Abstract

The increased demand for textile products leads to an increase in the quantity of wastewater discharged. It becomes indeed one of the most critical health and environmental problems in the world. The main challenge, therefore, is to develop innovative techniques for treating this wastewater with low production costs and better efficiency. The major objective of this work was to investigate the efficiency of the coupling of the coagulation–flocculation and the anodic oxidation processes on the platinum electrode in the removal of organic, mineral, and microbial pollution contained in textile effluents. A series of experiments is carried out on samples prepared in the laboratory, in which the textile effluent was mixed with a secondary effluent from an urban wastewater treatment plant. The treatment consists of two steps: a coagulation–flocculation process using aluminum salts as a coagulant and an anodic oxidation on the platinum electrode using photovoltaic panels for the production of electric current. The treatment at optimized conditions reveals that the coupling of the two processes made it possible to achieve satisfactory results. The abatement rates were 95.97% for the turbidity, 90% for COD, 100% for BOD, 100% for , 53.6% for , and 100% for . The coupling of the two processes ensured the complete elimination of fecal germs. Thanks to the satisfactory results, the obtained permeate can be reused in the dyeing process in the textile industry.

HIGHLIGHTS

  • Coupling of the coagulation–flocculation process with anodic oxidation allowed removing contaminants.

  • The coupling of the two processes ensured the complete elimination of fecal germs.

  • The total elimination of organic, nitrogen, and phosphorus pollution was obtained.

  • The treated water can be reused for different purposes.

  • Mixing urban wastewater with the textile effluent improves the pollutant removal rate.

INTRODUCTION

Worldwide environmental issues related to the textile industry are typically those associated with water pollution caused by the discharge of wastewater effluent since it contains toxic substances. In addition, the composition of wastewater from dyeing and textile processes varies considerably from day to day and even from hour to hour, depending on dye, fabric, and concentration of fixing compounds that are added (Kim et al. 2004). This wastewater is very stable in the environment and resistant to oxidation and biodegradation (Croce et al. 2017). It is considered a source of esthetic pollution and it permits the disturbance of the aquatic ecosystem. Photosynthesis and reduced oxygen solubility result from the discharge of wastewater made up of dye compounds, even at low levels (Rahmani et al. 2015). However, textile mills are not designed to eliminate all kinds of pollutants such as inorganic and organic substances, which should be included in the treatment priorities. Furthermore, leachate has high values of biological oxygen demand (BOD), chemical oxygen demand (COD) and, because of its toxic potential (Anvari et al. 2014; Garcia-Segura et al. 2018), can pose a problem for the environment (Clement et al. 1997; James & Stack 1997). The treatment of textile effluents is a major concern since the rejection of such wastewater drastically decreases oxygen concentration in the aquatic ecosystems.

Apart from the unsightly appearance, the coloring agents are able to interfere with the transmission of light in the water, thus blocking the photosynthesis of aquatic plants (Mansour et al. 2011). The works on these azo dyes have shown that these chemical compounds have carcinogenic effects on humans and animals (Combes & Haveland-Smith 1982; IARC 1982; Medvedev et al. 1988; Percy et al. 1989; Brown & Devito 1993; DEPA 2000; Tsuda et al. 2000; Chen 2006). These authors unanimously agreed on the gravity of these polluted waters, which requires cleaning them. Depending on the characteristics of the effluents, it will be necessary to resort to new methods such as coagulation–flocculation (C-F) coupling with the advanced oxidation process on the platinum electrode.

In this study, C-F has been chosen, for its simplicity to remove turbidity and reduce the COD value of dye wastewater. El-Gohary & Tawfik (2009) confirmed this idea. The cycle of treatments involved coagulation/flocculation/decantation by using aluminum sulfate as a coagulant. This last neutralizes the charge of the particles, allowing them to agglomerate, and settle at the bottom of the tank (Verma et al. 2012). This mechanism occurs because the coagulants form monomeric and polymeric species in contact with water, with metallic hydroxides (Alkarkhi et al. 2013). Depending on the volume of water treatment, chemical coagulation can be very expensive. One of the possible problems is the difficulty of being able to reduce the solubility enough so that the components can form flocculants to be removed from wastewater (Verma et al. 2012). Consequently, according to Nabi et al. (2007) and Georgiou et al. (2003), many attempts were made to combine treatment methods for better and improved to treat wastewater. C-F combines almost all types of treatment methods currently available to treat wastewater (Butler et al. 2016).

