions on the degradation of Congo Red, a di azo dye, by the photo-assisted Fenton process using zero-valent metallic iron as a catalyst[END_REF]. 2,4-DCP exhibited a significant degradation efficiency of around 53% even at the maximum pollutant concentration of 100 mg L -1 considered in this study. The experimental results show that the EDDS-modified photo-Fenton process had an obvious degradation effect on 2,4-DCP, even at high initial concentrations.

Results

Effects of Organic Matter

Effect of Organic Compounds

Changes in pollutant concentration could significantly influence the degradation efficiency in the photo-Fenton system. Therefore, the influence of different initial concentrations of 2,4-DCP on the photochemical experiment was studied while keeping the other reaction parameters unchanged. The pollutant was almost completely degraded at concentrations of 5 to 20 mg L -1 . For 2,4-DCP concentrations equal to or exceeding 20 mg L -1 , the degradation rate and efficiency decreased as the 2,4-DCP concentration increased (Figure 2). This phenomenon can be interpreted because the number of hydroxyl radicals did not increase proportionally as the pollutant concentration increased [START_REF] Gomathi Devi | Effect of various inorganic anions on the degradation of Congo Red, a di azo dye, by the photo-assisted Fenton process using zero-valent metallic iron as a catalyst[END_REF]. 2,4-DCP exhibited a significant degradation efficiency of around 53% even at the maximum pollutant concentration of 100 mg L -1 considered in this study. The experimental results show that the EDDS-modified photo-Fenton process had an obvious degradation effect on 2,4-DCP, even at high initial concentrations. The toxicity of CPs can be ascribed to the number of Cl atoms on the benzene ring: the more Cl atoms in the chemical formula of CPs, the more toxic organic compounds there are [START_REF] Liu | Three-dimensional quantitative structure activity relationship (3D-QSAR) analysis for in vitro toxicity of chlorophenols to HepG2 cells[END_REF]. Moreover, the quantity of Cl atoms on the benzene ring may affect the rate of degradation. Accordingly, we experimentally investigated the degradation of single 2,4,6-TCP and 2,4-DCP, as well as that of a mixture of these two pollutants. The toxicity of CPs can be ascribed to the number of Cl atoms on the benzene ring: the more Cl atoms in the chemical formula of CPs, the more toxic organic compounds there are [START_REF] Liu | Three-dimensional quantitative structure activity relationship (3D-QSAR) analysis for in vitro toxicity of chlorophenols to HepG2 cells[END_REF]. Moreover, the quantity of Cl atoms on the benzene ring may affect the rate of degradation. Accordingly, we experimentally investigated the degradation of single 2,4,6-TCP and 2,4-DCP, as well as that of a mixture of these two pollutants.

In our photo-Fenton system and the single-substance experiments, the rate of 2,4-DCP pollutant removal was superior by around 65% to those of 2,4,6-TCP (Figure 3). This difference in 2,4-DCP and 2,4,6-TCP degradation rates could be attributed to the number of chlorine atoms on these CPs, possibly because the OH and Cl groups of 2,4-DCP are aligned along the ortho and para directions, and the •OH radicals have the same preference for attack. By contrast, steric hindrance prevents the hydroxylation of 2,4,6-TCP [START_REF] Tang | The effect of chlorine position of chlorinated phenols on their dechlorination kinetics by Fenton's reagent[END_REF]. It was reported that in the heterogeneous photo-Fenton system, the 4-CP removal rate was superior to that of 2,4,6-TCP, indicating that the quantity of Cl atoms significantly influenced the phenolic compounds' degradation rate [START_REF] Del Campo | Photo-Fenton oxidation of phenolic compounds catalyzed by iron-PILC[END_REF]. However, our results showed the same effect but also that the EDDS-modified photo-Fenton process can be used to effectively treat 2,4-DCP and 2,4,6-TCP pollutants in deionized water.

Given that wastewaters contain multiple organic matters, we performed other experiments with a mixture of two soluble pollutant compounds (2,4-DCP and 2,4,6-TCP). The individual concentrations of 2,4-DCP and 2,4,6-TCP were set to 10 mg L -1 (total pollutant concentration is 20 mg L -1 ) while keeping the other experimental conditions unchanged from those employed in the single-substance experiments.

The removal rate of residual pollutants after 20 min of irradiation was considerably slower than that before 20 min of irradiation (Figures 3 and4). This was primarily ascribed to the low concentration of residual pollutants (around 20% in the single-pollutant experiment and 40% in the mixture of the two pollutants of the initial concentration) after the first 20 min of reaction, resulting in a higher competition reaction of •OH radicals with Fe 2+ and H 2 O 2 able to scavenge •OH radicals as well [START_REF] Zhang | Kinetics study on the degradation of a model naphthenic acid by ethylenediamine-N,N -disuccinic acid-modified Fenton process[END_REF][START_REF] Catastini | Iron (III) aquacomplexes as effective photocatalysts for the degradation of pesticides in homogeneous aqueous solutions[END_REF][START_REF] El-Morsi | Homogeneous degradation of 1,2,9,10tetrachlorodecane in aqueous solutions using hydrogen peroxide, iron and UV light[END_REF].

preference for attack. By contrast, steric hindrance prevents the hydroxylation of TCP [START_REF] Tang | The effect of chlorine position of chlorinated phenols on their dechlorination kinetics by Fenton's reagent[END_REF]. It was reported that in the heterogeneous photo-Fenton system, the 4-C moval rate was superior to that of 2,4,6-TCP, indicating that the quantity of Cl atom nificantly influenced the phenolic compounds' degradation rate [START_REF] Del Campo | Photo-Fenton oxidation of phenolic compounds catalyzed by iron-PILC[END_REF]. However, o sults showed the same effect but also that the EDDS-modified photo-Fenton proces be used to effectively treat 2,4-DCP and 2,4,6-TCP pollutants in deionized water.

Given that wastewaters contain multiple organic matters, we performed other e iments with a mixture of two soluble pollutant compounds (2,4-DCP and 2,4,6-TCP individual concentrations of 2,4-DCP and 2,4,6-TCP were set to 10 mg L -1 (total pol concentration is 20 mg L -1 ) while keeping the other experimental conditions uncha from those employed in the single-substance experiments.

The removal rate of residual pollutants after 20 min of irradiation was conside slower than that before 20 min of irradiation (Figures 3 and4). This was primarily asc to the low concentration of residual pollutants (around 20% in the single-pollutant e iment and 40% in the mixture of the two pollutants of the initial concentration) aft first 20 min of reaction, resulting in a higher competition reaction of •OH radicals Fe 2+ and H2O2 able to scavenge •OH radicals as well [START_REF] Zhang | Kinetics study on the degradation of a model naphthenic acid by ethylenediamine-N,N -disuccinic acid-modified Fenton process[END_REF][START_REF] Catastini | Iron (III) aquacomplexes as effective photocatalysts for the degradation of pesticides in homogeneous aqueous solutions[END_REF][START_REF] El-Morsi | Homogeneous degradation of 1,2,9,10tetrachlorodecane in aqueous solutions using hydrogen peroxide, iron and UV light[END_REF]. In the two-pollutants experiment, approximately 80% of the two are degrade 120 min. Compared with the single-pollutant experiment, the removal rate of the tw lutants was lower by around 54% for 2,4-DCP and 24% for 2,4,6-TCP. This result i that the degradation of pollutants in complex media is slower. Therefore, our demonstrate that the EDDS-modified photo-Fenton system is very effective for tre single organic pollutant or a mixture of two organic pollutants.

The apparent rate constant of degradation of mixed pollutants is lower than th single pollutant (Figures 3b and4b), which indicates that 2,4-DCP degradation w significantly affected in more complex natural media (a detailed analysis of 2,4-DC radation in complex natural media is provided in Section 3.3). Compared with a m containing a single pollutant, a medium containing two organic pollutants will de the removal rate and weaken the removal effect. Nevertheless, in this experime main goal (of pollutant removal) was achieved within a reasonable timespan.