On the other hand, with the ever-increasing level of drinking water supply and strict environmental regulations regarding the discharge of wastewater, electrochemical technologies have regained their importance worldwide over the past two decades (Chen & Hung 2007). Subsequently, a great deal of research has been devoted to this goal, highlighting the prominent role of a special class of oxidation techniques defined as advanced oxidation processes (AOPs), which generally operate at or near ambient temperature and pressure (Aieta et al. 1988). These AOPs have been applied in several sectors, such as the treatment of industrial wastewater (Martínez-Huitle & Ferro 2006). Unlike conventional methods, anodic oxidation does not need any additional processes and chemicals, and the system does not lead to the formation of byproducts (Rahmani et al. 2015). The AOPs rely on the production of highly reactive hydroxyl radicals (OH). These strongest oxidants are highly oxidizing and nonselective in nature (Asghar et al. 2015), and they are able to decompose mainly organic matter (Farhataziz & Ross 1977; Hoigné & Bader 1983) up to their mineralization (Sirés et al. 2014; Verma & Samanta 2018). These compounds react with the double bonds –C–C– and attack the aromatic nuclei, the major components of the refractory compounds (Gogate & Pandit 2004).

The hydroxyl radicals are produced from a hemolytic rupture of a covalent bond, that is to say, that the two electrons involved during this bond share one electron for each atom (Millet 1992a, 1992b). This characteristic gives it a strongly polar character, and consequently, it is highly reactive with respect to numerous organic (aromatic and aliphatic), inorganic, and bacterial compounds (Zaviska et al. 2009). The results obtained by Cong et al. (2008) confirmed that this hydroxyl radical is generated under neutral, basic, and acid conditions (reactions 1 and 2).
formula
(1)
formula
(2)

MATERIALS AND METHODS

The experimental study lasted 4 months, from November 2018 to February 2019. The experiments were carried out in the Laboratory of Applied Hydro-Science of the Higher Institute of Sciences and Techniques of Waters (University of Gabès, Tunisia).

In order to determine the best method of treating textile wastewater to remove organic, mineral, and microbial pollution, the effluent has been treated successively by the C-F and the anodic oxidation (AO) processes on the platinum electrode.

Wastewater characteristics

In order to reduce the high load of pollutants in this industrial sewage effluent, the treatment was carried out using a textile effluent (TE) diluted 20 times with a secondary effluent from the wastewater treatment plant of the city of Gabès_Metouia (southeast of Tunisia) in the proportion of 5 and 95%, respectively,

The main physicochemical and microbiological characteristics of this mixed solution (M-5% solution) used during the experiments are presented in Table 1.

Table 1

Physicochemical and microbiological characteristics of the M-5% solution

ParametersValues
pH 7.2 
EC (mS/cm) 4.8 
Temperature (°C) 19.9 
Turbidity (NTU) 35 
BOD (mg O2/L) 6.4 
COD (mg O2/L) 239.9 
Dissolved oxygen (mg/L) 7.76 
(mg/L) 39.2 
(mg/L) 15.54 
(mg/L) 0.027 
TC (colonies/mL) 150 
FC (colonies/mL) 43 
FS (colonies/mL) 64 
ParametersValues
pH 7.2 
EC (mS/cm) 4.8 
Temperature (°C) 19.9 
Turbidity (NTU) 35 
BOD (mg O2/L) 6.4 
COD (mg O2/L) 239.9 
Dissolved oxygen (mg/L) 7.76 
(mg/L) 39.2 
(mg/L) 15.54 
(mg/L) 0.027 
TC (colonies/mL) 150 
FC (colonies/mL) 43 
FS (colonies/mL) 64 

C-F experiments

Several studies have shown that the removal efficiency of organic compounds by the aluminum salt is improved by optimizing the pH and the dose of coagulant used (Lefebvre & Legube 1990; Al-Malack et al. 1999). The optimal pH of the C-F process is between 6 and 7.4 for aluminum (Bratby 1980; Gregory 2005). In this study, the pH was in this optimal range. Practically, the optimal dose of coagulant can be determined by a laboratory test, known as the ‘Jar test’ (Lounnas 2009).

The C-F experiments using inorganic coagulants, namely aluminum sulfate (Al2SO4)3 (18H2O), were carried out by the standard Jar test apparatus consisting of a flocculator with six agitators, to determine optimum operating conditions.