Effect of Humic Acids (HAs)

HAs are ubiquitous in aquatic environments [START_REF] Fukushima | Degradation characteristics of humic acid during photo-Fenton processes[END_REF]. To a large extent, the degra of organic pollutants is affected by their interaction with dissolved organic matter such as HA) in aquatic environments [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF]. When DOM absorbs ultraviolet or solar tion, it forms reactive oxygen intermediates and can also have a shielding effect a hibits the AOPs [START_REF] Mill | Predicting photoreaction rates in surface waters[END_REF][START_REF] Konstantinou | Photodegradation of Selected Herbicides in Various Natural Waters and Soils under Environmental Conditions[END_REF]. DOM can enhance or inhibit the photodegradation rate [ DOM in water, such as HA, can trap •OH radicals and also produce •OH radicals irradiation [START_REF] Derbalah | Photocatalytic removal of fenitrothion in pure and natural waters by photo-Fenton reaction[END_REF]. HA is a potential electron donor and can reduce Fe 3+ in the syste example, HA can significantly improve the degradation effect of pentachlorophe promoting the redox cycles of Fe(III) and Fe(II) in the photo-Fenton system [START_REF] Deng | Kinetics of redox cycling of iron coupled with fulvic acid[END_REF][START_REF] Fukushima | Degradation pathways of pentachlorophenol by photo-Fenton systems in the presence of iron(III), humic acid, and hydrogen peroxide[END_REF]. fore, it is necessary to study the influence of HA on pollutant degradation in natural In our study, when HA was present in the solutions, the degradation rate of the modified photo-Fenton system decreased marginally (around 10% less after 120 In the two-pollutants experiment, approximately 80% of the two are degraded after 120 min. Compared with the single-pollutant experiment, the removal rate of the two pollutants was lower by around 54% for 2,4-DCP and 24% for 2,4,6-TCP. This result implies that the degradation of pollutants in complex media is slower. Therefore, our results demonstrate that the EDDS-modified photo-Fenton system is very effective for treating a single organic pollutant or a mixture of two organic pollutants.

The apparent rate constant of degradation of mixed pollutants is lower than that of a single pollutant (Figures 3b and4b), which indicates that 2,4-DCP degradation will be significantly affected in more complex natural media (a detailed analysis of 2,4-DCP degradation in complex natural media is provided in Section 3.3). Compared with a medium containing a single pollutant, a medium containing two organic pollutants will decrease the removal rate and weaken the removal effect. Nevertheless, in this experiment, the main goal (of pollutant removal) was achieved within a reasonable timespan.

Effect of Humic Acids (HAs)

HAs are ubiquitous in aquatic environments [START_REF] Fukushima | Degradation characteristics of humic acid during photo-Fenton processes[END_REF]. To a large extent, the degradation of organic pollutants is affected by their interaction with dissolved organic matter (DOM, such as HA) in aquatic environments [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF]. When DOM absorbs ultraviolet or solar radiation, it forms reactive oxygen intermediates and can also have a shielding effect and inhibits the AOPs [START_REF] Mill | Predicting photoreaction rates in surface waters[END_REF][START_REF] Konstantinou | Photodegradation of Selected Herbicides in Various Natural Waters and Soils under Environmental Conditions[END_REF]. DOM can enhance or inhibit the photodegradation rate [START_REF] Kamiya | Photochemical effects of humic substances on the degradation of organophosphorus pesticides[END_REF][START_REF] Bachman | Photodecomposition of the Carbamate Pesticide Carbofuran: Kinetics and the Influence of Dissolved Organic Matter[END_REF]. DOM in water, such as HA, can trap •OH radicals and also produce •OH radicals under irradiation [START_REF] Derbalah | Photocatalytic removal of fenitrothion in pure and natural waters by photo-Fenton reaction[END_REF]. HA is a potential electron donor and can reduce Fe 3+ in the system. For example, HA can significantly improve the degradation effect of pentachlorophenol by promoting the redox cycles of Fe(III) and Fe(II) in the photo-Fenton system [START_REF] Deng | Kinetics of redox cycling of iron coupled with fulvic acid[END_REF][START_REF] Fukushima | Degradation pathways of pentachlorophenol by photo-Fenton systems in the presence of iron(III), humic acid, and hydrogen peroxide[END_REF]. Therefore, it is necessary to study the influence of HA on pollutant degradation in natural water. In our study, when HA was present in the solutions, the degradation rate of the EDDS-modified photo-Fenton system decreased marginally (around 10% less after 120 min of irradiation). Moreover, when the HA concentration was increased from 2 to 5 mg L -1 , the 2,4-DCP degradation rate was almost unchanged (Figure 5).

Processes 2021, 9, x FOR PEER REVIEW 9 of 18 irradiation). Moreover, when the HA concentration was increased from 2 to 5 mg L -1 , the 2,4-DCP degradation rate was almost unchanged (Figure 5). The lower degradation rate could be ascribed to the fact that HA scavenged •OH radicals. Moreover, HA and the Fe(III)-EDDS complex compete for light absorption because HA is known to absorb sunlight, which reduces the photoredox process of the iron complex [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF][START_REF] Epling | Investigation of retardation effects on the titanium dioxide photodegradation system[END_REF]. The photochemical properties of HA can be ascribed to complex phenomena and are influenced by multiple factors, including its origin and structural characteristics [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF][START_REF] Aguer | Comparison of the photoinductive properties of commercial, synthetic and soil-extracted humic substances[END_REF].

Effects of Inorganic Ions

The results above indicate that the EDDS-modified photo-Fenton process is a promising and novel technology that can completely degrade 2,4-DCP. However, industrial wastewaters contain various inorganic ions. These inorganic anions and cations can play complex roles in the EDDS-modified photo-Fenton process.

Cl -and SO4 2-ions could reduce the reaction efficiency by scavenging hydroxyl radicals and competing with the ligand for the complexation of iron ions [START_REF] Evgenidou | Oxidation of two organophosphorous insecticides by the photo-assisted Fenton reaction[END_REF]. The reaction of •OH radicals with SO4 2-ions occurs only at very high concentrations of SO4 2-ions [START_REF] Pignatello | Dark and photoassisted iron(3+)-catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide[END_REF]. Indeed, compared with the control experiment, the addition of SO4 2-(at concentrations of 100 to 200 mM) can marginally improve the 2,4-DCP photodegradation rate of the EDDSmodified photo-Fenton system (Figure 6a). The lower degradation rate could be ascribed to the fact that HA scavenged •OH radicals. Moreover, HA and the Fe(III)-EDDS complex compete for light absorption because HA is known to absorb sunlight, which reduces the photoredox process of the iron complex [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF][START_REF] Epling | Investigation of retardation effects on the titanium dioxide photodegradation system[END_REF]. The photochemical properties of HA can be ascribed to complex phenomena and are influenced by multiple factors, including its origin and structural characteristics [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF][START_REF] Aguer | Comparison of the photoinductive properties of commercial, synthetic and soil-extracted humic substances[END_REF].

Effects of Inorganic Ions

The results above indicate that the EDDS-modified photo-Fenton process is a promising and novel technology that can completely degrade 2,4-DCP. However, industrial wastewaters contain various inorganic ions. These inorganic anions and cations can play complex roles in the EDDS-modified photo-Fenton process.