In the first step, the Jar test experiments were carried out on the mixed solutions, in different graduated glass beakers. The coagulant (aluminum) was prepared in solutions at 5 g/L concentration, and the flocculant (PolyDiAllyl Diméthyl Ammonium Chlorure ‘polyDADMAC’ at a concentration of 1.09 g/L) was tested. A different dose of coagulants was added separately and quickly mixed at 120 rpm for 2 min. Then, the flocculant was added, and the speed was reduced to 40 rpm for 20 min. In the second step, the particles are left to settle for about 120 min. After decantation, turbidity, COD, BOD, , , , and fecal germs were measured in the supernatant to determine the most adequate quantity of coagulant for the abatement of this pollution.

AOP on the platinum electrode

In particular, elegant solutions for cleaning up environmental pollutants have been provided by the electrochemical methods. These processes are significantly efficient, versatile, and environmentally friendly (Vasudevan & Oturan 2013; Sirés et al. 2014). In these processes, the oxidation of pollutants occurs at the surface of the anode where the hydroxyl radicals are formed, in the presence of an aqueous electrolytic solution (Verma & Samanta 2018).

In order to study the mode of operation of the AOP and to determine its purification performance, an experimental study was carried out using two electrodes: a platinum anode and a steel cathode (Figure 1). The platinum electrode used in this treatment has the physical properties, as shown in Table 2. Its oxidation potential is equal to 1.18 (V/SHE) (Daniel 2007). The steel cathode used in this work is characterized by thickness: 2 mm, width: 2.5 cm, and length: 5 cm. The characteristics of the panels used, which are of the ‘polycrystalline silicon’ type, are illustrated in Table 3.

Table 2

Physical properties of the platinum

Chemical symbol Pt 
Atomic number 78 
Thickness 0.5 mm 
Width 2 cm 
Length 2 cm 
Density 21.45 g/cm3 
Chemical symbol Pt 
Atomic number 78 
Thickness 0.5 mm 
Width 2 cm 
Length 2 cm 
Density 21.45 g/cm3 
Table 3

The characteristics of the photovoltaic panels

Model 001 
Construction material Polycrystalline silicon 
Maximum power (Pmax2 W 
Voltage at maximum power (Vmp8 V 
Current at maximum power (Imp0.25 A 
Open-circuit voltage (Voc9.2 V 
Short-circuit current (Isc0.263 A 
Maximum system voltage 500 V 
Size 170 × 130 × 4 mm 
Model 001 
Construction material Polycrystalline silicon 
Maximum power (Pmax2 W 
Voltage at maximum power (Vmp8 V 
Current at maximum power (Imp0.25 A 
Open-circuit voltage (Voc9.2 V 
Short-circuit current (Isc0.263 A 
Maximum system voltage 500 V 
Size 170 × 130 × 4 mm 
Figure 1

Anodic oxidation experimental device on platinum.

Figure 1

Anodic oxidation experimental device on platinum.

The part of a centimeter of the cathode was placed vertically in the solution while the anode was completely immersed, in order to guarantee that the submerged surface is equal, of which the production of electrons at the level of two electrodes is proportional. The current applied between these two electrodes was imposed by a series of photovoltaic panels. The influence of electric intensity (250, 500, 750, and 1,000 mA) and electrolysis time were investigated. The solutions were homogenized using a magnetic stirrer at a moderate speed. A volume of 1 liter of mixed solution was treated.

C-F treatment combined with the AOP on the platinum electrode

The optimal conditions previously obtained where the applied C-F was combined with the AOP in the reactor previously described in order to improve the dye wastewater quality. Firstly, an optimal dose (80 mg/L) of coagulant (Al2 (SO4)3) was added to the dulled solution. Secondly, after settling, the supernatant was recovered to be treated for 2 h by the AO with an intensity of 1,000 mA brought by the photovoltaic panels. Finally, to evaluate the treatment efficiency of the diluted effluent, the following parameters are studied: turbidity, COD, BOD, ammonia, nitrogen, orthophosphates, and fecal germs.