Cl -and SO 4 2-ions could reduce the reaction efficiency by scavenging hydroxyl radicals and competing with the ligand for the complexation of iron ions [START_REF] Evgenidou | Oxidation of two organophosphorous insecticides by the photo-assisted Fenton reaction[END_REF]. The reaction of •OH radicals with SO 4 2-ions occurs only at very high concentrations of SO 4 2-ions [START_REF] Pignatello | Dark and photoassisted iron(3+)-catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide[END_REF]. Indeed, compared with the control experiment, the addition of SO 42-(at concentrations of 100 to 200 mM) can marginally improve the 2,4-DCP photodegradation rate of the EDDS-modified photo-Fenton system (Figure 6a). From our results (Figure 6a), we show that the 2,4-DCP degradation efficiency decreased slightly at the chloride concentration up to 7.10 g/L, and the process continued to exhibit a significant degradation efficiency. The addition of chlorine ions to an aqueous solution of iron ions will result in the formation of the Fe(Cl) 2+ complex, which has a weaker (photo)reactivity than the Fe(III)-EDDS complex (R1) [START_REF] Devi | Effect of chloride and sulfate ions on the advanced photo Fenton and modified photo Fenton degradation process of Alizarin Red S[END_REF]. The effect of the concentration of chlorine ions is complicated in Fenton chemistry. When the Cl -concentration is equal to 17.75 g/L, the 2,4-DCP degradation efficiency is higher than when a 7.10 g/L Cl - From our results (Figure 6a), we show that the 2,4-DCP degradation efficiency decreased slightly at the chloride concentration up to 7.10 g/L, and the process continued to exhibit a significant degradation efficiency. The addition of chlorine ions to an aqueous solution of iron ions will result in the formation of the Fe(Cl) 2+ complex, which has a weaker (photo)reactivity than the Fe(III)-EDDS complex (R1) [START_REF] Devi | Effect of chloride and sulfate ions on the advanced photo Fenton and modified photo Fenton degradation process of Alizarin Red S[END_REF]. The effect of the concentration of chlorine ions is complicated in Fenton chemistry. When the Cl -concentration is equal to 17.75 g/L, the 2,4-DCP degradation efficiency is higher than when a 7.10 g/L Cl -concentration is added and lower than that in the deionized aqueous solution. This may be because of the increased concentration of chloride ions and the formation of Cl • radicals by the Fe(Cl) 2+ complex under irradiation (R2), which contribute toward 2,4-DCP degradation. The activity of Cl • radicals is weaker than that of •OH radicals [START_REF] Neta | Rate Constants for Reactions of Inorganic Radicals in Aqueous Solution[END_REF][START_REF] Dong | Decoloration of three azo dyes in water by photocatalysis of Fe (III)-oxalate complexes/H 2 O 2 in the presence of inorganic salts[END_REF]. The inhibitory effect of chloride should also be attributed to the reactivity of •OH radical with Cl -leading to the formation of Cl • radical or ClOH • -and after Cl • radical reacts with Cl -to form the radical Cl 2

• - [START_REF] Devi | Photo-degradation of di azo dye Bismarck Brown by advanced photo-Fenton process: Influence of inorganic anions and evaluation of recycling efficiency of iron powder[END_REF][START_REF] Soler | Effect of inorganic ions on the solar detoxification of water polluted with pesticides[END_REF]. These reactions are significant in the presence of •OH radicals and Cl -.

Fe 3+ + Cl -→ Fe(Cl) 2+ (1)
Fe(Cl) 2+ + hv → Fe 2+ + Cl • (2)
We found that NO 3 -ions had a small effect on the system. When the NO 3 -ion concentration was increased, the degradation rate slightly increased (Figure 6a). NO 3 ions can produce other •OH radicals (R3 and R4) under irradiation. However, NO 3

-ions have a strong ultraviolet (UV)-shielding effect, which is more significant than the formation of •OH radicals through NO 3

-photolysis [START_REF] Sillanpaa | Degradation of chelating agents in aqueous solution using advanced oxidation process (AOP)[END_REF]. The fact that the presence of NO 3 -ions did not significantly influence the degradation of 2,4-DCP can possibly be ascribed to the interaction of all the above mentioned factors.

NO - 3 + hv → NO - 2 + O(3P) (3)
NO - 3 + H + + hv → NO • 2 + HO • (4)
On the contrary, the degradation of 2,4-DCP was severely affected by the presence of carbonates (Figure 6a). When the carbonate concentration was 300 mg/L, the 2,4-DCP degradation efficiency decreased by approximately 25%. It has been reported that carbonates play an essential role in AOPs by acting as scavengers of hydroxyl radicals through the reaction R5, increasing oxidant consumption [START_REF] Miralles-Cuevas | Pharmaceuticals removal from natural water by nanofiltration combined with advanced tertiary treatments (solar photo-Fenton, photo-Fenton-like Fe(III)-EDDS complex and ozonation)[END_REF]. Papautsakis et al. [START_REF] Papoutsakis | Benefits and limitations of using Fe(III)-EDDS for the treatment of highly contaminated water at near-neutral pH[END_REF] reported that carbonate can scavenge •OH radicals and inhibit the degradation of imidacloprid in the Fe-EDDS photo-Fenton process. Moreover, carbonate has also been shown to have a destructive effect on the stability of soluble iron [START_REF] Miralles-Cuevas | Pharmaceuticals removal from natural water by nanofiltration combined with advanced tertiary treatments (solar photo-Fenton, photo-Fenton-like Fe(III)-EDDS complex and ozonation)[END_REF].

CO 2- 3 + HO • → CO •- 3 + OH - (k = 3.9 × 10 8 M -1 s -1 ) (5)
As the phosphate concentration increased, the 2,4-DCP degradation rate decreased, indicating that the PO 4 3-ion forms a complex with Fe 3+ and reduces the efficiency of the EDDS-modified photo-Fenton system. It is reported in the literature that Fe 3+ precipitation by PO 4 3-limited the Fenton and photo-Fenton reactions in aqueous solutions with high phosphate concentrations [START_REF] Klamerth | Photo-Fenton decomposition of chlorfenvinphos: Determination of reaction pathway[END_REF].

It is known that pH significantly influences the Fenton process. In the presence of carbonates and phosphates, the solution pH has a buffering capacity, owing to the hydrolysis of PO 4 3-and CO 3 2-ions. Under this condition, the solution pH is neutral at the end of the experiment, while in deionized water, the corresponding solution pH is approximately 4.8. This may be also an important reason for the effect of carbonate and phosphate ions on the removal of pollutants.

When K + , Ca 2+ , and Mg 2+ ions were present in the solution, the degradation efficiency of the system decreased slightly (Figure 6b). Metal cations affect the degradation of the system by competing with Fe(III) ions for ligands. It has been shown that the higher the number of charges of metal ions, the greater their complexation ability [START_REF] Chang | Desorption of tetracycline from montmorillonite by aluminum, calcium, and sodium: An indication of intercalation stability[END_REF]. The complexation ability of Fe 3+ ions is the strongest, followed by Ca 2+ and Mg 2+ ions, and K + ions are the weakest. Therefore, even in the case of very high K + concentration, the effect on the system is very small.

The above results made clear that the EDDS-modified photo-Fenton process can efficiently degrade organic pollutants in the presence of inorganic ions. Even at high concentrations of inorganic ions, the EDDS-modified photo-Fenton system exhibited significant degradation efficiency. Furthermore, inorganic ions affect degradation mainly by competing with trivalent iron for ligands and scavenging hydroxyl radicals. Therefore, an investigation of 2,4-DCP degradation using the EDDS-modified photo-Fenton system in the presence of the main constituents of water will help to improve our understanding of their effects on pollutant degradation in real aquatic systems.

Effect of Natural Water Bodies

TOC and ionic chromatography analyses of the three natural water bodies show significantly different matrix contents. In terms of ions, the amounts of Cl -, NO 3 -, and SO 4 2-detected in the DSTP, PPMW, and NLW water samples varied significantly. NO 3 was not detected in NLW (Table 2). The chromaticity of the three water bodies varied considerably, which is of great importance for the photo-Fenton system. In conclusion, the chemical compositions of the three water samples differed considerably, and the influences of ion concentration and chromaticity were non-negligible.

Not detected

Pollutant degradation in natural water is a more complex process than degradation in the presence of single inorganic ions and organic matter. The EDDS-modified photo-Fenton system was used to evaluate the photocatalytic removal of 2,4-DCP dissolved in natural waters, including NLW, DSTP, and PPMW. The 2,4-DCP degradation rate in deionized water was considerably faster than that in natural waters. The degradation efficiencies after 120 min of irradiation were 52.5%, 64.4%, and 38.5% in DSTP, NLW, and PPWM, respectively (Figure 7) and around 100% in deionized water after 60 min of irradiation.