RESULTS AND DISCUSSION

Following pH and electrical conductivity

The results obtained showed a slight decrease in pH and electrical conductivity (EC) (Table 4). The study published by Sefraoui (2013) confirmed this decrease in the pH value after treatment with aluminum which is always less than or equal to the initial value, since it is strongly related to the concentrations injected with the products (coagulant and flocculant) during the C-F process. The results obtained confirm the bibliographic data, concerning the addition of the coagulant that causes the formation of the hydroxide of the metal with the release of a certain acidity (hydrolysis) which explains the decrease in the pH value. This reduction is due to the formation of H3O+ ions and to the reactions that take place at the level of the anode favoring the production of hydroxyl radicals (OH) which attack organic matter by promoting the production of short-chain carboxylic acids that acidify the middle (Gaied et al. 2019).

Table 4

pH and electrical conductivity of the raw and treated effluents

EffluentpHEC
Textile effluent (TE) 7.1 7.6 
Urban effluent (UE) 7.3 4.37 
M-5% 7.3 4.43 
C-F + AO 6.9 4.41 
EffluentpHEC
Textile effluent (TE) 7.1 7.6 
Urban effluent (UE) 7.3 4.37 
M-5% 7.3 4.43 
C-F + AO 6.9 4.41 

Concerning the EC, it remains almost stable, and it records a very slight decrease, which can be explained by the decrease in the dissolved salts in the solution (Total Dissolved Solids).

Removal of turbidity

Figure 2 shows the evolution of turbidity of the raw and analyzed water by the coupling of the two processes. The mixture of the industrial effluent with the urban effluent (UE), in the respective proportion of 5 and 95%, allowed a very important decrease of turbidity with a rate of abatement that was equal to 96.14% compared with the initial value of the TE. This confirms the efficiency and good purification performance of the mixture of the industrial and urban effluents.

Figure 2

The turbidity of raw and analyzed water.

Figure 2

The turbidity of raw and analyzed water.

As shown in Figure 3, the abatement rate was 93.43 and 94.36% for water treated by the C-F and the AOPs on the platinum electrode, respectively. After the treatment of the sample by a coupling of the two treatment processes with the optimal conditions, the rate of abatement was 95.97% compared with the value of the mixed solution (M-5%). This reduction of turbidity depends on both the optimal dose of the coagulant, which has guaranteed the majority removal of colloidal particles and dissolved organic substances, whose main reaction mechanism is the neutralization of the charge of colloids (negatively charged) by cationic hydrolysis products. The duration of the electrolysis and the intensity of the current have significantly improved the purification efficiency by the oxidation of the organic matter expressed in turbidity.

Figure 3

Variation in the rate of turbidity reduction in water treated with C-F, AO, and C-F + AO.

Figure 3

Variation in the rate of turbidity reduction in water treated with C-F, AO, and C-F + AO.

The reaction mechanisms involved are different and complementary. On the one hand, the destruction of organic pollutants takes place by conversion or combustion (Comninellis 1994). During electrochemical conversion, nonbiodegradable organic compounds are partially oxidized to more biodegradable compounds, while during electrochemical combustion, organic pollutants are completely degraded in the form of CO2 and H2O (Grimm et al. 1998). On the other hand, the hydrolysis of alum makes it possible to form hydroxyaluminous radicals (monomers) which, in turn, form the precipitate Al(OH)3 or polycationic species. These species act on the colloidal particles by compression, neutralization, and adsorption, which make possible the formation of flocs (Lakhdari 2011).

Removal of COD

The evolution of the COD of the raw and analyzed water is illustrated in Figure 4. The results indicated that the COD of the TE was highly fluctuating, with an average of 6,957.19 mg O2/L. This high concentration rate was due to the presence of significant organic pollution that is difficult to biodegrade. After mixing the two effluents, the abatement rate was 96.55%, hence confirms the efficiency and good purification performance of the industrial effluent mixture with the UE in the proportion of 5 and 95%, respectively.

Figure 4

The COD of raw and analyzed water.

Figure 4

The COD of raw and analyzed water.

The results obtained showed a reduction rate of the order of 56.67 and 76.67% after the independent treatment of the solution by the C-F and AO on the platinum electrode, with the optimal conditions, respectively (Figure 5). The coupling of the two processes with the optimal conditions ensured almost complete oxidation of the carbon pollution expressed in terms of COD (90%), which can occur due to the contribution of multiple oxidation mechanisms. According to the studies of Tipping & Backes (1988) and Lefebvre & Legube (1990), the elimination of organic matter by the coagulant is explained by a complexation or exchange of ligand between the monomers, dimers or cationic metallic polymers and the organic matter.

Figure 5

Variation in the rate of COD reduction in water treated with C-F, AO, and C-F + AO.