The lower 2,4-DCP degradation rate in NLW, DSTP, or PPMW than that in deionized water could be ascribed to the presence of inorganic ions and dissolved organic compounds. As given in Table 2, we determined some of the chemical constituents. The concentrations of chloride, sulfate, and nitrate ions in the studied natural waters were different. Among the three aforementioned water systems, 2,4-DCP degradation was most severely inhibited in PPMW, which may be ascribed to the relatively higher concentrations of inorganic ions in this compartment than those in the other two other water systems. Secondly, PPMW is dark yellow in color, which means it can cause a screen effect and thus decrease the Fe(III)-EDDS photoredox process. Thirdly, the presence of higher TC concentration can affect the degradation efficiency of 2,4-DCP. A more comprehensive understanding of the influence of TOC and total inorganic ion concentration in water on pollutant removal is therefore needed. The lower 2,4-DCP degradation rate in NLW, DSTP, or PPMW than that in deionized water could be ascribed to the presence of inorganic ions and dissolved organic compounds. As given in Table 2, we determined some of the chemical constituents. The concentrations of chloride, sulfate, and nitrate ions in the studied natural waters were different. Among the three aforementioned water systems, 2,4-DCP degradation was most severely inhibited in PPMW, which may be ascribed to the relatively higher concentrations of inorganic ions in this compartment than those in the other two other water systems. Secondly, PPMW is dark yellow in color, which means it can cause a screen effect and thus decrease the Fe(III)-EDDS photoredox process. Thirdly, the presence of higher TC concentration can affect the degradation efficiency of 2,4-DCP. A more comprehensive understanding of the influence of TOC and total inorganic ion concentration in water on pollutant removal is therefore needed.

The TOC concentration of NLW, DSTP, and PPMW increased successively, contrary to the decreased 2,4-DCP degradation efficiencies (Figure 8a). The high concentration of TOC in the natural water body was in competition with the target pollutant for the reactivity of •OH radicals, which is an essential reason for the resulting low degradation efficiency. Moreover, compared with that in deionized water, the decreased 2,4-DCP photodegradation efficiency in natural water may be ascribed to the optical filter effect of organic matter in natural water. Indeed, organic matter can be one of the critical absorbers of sunlight in aquatic environments [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF]. We speculate that TOC concentration is not the only factor affecting 2,4-DCP degradation in the studied water bodies. The effect of total inorganic ion concentration in water on 2,4-DCP removal was explored. Overall, the 2,4-DCP degradation efficiency decreased as the total inorganic ion concentration increased (Figure 8b). The same effect was observed in the study by Sakkas et al. [START_REF] Zhang | Effect of hot chlorine dioxide delignification on AOX in bagasse pulp wastewater[END_REF]. As the salinity of water increased, chlorothalonil combined with DOM through hydrophobic interaction or weak van der Waals forces, thus affecting the photodegradation of the pollutants. Obviously, the factors affecting the 2,4-DCP removal in natural water included inorganic ion concentration, TOC concentration, and chromaticity. The TOC concentration of NLW, DSTP, and PPMW increased successively, contrary to the decreased 2,4-DCP degradation efficiencies (Figure 8a). The high concentration of TOC in the natural water body was in competition with the target pollutant for the reactivity of •OH radicals, which is an essential reason for the resulting low degradation efficiency. Moreover, compared with that in deionized water, the decreased 2,4-DCP photodegradation efficiency in natural water may be ascribed to the optical filter effect of organic matter in natural water. Indeed, organic matter can be one of the critical absorbers of sunlight in aquatic environments [START_REF] Sakkas | Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances[END_REF]. We speculate that TOC concentration is not the only factor affecting 2,4-DCP degradation in the studied water bodies. The effect of total inorganic ion concentration in water on 2,4-DCP removal was explored. Overall, the 2,4-DCP degradation efficiency decreased as the total inorganic ion concentration increased (Figure 8b). The same effect was observed in the study by Sakkas et al. [START_REF] Zhang | Effect of hot chlorine dioxide delignification on AOX in bagasse pulp wastewater[END_REF]. As the salinity of water increased, chlorothalonil combined with DOM through hydrophobic interaction or weak van der Waals forces, thus affecting the photodegradation of the pollutants. Obviously, the factors affecting the 2,4-DCP removal in natural water included inorganic ion concentration, TOC concentration, and chromaticity.

The UV-visible absorption spectrum of different water matrices containing 2,4-DCP is shown in Figure 9, and it was noted that most change in UV-visible absorption occurred in the UV zone (lower than 290 nm), which was out of the wavelength range of the lamp used in this study. As a result, it was preliminarily indicated that the influence had nothing to do with UV-visible absorption. The UV-visible absorption spectrum of different water matrices containing 2,4-DCP is shown in Figure 9, and it was noted that most change in UV-visible absorption occurred in the UV zone (lower than 290 nm), which was out of the wavelength range of the lamp used in this study. As a result, it was preliminarily indicated that the influence had nothing to do with UV-visible absorption. The degradation of 2,4-DCP was affected differently by different natural water compositions. However, the more the water is loaded with organic/inorganic compounds, the more significant the inhibition of 2,4-DCP degradation. Regardless, the EDDS-modified photo-Fenton system still removed more than 50% of 2,4-DCP in NLW and DSTP and more than 30% in PPMW. This finding indicates that the EDDS-modified photo-Fenton process can be used to effectively treat pollutants in natural waters and potentially simulate solar photocatalytic water treatment. Thus, 2,4-DCP degradation in natural water bodies justifies a more in-depth study to understand and evaluate the parameters that are essential for the efficiency of the process.

Conclusions

The results indicate that the EDDS-modified photo-Fenton system is suitable for 2,4-DCP removal. It is a promising route for treating 2,4-DCP by simulating natural sunlight, which is a low-cost alternative light source and significantly reduces the process cost. The system could effectively degrade single 2,4-DCP and 2,4,6-TCP pollutants and the mixture of 2,4-DCP and 2,4,6-TCP. Furthermore, it could effectively degrade pollutants in the presence of common inorganic ions. The effect of anions on 2,4-DCP degradation was found to be stronger than that of cations. Finally, the degradations of 2,4-DCP in different water bodies, including NLW, DSTP, and PPMW, were remarkably different. The 2,4-DCP degradation rate in PPMW was severely inhibited, which may be related to the high absorption of light, high TOC concentration, and high inorganic ion content in this water compartment. The use of several different natural waters to treat 2,4-DCP with the EDDSmodified photo-Fenton process shows the efficiency of this process for industrial applications. Nevertheless, the application will be particularly more efficient when this process is used in a ternary treatment when the water is not too loaded.

Figure 1 .

 1 Figure 1. The scheme of the photoreactor used in this study.

Figure 1 .

 1 Figure 1. The scheme of the photoreactor used in this study.

Processes 2021, 9 , 18 Figure 2 .

 9182 Figure 2. 2,4-DCP degradation efficiency for different 2,4-DCP initial concentrations. [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 2 . 2 , 4 -

 224 Figure 2. 2,4-DCP degradation efficiency for different 2,4-DCP initial concentrations. [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, and pH = 7.0 ± 0.1.

Processes 2021, 9 , 18 Figure 3 .

 9183 Figure 3. (a) EDDS-modified photo-Fenton degradation of 2,4-DCP and 2,4,6-TCP. (b) Variation of ln C/C0 with time in 2,4-DCP and 2,4,6-TCP concentration using the EDDS-modified photo-Fenton system. [2,4-DCP] = [2,4,6-TCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, pH = 7.0 ± 0.1. This difference in 2,4-DCP and 2,4,6-TCP degradation rates could be attributed to the number of chlorine atoms on these CPs, possibly because the OH and Cl groups of 2,4-DCP are aligned along the ortho and para directions, and the •OH radicals have the same

Figure 3 .

 3 Figure 3. (a) EDDS-modified photo-Fenton degradation of 2,4-DCP and 2,4,6-TCP. (b) Variation of ln C/C 0 with time in 2,4-DCP and 2,4,6-TCP concentration using the EDDS-modified photo-Fenton system. [2,4-DCP] = [2,4,6-TCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, pH = 7.0 ± 0.1.

Figure 4 .

 4 Figure 4. Cont.

Figure 4 .

 4 Figure 4. EDDS-modified photo-Fenton degradation of a mixture of 2,4-DCP and 2,4,6-TCP in the two-pollutants expe ment. [2,4-DCP] = 10 mg L -1 , [2,4,6-TCP] = 10 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 4 .

 4 Figure 4. EDDS-modified photo-Fenton degradation of a mixture of 2,4-DCP and 2,4,6-TCP in the two-pollutants experiment ((a) 2,4-DCP and 2,4,6-TCP degradation efficiency; (b) apparent rate constant of degradation of mixed pollutants). [2,4-DCP] = 10 mg L -1 , [2,4,6-TCP] = 10 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 5 .

 5 Figure 5. Effect of humic acid (HA) on 2,4-DCP degradation. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 5 .

 5 Figure 5. Effect of humic acid (HA) on 2,4-DCP degradation. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 6 .

 6 Figure 6. Effects of anions and cations on 2,4-DCP degradation. (a) Anions; (b) cations. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 6 .

 6 Figure 6. Effects of anions and cations on 2,4-DCP degradation. (a) Anions; (b) cations. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 7 .

 7 Figure 7. Degradation of 2,4-DCP in natural water bodies. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 7 .

 7 Figure 7. Degradation of 2,4-DCP in natural water bodies. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 8 .

 8 Figure 8. Effects of (a) TOC and (b) total inorganic ion concentration on 2,4-DCP degradation efficiency in different water bodies. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H2O2] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 8 .

 8 Figure 8. Effects of (a) TOC and (b) total inorganic ion concentration on 2,4-DCP degradation efficiency in different water bodies. [2,4-DCP] = 20 mg L -1 , [Fe(III)-EDDS] = 0.1 mM, [H 2 O 2 ] = 1.0 mM, and pH = 7.0 ± 0.1.

Figure 9 .

 9 Figure 9. UV-visible absorption spectrum of different water bodies.

Table 1 .

 1 UPLC methods for target compounds.

	Compound

Mobile Phase Flow Rate (mL min -1 ) Column Temperature ( • C) Injection Volume (µL) Detection Wavelength (nm)

	2,4-DCP	Water/methanol (40:60. v/v)	0.35	35	5	280
	2,4,6-TCP	Water/methanol (20:80. v/v)	0.35	35	5	210
	Mixture of 2,4-DCP and 2,4,6-TCP	Water/methanol (20:80. v/v)	0.35	35	5	Dual channel: 210 and 280

Table 2 .

 2 Physicochemical parameters and chemical compositions of natural water bodies.

	Water Bodies	Color	pH TOC (mg L -1 )	TC (mg L -1 )	IC (mg L -1 )	Anion	Concentration (mg L -1 )
							Cl -	188.1
	PPMW	Dark yellow	7.84	49.8	88.0	38.2	2--NO 3 SO 4 Cl -	67.7 20.1 37.2
	DSTP	Light yellow	7.05	6.6	17.0	10.4	2--NO 3 SO 4 Cl -	21.9 16.4 7.6
	NLW	Yellow	8.47	6.4	9.4	3.0	2-NO 3 SO 4 -	21.8

Processes 2021, 9, 29

Processes 2021, 9, x FOR PEER REVIEW

Processes 2021, 9, x FOR PEER REVIEW

Acknowledgments: This work was partially supported by the National Natural Science Foundation of China (No. 21367003), Guangxi Science and Technology Research Program (No. AA17202032) and Open Fond of Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control (KF201724).

Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

The degradation of 2,4-DCP was affected differently by different natural water compositions. However, the more the water is loaded with organic/inorganic compounds, the more significant the inhibition of 2,4-DCP degradation. Regardless, the EDDS-modified photo-Fenton system still removed more than 50% of 2,4-DCP in NLW and DSTP and more than 30% in PPMW. This finding indicates that the EDDS-modified photo-Fenton process can be used to effectively treat pollutants in natural waters and potentially simulate solar photocatalytic water treatment. Thus, 2,4-DCP degradation in natural water bodies justifies a more in-depth study to understand and evaluate the parameters that are essential for the efficiency of the process.

Conclusions

The results indicate that the EDDS-modified photo-Fenton system is suitable for 2,4-DCP removal. It is a promising route for treating 2,4-DCP by simulating natural sunlight, which is a low-cost alternative light source and significantly reduces the process cost. The system could effectively degrade single 2,4-DCP and 2,4,6-TCP pollutants and the mixture of 2,4-DCP and 2,4,6-TCP. Furthermore, it could effectively degrade pollutants in the presence of common inorganic ions. The effect of anions on 2,4-DCP degradation was found to be stronger than that of cations. Finally, the degradations of 2,4-DCP in different water bodies, including NLW, DSTP, and PPMW, were remarkably different. The 2,4-DCP degradation rate in PPMW was severely inhibited, which may be related to the high absorption of light, high TOC concentration, and high inorganic ion content in this water compartment. The use of several different natural waters to treat 2,4-DCP with the EDDS-modified photo-Fenton process shows the efficiency of this process for industrial applications. Nevertheless, the application will be particularly more efficient when this process is used in a ternary treatment when the water is not too loaded.

Conflicts of Interest:

The authors declare no conflict of interest.


mirko.santoro@cnrs.fr

Typology of compounds in phonological perspective

Mirko Santoro

Goal

• analyse all kind of compounds, sequential and simultaneous ones

• find specific generalizations

•

Santoro (2018)

Simultaneous compound (lexicon) WHAT'S NEXT ?

• Analyse the movement morpheme in compounds that involve classifiers.

  and foreign vocabulary in American Sign Language: a lexicon with multiple origins. In: BRENTARI, D. (ed.) Foreign vocabulary in sign languages. Mahwah, New Jersey: Lawrence Erlbaum Associates. Engberg-Pedersen, E. (1993). Space in Danish Sign Language: The semantics and morphosyntax of the use of space in a visual language. Fenlon, J., Cormier, K., and Brentari, D. (2017). The phonology of sign languages. In S. and Bosch, A., editors, The Routledge handbook of phonological pages 453-475. Routledge.

•

  In simultaneous compounds , the DH carries more semantic content than NDH. I propose that a rule imposes that the DH should involve less phonological process as possible. This rule explains why truncation, which is as a phenomenon of phonological reduction, is never observed on the DH •In simultaneous compounds, a rule is imposes that NDH handshape must be less complex than the DH handshape.

• SASS classifiers are flexible: they can be found in both sequential and simultaneous compounds and have lees restrictions regarding position and combination with other categories.

Main observations

SEQUENTIAL COMPOUNDS

• Sequential compounds usually involve a CORE sign. • There are no compounds combined by a two handed sign (as member), and a one handed sign (a second member).

SIMULTANEOUS COMPOUNDS

• Both members of simultaneous compounds are always classifier signs.


Xuan Wu
email: xuan.wu@ensam.eu

Virginie Goepp
email: virginie.goepp@insa-strasbourg.fr

Ali Siadat
email: ali.siadat@ensam.eu

THE INTEGRATIVE LINK BETWEEN CYBER PHYSICAL PRODUCTION SYSTEMS AND ENTERPRISE INFORMATION SYSTEMS

Keywords: Cyber Physical Production Systems, Enterprise Information Systems, Industrial Engineering, Meta Model, 5C Architecture

In the era of industry 4.0, an extremely promising technology is the Cyber Physical System (CPS), which makes the fusion of the physical and the virtual world. The application of CPS in the production environment leads to the development of Cyber Physical Production Systems (CPPSs). CPPSs hold great potential to make production systems become intelligent, resilient and self-adaptive. The number of articles on CPPSs has been growing very fast, but largely detached from industry practices. One of the main obstacles is to make the integrative link between CPPSs and Enterprise Information Systems (EISs). Therefore, the purpose of this paper is to propose a meta model to formalize this link. First, the definitions of CPPSs and EISs are given, and the meaning of the integrative link between CPPSs and EISs is illustrated from an informational dimension, a technological dimension and an organizational dimension. Then, after analyzing the existing studies of linking CPPSs and EISs in the literature, we can conclude that none of the research conceptualizes the integrative link between CPPSs and EISs. Therefore, at last, a meta model that conceptualizes this link is proposed. The meta model describes the main classes that constitute CPPSs and EISs, and clearly highlights the links between these classes. It is a first step to conceptualize the integrative link between CPPSs and EISs, although in a coarse way.