Figure 5

Variation in the rate of COD reduction in water treated with C-F, AO, and C-F + AO.

Similar results have been found by Rosie et al. (2012), Chiang et al. (1995), Jardak (2015) and Torres et al. (2019) who confirmed that the reduction of COD depends on both the duration of electrolysis and the intensity current. The increase in the intensity of the current has ensured a greater production of hydroxyl radicals (OH) which can instantly oxidize most organic compounds by addition reactions and hydrogen abstraction reactions. This phenomenon corresponds to the oxidation of the water molecule on the surface of the anode to form hydroxyl radicals also known as adsorbed oxygen (reaction 3) (Comninellis 1994).
formula
(3)
In our case, platinum is a nonactive electrode (with a high oxygen overvoltage) whose hydroxyl radicals are weakly bonded to the surface of the anode. This situation allows the hydroxyl radicals to degrade the pollutants into intermediate compounds and to mineralize them in the final stage (reactions 4 and 5) (Jardak 2015).
formula
(4)
formula
(5)

Removal of BOD

In Figure 6, it is observed that there is a total degradation of the BOD. After mixing the TE with the UE, the BOD content was decreased to 6.4 mg O2/L. These results expressed the good purification performance of this mixture with an abatement rate that exceeds 97.71% compared with the initial value of the TE. The treatment of the M-5% solution by the C-F and AO separately with the optimal conditions favored a total reduction in BOD (100%) which confirms the effectiveness of each of these two processes with respect to the elimination of easily biodegradable organic matter (Figure 7). After the coupling of the two processes with the optimal conditions, the BOD has been completely degraded. The almost total disappearance of BOD in the water treated by the coupling could be explained by the good role of the coagulant during the C-F process.

Figure 6

The BOD of raw and analyzed water.

Figure 6

The BOD of raw and analyzed water.

Figure 7

Variation in the rate of BOD reduction in water treated with C-F, AO, and C-F + AO.

Figure 7

Variation in the rate of BOD reduction in water treated with C-F, AO, and C-F + AO.

This excellent yield also comes back to the oxidation power of hydroxyl radicals (OH) which will react instantly with organic components by hydroxylation with a loss of hydrogen atom following a radical mechanism until their total mineralization according to the following reactions:
formula
(6)
formula
(7)
formula
(8)

The attack of these radicals on organic pollutants initiates a radical mechanism, leading to mineralization by three modes of action: electrophilic addition, abstraction of hydrogen atom, and electronic transfer (Guergour 2014).

Removal of

However, as shown in Figure 8, the combination of two processes allowed the complete elimination of ammoniacal nitrogen. The results showed that the mixture provided a significant reduction in the initial value of ammoniacal nitrogen with an abatement rate of 65%. After treating the mixed solution by the two methods independently with the optimal conditions, a total reduction in was noted for each method (Figure 9). The coupling permitted a total oxidation of nitrogen pollution resulting in an almost total reduction of this parameter. Similar results have been found by Binette & Pepin (2003) which confirmed the effectiveness of the C-F process with regard to the reduction of nitrogen pollution.

Figure 8

The of raw and analyzed water.

Figure 8

The of raw and analyzed water.

Figure 9

Variation in the rate of reduction in water treated with C-F, AO, and C-F + AO.

Figure 9

Variation in the rate of reduction in water treated with C-F, AO, and C-F + AO.

Szpyrkowicz et al. (2005) showed that the elimination of nitrogen is done by electrochemical conversion. Canizares et al. (2005) and Amor (2018) confirmed that the elimination of ammoniacal nitrogen is done by a reduction of this oxidized nitrogen whose principle of the electro-conversion of ammoniacal nitrogen is based on the reduction of the latter into gaseous nitrogen at the cathode and the oxidation of water into gaseous oxygen at the anode by applying an electric current through an aqueous solution.

Amor (2018) proved that the ammonia could be completely oxidized and the majority of it has been transformed into nitrogen N2 whose yields were higher in the presence of ammonium chloride, which demonstrated the advantageous contribution of chloride ion to the electro-conversion reaction of ammoniacal nitrogen by increasing the time of electrolysis.

This is likely due to excessive electrolysis of the chloride ion to chlorine gas at the anode (Reaction 9), to the detriment of its reaction with water to generate hypochloric acid (Reaction 10).
formula
(9)
formula
(10)

In other words, the removal efficiency of ammoniacal nitrogen increases with the current density and the Cl concentration due to their strong effect of cooperation with the current density.