INTRODUCTION

The manufacturing industry is facing well-known trends, such as highly customized products, increasing product complexity and shorter product lifecycles. To succeed in, Industry 4.0 and smart factory appear on the scene, as the most widespread industrial paradigms. Industry 4.0 is an umbrella term comprising an array of different high-tech technologies and is characterized by the Cyber-Physical System (CPS) in the context of industrial production [START_REF] Longo | Smart operators in industry 4.0: A humancentered approach to enhance operators' capabilities and competencies within the new smart factory context[END_REF]. Smart factory shares the attributes of CPS for monitoring physical processes by creating a virtual copy of the physical world and making decentralized decisions [START_REF] Lee | A cyber-physical systems architecture for industry 4.0-based manufacturing systems[END_REF]. Therefore, we can note that the common enabler behind Industry 4.0 and smart factory is essentially CPS. The concept of CPS can be applied to different disciplines, resulting in multiple definitions of what the CPS is. The core idea of CPS is the interaction between physical components and software components in intertwined networks, thereby fusing the real and the virtual world. Researches and applications of CPS have become active in numerous fields like transportation, healthcare, smart home, civil infrastructure and so on [START_REF] Giraldo | Security and privacy in cyberphysical systems: A survey of surveys[END_REF]. In this paper, we focus on the specific application of CPS in the production domains, resulting in so-called Cyber-Physical Production Systems (CPPSs).

The concept of CPPSs

Since the notion of CPPSs is relatively new, a conclusive definition has not been agreed upon yet. Most of the researchers just simply described the concept of CPPSs as the application of CPSs in the field of the production environment.

The most cited, detailed definition of CPPSs was given by Monostori et al. [START_REF] Monostori | Cyber-physical systems in manufacturing[END_REF]: "CPPSs consist of autonomous and cooperative elements and sub-systems that are getting into connection with each other in situation dependent ways, on and across all levels of production, from processes through machines up to production and logistics networks". In this definition, we can conclude several points: (i) CPPSs are systems of systems, more than just isolated systems because of complex interactions among them; (ii) These systems consist of autonomous and cooperative elements and can be connected or decoupled depend on different situation, which means subsystems are independent and reconfigurable; (iii) The connection between systems impacts all levels of production lifecycle from manufacturing to logistics. However, in this definition, two important concepts are missing: knowledge management and human resources. On the one hand, knowledge is key for decision making and an automated continuous improvement of CPPSs' operations. On the other hand, although CPPSs can work in an automatic way, humans should have a central and crucial role instead of being replaced by technologies. Humans are the only ones who can govern the systems, address anomalous situations and provide flexible solutions in case of need.

The following definition, suggested by Ribeiro [START_REF] Ribeiro | Cyber-physical production systems' design challenges[END_REF], emphasized these missing points: "A CPPS is a composition of human resources, production equipment and aggregated products towards which it establishes one or several cyber-physically formulated interaction interfaces. These interfaces are used for monitoring and control of the CPPS operations as well as to tap into the knowledge generated both by the human resources, and the equipment, during the production process as well as knowledge generated by its aggregated products throughout their life-cycle." These two definitions can complement each other to form a clear synthesis of the various aspects of this large concept.

The notion of CPPSs is very wide and brings many different fields of research together. Its development can be categorized into three distinct communities in parallel: (i) The industrial engineering community, predominantly is interested in CPPSs engineering and implementation approaches. They adopt fundamental systems engineering concepts and methods; (ii) The computer science community, mainly concentrates on information technologies required by CPPS and development methods of software systems; (iii) The electrical engineering community, mainly focuses on hardware in CPPSs, such as sensors. In this paper, we study CPPSs in view of industrial engineering.

Difficulties in industrial practices

There has been a great deal of efforts toward CPPSs in literature, however, the application of CPPSs in industrial practices is still at its infancy.

Orzes et al. [START_REF] Orzes | Industry 4.0 Implementation Barriers in Small and Medium Sized Enterprises: A Focus Group Study[END_REF] conducted focus group studies in four countries (USA, Italy, Austria, and Thailand) to investigate the main difficulties faced by small and medium-sized enterprises in Industry 4.0 implementation. A set of obstacles were identified and were classified into six categories: economic-financial, cultural, competencies/resources, technical, legal, and implementation process. Among these categories, the technical one mainly concerns the lack of support by Enterprise Information Systems (EISs). EISs rely on software such as Manufacturing Execution Systems (MES) and Enterprise Resource Planning (ERP) for implementing business processes, information flows, data visualization and analysis. This is consistent with the studies in [START_REF] Vogel-Heuser | Current status of software development in industrial practice: Key results of a large-scale questionnaire[END_REF] and [START_REF] Telukdarie | Enterprise Definition for Industry 4.0[END_REF], which showed that the implementation of MES and ERP in Industry 4.0 context was limited. Vogel-Heuser and Sarda-Espinosa [START_REF] Vogel-Heuser | Current status of software development in industrial practice: Key results of a large-scale questionnaire[END_REF] gave a survey to 16 German companies in the areas of machine and plant manufacturing which showed that the involvement of MES was only 4%. Telukdarie and Sishi [START_REF] Telukdarie | Enterprise Definition for Industry 4.0[END_REF] conducted a thorough analysis from respective vendors (e.g. Siemens, Rockwell, Honeywell), which showed that MES and ERP had a lack of support on Industry 4.0 paradigms, such as big data, Augmented Reality (AR), cloud, smart device and integrated supply chain.

From the results presented in these surveys, it is clear that the Industry 4.0 paradigm is a difficult conundrum in practice. One of the major obstacles lies in the integrative link with EISs. To promote wide-spread industry adoption, it will be necessary to study the integrative link between EISs and CPPSs.

The concept of EISs

EISs are Information Systems (ISs) in the enterprise context. The benefits of EISs are increased efficiency and productivity, reduced time and cost, zero errors and optimized inventory [START_REF] Manavalan | A review of Internet of Things (IoT) embedded sustainable supply chain for industry 4.0 requirements[END_REF]. EISs have key roles in an organization to support the execution of managerial, operational, and executive-level processes. Generally, a common definition of EISs is the focus on its technological dimension, in other words, it concerns the software on which EISs rely. As defined by Rashid, Hossain and Patrick [START_REF] Rashid | The evolution of ERP systems: A historical perspective[END_REF], "EISs are software systems for business management, encompassing modules supporting organizational functional areas such as planning, manufacturing, sales, marketing, distribution, accounting, financial, human resources management, project management, inventory management, maintenance, transportation and e-business". But according to Reix et al. [START_REF] Reix | Information systems and management, 7 th Edition[END_REF], ISs are not only software, but can be defined as multidimensional information processing objects, including 3 main dimensions: (1) An informational dimension. ISs are the representations of the environment through a set of data. (2) A technological dimension. ISs are not only computer systems, but any systems that make it possible to carry out the processes of collecting, storing and processing information. The technical means would therefore be concerned to accomplish the tasks related to these different processes. The main bases are hardware (computers) and software. (3) An organizational dimension. The majority of ISs operate within organizations, therefore they can be analyzed from the functional and structural perspectives. From the functional perspective, ISs should support business processes and decision making processes. From the structural perspective, the execution of processes requires actors and technological resources. As such, EISs also include these three dimensions.

The integrative link between CPPSs and EISs

According to the concept of EISs, the integrative link between CPPSs and EISs can be considered through the three dimensions of EISs: (1) An informational link, which deals with exchange of data and information between EISs software and CPPSs, (2) A technological link, which uses the information technologies provided by EISs to achieve processes of collecting, storing and processing data in CPPSs, and (3) An organizational link, which deals with the way CPPSs impact business processes and decision making processes supported by EISs.

The integrative link has long been, and often still is, confused with its technological link due to the bias of the computer science community. While it is true the link in its broad sense is surely first of all a technological one which leverages the latest information technologies to combine the digital and physical world, more importantly is an organizational link to better support the decision making processes and business processes. Therefore, the integrative link is the integration of all elements including data, information technologies (IT), people and business processes to achieve the optimal fulfilment of the business mission. This link is not a main research focus in the EISs field, because, as far as we know, in this field the focus is mainly on EISs design and engineering methods, enterprise architectures, enterprise integration and enterprise interoperability approaches. For example, Avila, Goepp and Kiefer [START_REF] Avila | Addressing alignment concerns into the design of domain-specific information systems[END_REF] presented an extended-strategic alignment model for the design and development of domain-specific EISs. Mamoghli, Goepp and Botta-Genoulaz [START_REF] Mamoghli | Aligning ERP systems with companies' real needs: an 'Operational Model Based'method[END_REF] proposed an 'Operational Model Based' method to address alignment between the processes desired by the company and the ERP system's standard processes.

However, since the term CPPSs describes primarily information and communication technologies (ICT) driven changes in production systems, the informational and technological dimension link are already embedded in the CPPSs research area. Therefore, we can get the way the informational and technological links are treated in literature of CPPSs. Motivated by this need, section II introduces existing studies of linking CPPSs and EISs in the literature and analyses the challenge of linking them. Then section III proposes a meta model to conceptualize the integrative link between CPPSs and EISs. Section V concludes this paper.

EXISTING STUDIES AND CHALLENGES OF LINKING CPPS AND EIS

Existing studies of linking CPPSs and EISs in the literature

Lee, Bagheri and Kao [START_REF] Lee | A cyber-physical systems architecture for industry 4.0-based manufacturing systems[END_REF] proposed a 5C architecture for implementing CPSs, which provided a step-by-step guideline from the initial data acquisition to the final value creation, and it can be extended to CPPSs. As shown in Figure 1, it consists of five levels: smart connection, data-to-information conversion, cyber, cognition and configuration level. The smart connection level (level I) represents the physical space, levels II-IV represents the ''pure'' cyber space, while the configuration level (level V) realizes the feedback from the cyber space to physical space. We can use the 5C architecture to get the way the informational and technological links between CPPSs and EISs are treated in the literature of CPPSs. As we described in subsection 1.4, the informational link achieves the exchange of data and information between CPPSs and EISs software. The connection level acquires data from machines and their components by sensors or controllers or EISs software such as ERP and MES [START_REF] Silva | Universal parser for wireless sensor networks in industrial cyber physical production systems[END_REF]. The data-to-information conversion level infers meaningful information from the CIE49 Proceedings, October 18-21, 2019, Beihang University

[PaperNr]-5 large amount of data and show it in the EIS software. The cyber level acts as a central information hub. Information is being pushed to EIS software from every source and compiled to establish a cyber space [START_REF] Lu | Resource virtualization: A core technology for developing cyberphysical production systems[END_REF]. Therefore, we can found that the informational link was implemented from the connection level to the cyber level.

As we described in subsection 1.4, the technological link uses the information technologies provided by EISs to achieve processes of collecting, storing and processing data in CPPSs. In the connection level, considering various types of data, data acquisition technologies are required where specific protocols such as MTConnect are effectively useful. For example, Urbina et al. [START_REF] Urbina | Cyber-physical production system gateway based on a programmable SoC platform[END_REF] established communication with different elements by integrating different interfaces (e.g. Profinet), and connections to sensors (e.g. Modbus series). In the data-to-information conversion level, data processing technologies [START_REF] Lee | Implementation of cyber-physical production systems for quality prediction and operation control in metal casting[END_REF] are required. In the cyber level, having massive information gathered, information analyzing technologies have to be used to extract additional information. With the current trend of increased connectivity to external networks, CPPSs are increasingly targeted by cyber-attacks. There should be technologies to monitor and detect abnormal behaviors [START_REF] Sándor | Cross-layer anomaly detection in industrial cyber-physical systems[END_REF]. In the cognition level, proper presentation technologies of the acquired knowledge to expert users are required for better decision making, as in [START_REF] Pujo | Wireless Holon Network for job shop isoarchic control[END_REF]. Therefore, we can found that the technological link was implemented from the connection level to the cognition level.

The challenge of linking CPPSs and EISs

As we described before, we can found that there have been a number of studies on the informational link and technological link between CPPSs and EISs. For the informational link, the research focus and challenge is to build a digital twin, which is the virtualization of physical entities of CPPSs. Research on the technological link mainly deals with the technical issues of connecting systems, devices, applications and services, including aspects such as communication protocols, interconnection services, specific data formats, data integration and middleware, accessibility and security, and information presentation. The challenges include data acquisition, big data processing and cyber security technologies.

The informational link and technological link have been addressed in the literature, but the organizational link has not, as far as we know. However, the organizational link, which deals with the people involved, the way to process data in EISs, is the most complex and challenging for CPPSs. The challenge is bidirectional, one is what useful data should be retrieved from CPPSs, the other is what impacts the decision made in the EISs will have on CPPSs. We can retrieve all the data thanks to the ICT capabilities of CPPSs, but it makes no sense as we should only retrieve the useful data which can support the business processes and contribute to the overall performance of the organization. It means we should provide the right data to the right person at the right time to make the right decision, which is implemented in the cognition level. Then the configuration level can apply the corrective decisions to have a feedback and make the adjustment in the physical space of CPPSs. If we want CPPSs to work sustainably, we have to implement the organizational link to better support the business processes and decision making processes.

A META MODEL

As previously discussed, none of the research within the CPPSs field addresses the organizational link and conceptualizes the three levels of links between CPPSs and EISs. In order to achieve a common understanding of these links, this section proposes a meta model, serving as a reference to show the interrelationship between the classes in the CPPSs and EISs fields, using an UML class diagram. So, we design the meta model, as shown in

Classes in the CPPSs field

In the CPPSs field, we can extract the classes and their relationships according to the 5C architecture as we described in Section 2.1. To set up these classes, we extract a set of keynouns (in bold) to become classes in the meta-model, from the description of each level of the 5C architecture. For example, the target of the connection level is "acquiring data from machines and their components is the first step and the data might be directly measured by sensors or obtained from controllers or EIS software". Form this sentence we get the following classes for our meta-model: data, machine, component, sensor, controller and EIS software, the results of this analysis for the five levels of the 5C architecture is as follows. In the cyber level, two classes can be extracted: Information Hub and Information Analysing Technology. The class Information Hub is made up of Information. Therefore, there are aggregate relationships between them. The Information Analysing Technology are need in the information hub. There are dependency relationships between them.

In the Cognition level, four classes can be extracted: Knowledge, Presentation Interface, Expert User and Decision. This level generates a thorough knowledge according to aggregated information. There are multiplicity associations between the class Knowledge and the class Information. Expert users get the Knowledge through presentation interfaces and then make decisions. Therefore, there are dependency relationships between the class Knowledge, the class Presentation Interface and the class Expert User, and directed association relationships between the class Expert User and the class Decision.

The Configuration level is the feedback from a cyber space to a physical space, so there are no new classes in this level. The class Decision will control the class Production System in the physical space.

Classes in the EISs field

In the EISs field, we can extract the classes and their relationships according to the enterprise modelling standards ISO 19439 [START_REF]Enterprise Integration-Framework for Enterprise Modelling[END_REF] and ISO 19440 [START_REF]Enterprise Integration-Constructs for Enterprise Modelling[END_REF]. The ISO 19439 serves as a common basis for modelling enterprises and provides four enterprise model views to describe the various aspects of the enterprise, including the information view, the resource view, the function view and the organization view. According to the definition of EISs described in Section 1.3, the four enterprise model views can be partially mapped to the three dimensions of EISs as follows.