Removal of

After mixing the abatement rate of was almost 15.22% relative to the industrial effluent. This decrease could be explained by the denitrification, which consists in eliminating the nitrates present in the water under the action of the microorganisms of the urban wastewater. The coupling of the two processes allowed a rather large decrease in the nitrate content. It was equal to 53.6% relative to the mixing solution (Figure 10). The results obtained showed that the C-F allowed a reduction rate equal to 38.35%, while the reduction rate by AO reached 44.93% (Figure 11).

Figure 10

The of raw and analyzed water.

Figure 10

The of raw and analyzed water.

Figure 11

Variation in the rate of reduction in water treated with C-F, AO, and C-F + AO.

Figure 11

Variation in the rate of reduction in water treated with C-F, AO, and C-F + AO.

This nitrate removal can be explained by the possibility of copper in the secondary effluent. The oxidation of copper ensures the reduction of nitrate anions to nitric oxide, then oxidation by the oxygen of the monoxide to nitrogen dioxide according to the following reaction:
formula
(11)

From Amor (2018), the reduction reaction can be more or less complete and can give rise to intermediate species such as nitrites, nitrates or nitrogen gas. After some electrolysis times, the formation of nitrates begins to decrease. This confirms the fact that this secondary product is a reaction intermediate, the nitrates probably being converted, in turn, into nitrogen gas.

Li et al. (2009) proved that the elimination of nitrate has resulted in cathodic reduction of nitrate and anodic oxidation of ammonia and nitrite byproducts have been achieved.

Removal of

As seen in Figure 12, the concentration is directly eliminated after the treatment by the two processes. The results showed that the abatement rate of in the mixed solution exceeded 99% compared with the initial value of the TE, hence confirms the efficiency and good purification performance of the mixture of the industrial effluent and the UE in the respective proportion of 5 and 95%, respectively. The treatment of the mixed solution by the C-F and AO separately under the optimal conditions also allowed a total reduction of the (100%) which confirms the effectiveness of each of these two processes with respect to the elimination of the phosphate pollution (Figure 13). A similar study by Seghairi et al. (2017) confirmed the effectiveness of the C-F process in the reduction of phosphate pollution. Good performance with respect to the abatement of phosphate pollution could be explained by the precipitation of orthophosphates, according to the following reaction:
formula
(12)
Figure 12

The of raw and analyzed water.

Figure 12

The of raw and analyzed water.

Figure 13

Variation in the rate of reduction in water treated with C-F, AO, and C-F + AO.

Figure 13

Variation in the rate of reduction in water treated with C-F, AO, and C-F + AO.

Removal of pathogenic germs

Experimental results showed that the UE is highly loaded with total coliforms (TC), fecal coliforms (FC), and fecal streptococci (FS). After mixing the two effluents, a reduction in this pathogenic germs content compared with the UE was observed (Figures 1416). This decrease can be explained by the substances found in the industrial effluent and the products (acid, NaOH, H2O2, etc.) used during the textile production chain, which are capable of destroying the pathogenic germs.

Figure 14

The total coliforms of raw and analyzed water.

Figure 14

The total coliforms of raw and analyzed water.

Figure 15

The fecal coliforms of raw and analyzed water.

Figure 15

The fecal coliforms of raw and analyzed water.

Figure 16

The fecal streptococci of raw and analyzed water.

Figure 16

The fecal streptococci of raw and analyzed water.

As shown in Figure 17, the treatment of the M-5% solution by the C-F and AO process separately with the optimal conditions favored a total reduction in TC, FC, and FS (100%). The coupling of these two processes permits the elimination of micropollutants. The works of Gaied et al. (2019) have shown a decrease in the number of bacteria; this may occur not only due to the effect of the current but also due to the generation OH that destroys and kills the microorganisms.

Figure 17

Variation in the rate of TC, FC, and FS reduction in water treated with C-F, AO, and C-F + AO.

Figure 17

Variation in the rate of TC, FC, and FS reduction in water treated with C-F, AO, and C-F + AO.

According to Alem (2015), a bactericidal effect can occur by the formation of oxidants such as hydrogen peroxide or hypochlorous acids obtained during the oxidation of chlorides. Zaviska et al. (2009) mentioned the importance of the electric field between the electrodes, which leads to the destruction of certain strains of bacteria thanks to their power as a bactericidal action. A similar study by Kahoul & Belhachani (2016) has shown that the elimination of pathogenic microorganisms is due to the hydroxyl radicals (OH) which are very reactive with respect to many bacterial compounds.