(1) Information view, which represents the information used in an enterprise, can be partially mapped to the informational dimension of EISs;

(2) Resource view, which represents the enterprise assets (e.g. human and technological components) that are needed for carrying out the enterprise operations, can be partially mapped to the technological dimension of EISs;

(3) Function view, which represents the business processes in an enterprise, can be partially mapped to the functional perspective of the organizational dimension of EISs;

(4) Organization view, which represents the organization, organizational relationships and the decision-making responsibilities in an enterprise, can be partially mapped to the structural perspective of the organizational dimension of EISs.

The ISO 19440 defines a set of enterprise modelling constructs conforming to the four enterprise model views of ISO 19439 as follows.

• Information view: Enterprise Object, Enterprise Object View, Order, Product;

• Resource view: Resource, Functional Entity, Capability, Operational Role;

• Function view: Domain, Business Processes, Enterprise Activity, Event;

• Organization view: Person Profile, Organizational Role, Organization Unit, Decision Center.

[PaperNr]-8 Among these constructs, we can select the constructs that can represent EISs as the classes of the EISs field of our meta-model.

In the information view of enterprise modelling, the corresponding four constructs are all used to represent the information used in an enterprise, not in the EISs, so we will not use them to represent the informational dimension of EISs. We use the class "Data" and the class "Information" that already exist in the CPPSs.

In the resource view of enterprise modelling, we use the constructs "Resource", "Functional Entity" and "Capability" to represent the technological dimension of EISs. We will not use the construct "Operational Profile" which represents the human skills and responsibilities that are not relevant to the technical part of EISs. So, the construct "Resource" can describe the capabilities all material and informational aids in the EIS, including the software and hardware. The construct "Functional Entity" can represent a special type of resource which is a self-sufficient part of the manufacturing system, including all need ICT capabilities. The construct "Capability" can describe the functionality which is needed to support the execution of the task to be performed by an enterprise activity, and to identify constraints determined by the things to be processed (such as security aspects, data processing/storing capacity, etc.).

In the function view of enterprise modelling, we use the constructs "Domain", "Business Processes" and "Enterprise Activity" to represent the organizational dimension of EISs. We will not use the construct "Event" which represents the initiation of a state change in the enterprise that is not relevant to EISs. So, the construct "Domain" can represent the boundary and the content of EISs. The relations between inputs and outputs of the domain identify the required functionalities -the business processes of the domain. The construct "Business Process" can represent a partially ordered set of business processes and enterprise activities, or both, that can be executed to realize given objectives of an enterprise to achieve some desired end-result. The constructs "Enterprise Activity" are the lowest level of process functionality that is needed to realize a basic task within a business process.

In the organization view of enterprise modelling, we use the constructs "Person Profile" to represent the organizational dimension of EISs because it can describe the human skills available to serve the assigned operational tasks. We will not use the constructs "Organizational Role", "Organization Unit" and "Decision Center" because they all describe the organizational relationships in the enterprise which are not relevant to the EISs.

In conclusion, according to the enterprise modelling standards, we extract three classes to represent the technological dimension of EISs, including Resource, Functional Entity and Capability, and four classes to represent the organisational dimension of EISs, including Domain, Business process, Enterprise Activity and Person Profile. For the informational dimension of EISs, we will use the class Data and Information that already exist in CPPSs.

Link between CPPSs and EISs

After identifying and defining all the classes in the CPPSs and EISs fields, we describe the integrative link between CPPSs and EISs as the relations between the classes belonging to the three dimension of EISs and CPPSs, so they can be described as follows.

In the informational link, the EISs and CPPSs share the same classes Data and Information, these two classes have relationships with other classes from the connection level to the cyber level in the CPPSs as we already described in Section 3.1. These relationships show that data and information can be obtained and shared between CPPSs and EISs software. Processing Technology and Information Analysing Technology in the CPPSs field. These relationships show that EISs can provide the software, hardware and ICT capabilities to enable CPPSs to collect, store and process data and information.

In the organizational link, the decision made in the cognition level of CPPSs will have impacts on business processes and improved business processes will result in material entities (such as industrial products), or the information entities (such data), or newly designed processes. Therefore, the class Decision has directed association with the class Business Process and the class Business Process has directed association with the classes Production system and Data. The person profile can be assigned to more than one person and conversely a person can fulfil more than one-person profile. Therefore, the class Expert User in the cognition level of CPPSs have multiplicity associations with the class Person Profile in the EISs.

According to the above description, the meta model comprehensively describes all the essential classes within the CPPSs and EISs field, and clearly conceptualize the integrative link between CPPSs and the three dimensions of EISs using red lines in Figure 2.

CONCLUSION

CPPSs can be considered as an extremely important step in the development of production systems. There has been a great deal of efforts toward CPPSs in literature. However, the application of CPPSs in industrial practices is still at its infancy. To promote wide-spread industry adoption, our aim is to make the integrative link between EISs and CPPSs. Key highlights from this study are, [START_REF] Longo | Smart operators in industry 4.0: A humancentered approach to enhance operators' capabilities and competencies within the new smart factory context[END_REF] The definitions of CPPSs and EISs are given, and the meaning of the integrative link between CPPSs and EISs is illustrated.

(2) Through analyzing the existing studies on the integrative link between CPPSs and EISs in the literature, we found the challenge of linking CPPSs and EISs.

(3) A meta model, that conceptualizes the integrative link between CPPSs and EISs, is proposed based on the 5C architecture [START_REF] Lee | A cyber-physical systems architecture for industry 4.0-based manufacturing systems[END_REF] and the enterprise modelling standards ISO 19439 [START_REF]Enterprise Integration-Framework for Enterprise Modelling[END_REF] and ISO 19440 [START_REF]Enterprise Integration-Constructs for Enterprise Modelling[END_REF].

The meta model gives a big picture of the classes that compose CPPSs and EISs. The objective of the model is not to be implemented because it is only a conceptual model that conceptualize the links between the classes in the CPPSs and EISs field in a coarse way. But it is the first step to identify what should be linked to deal with the three dimensions of the integrative link between CPPSs and EISs.

In the future, we will study how to address the organizational link between CPPSs and EISs, including what kind of data to extract from CPPSs, how to structure these data, what useful information can be integrated effectively into EISs, and how these data have impacts on business processes and improve decision-making efficiency.

Figure 1 :

 1 Figure 1: 5C architecture for implementation of CPSs [2]

Figure 2 .Figure 2 :

 22 Figure 2: A meta model for the integrative link between CPPSs and EISs

  In the Connection level, thirteen classes can be extracted: Data, Data Source, Component, Machine, Production System, Sensor, Controller, EIS software, Protocol, Data Acquisition Technology, Data Storage Technology, Data Transferring Technology and Central Server. The class Data Source includes the class Sensor, Controller and EIS Software. Therefore, there are inheritance relationships between these four classes. A Component has at least a Sensor, a Machine has at least a Controller and a Production System has at least an EIS software. Therefore, there are directed association relationships between these six classes. The class Production System is made up of one or more Machines, the class Machine is made up of one or more Components. Therefore, there are aggregate relationships between these three classes. The Data can be acquired from the Data Source and transfer to the Central Server. There are directed association relationships between these three classes. In this process, the Protocol, Data Acquisition Technology, Data Storage [PaperNr]-7 Technology and Data Transferring Technology are used. Therefore, there are dependency relationships between these four classes and the class Data. In the Data-To-Information Conversion level, two classes can be extracted: Information and Data Processing Technology. The central server needs to use data processing technology to have meaningful information. Therefore, there are dependency relationships between the class Central Server and the class Data Processing Technology, and the directed association relationships between the class Central Server and the class Information, and association relationships between the class Data and the class Information.

  In the technological link, the class Resource in the EISs field includes the software and hardware, therefore it has inheritance relationships with the classes EIS Software, Central Server and Presentation Interface. The class Functional Entity in the EIS field describes ICT capabilities, therefore, it has inheritance relationships with the classes Protocol, Data Acquisition Technology, Data Storage Technology, Data Transferring Technological, Data [PaperNr]-9