CONCLUSION

The main objective of this work was to study the elimination of organic, nitrogen, phosphorus and microbial pollution contained in the TE by the coupling of the C-F and the AOPs. The experiments showed that combining these two processes improved the purification of the TE mixed with the secondary effluent. The technique of C-F applied in the laboratory uses a Jar test, which seems to be a durable system of the elimination of pollutants such as turbidity, organic matter, nitrogen, phosphorus, and pathogenic microorganisms. In addition, AO is an effective process that can contribute to the satisfactory removal of organic and mineral matter, and micropollutants contained in the mixed solution. These high yields were obtained thanks to the high oxidation power of the water molecule on the surface of the anode to form hydroxyl radicals, and the current applied between these two electrodes, which was produced by a series of photovoltaic panels.

The coupling of the C-F and the AOPs, by using the optimal treatment conditions, has made it possible to increase the purification performances. The results obtained, after the coupled treatment of the urban wastewater mixture with SARTEX textile industrial wastewater in the proportion of 5 and 95%, respectively, are very satisfactory in terms of removal of turbidity, COD, BOD, , , , TC, FC, and FS. All these parameters are in accordance with the Tunisian standard of rejection. In order to recover these effluents after their purification, they can be reused for domestic, agricultural, or industrial purposes. It may become one of the solutions that can respond to the problems of water scarcity in the world, and the growing needs for this subject.

ACKNOWLEDGEMENT

The authors thank the Research Unit of Applied Hydro-Sciences of Gabès for the technical support.

DATA AVAILABILITY STATEMENT

All relevant data are included in the paper or its Supplementary Information.

REFERENCES

REFERENCES
Aieta
E. M.
,
Reagan
K. M.
,
Lang
J. S.
,
McReynolds
L.
,
Kang
J.-W.
&
Glaze
W. H.
1988
Advanced oxidation processes for treating groundwater contaminated with TCE and PCE: pilot-scale evaluations
.
American Water Works Association
80
(
5
),
64
72
.
https://doi.org/10.1002/j.1551-8833.1988.tb03039.x
.
Alem
S.
2015
Etude comparative entre coagulation floculation et électrocoagulation électroflottation. Memory of Magister, Abderrahmane MIRA Bejaia University, p. 43
.
Alkarkhi
A. F. M.
,
Lim
H. K.
,
Yusup
Y.
,
Teng
T. T.
,
Abu Bakar
M. A.
&
Cheah
K. S.
2013
Treatment of Terasil Red R and Cibacron Red R wastewater using extracted aluminum from red earth: factorial design
.
Journal of Environmental Management
122
,
121
129
.
https://doi.org/10.1016/j.jenvman.2013.03.010
.
Al-Malack
M. H.
,
Abouzaid
N. S.
&
El-Mubarak
A. H.
1999
Coagulation of polymeric wastewater discharged by a chemical factory
.
Water Research
33
(
2
),
521
529
.
https://doi.org/10.1016/s0043-1354(98)00219-x
.
Amor
M.
2018
Étude de l’électro-conversion d'azote ammoniacal par voie électrochimique. Memory of Magister, Québec University, pp. 16–47
.
Anvari
F.
,
Kheirkhah
M.
&
Amraei
R.
2014
Treatment of synthetic textile wastewater by combination of coagulation/flocculation process and electron beam irradiation
.
Journal of Community Health Research
3
(
1
),
31
38
.
http://jhr.ssu.ac.ir/article-1-155-en.html
.
Asghar
A.
,
Abdul Raman
A. A.
&
Wan Daud
W. M. A.
2015
Advanced oxidation processes for in-situ production of hydrogen peroxide/hydroxyl radical for textile wastewater treatment: a review
.
Journal of Cleaner Production
87
,
826
838
.
doi:10.1016/j.jclepro.2014.09.010
.
Binette
A.
&
Pepin
A.
2003
Rapport de synthèse essais de traitabilité des eaux de lixiviation du site projeté d’élimination des matières résiduelles de dépôt rive-nord. Memory of Magister, Montréal University, p. 24
.
Bratby
J.
1980
Coagulation and Flocculation with an Emphasis on Water and Wastewater Treatment. Uplands Press, UK, p. 376
.
Brown
M. A.
&
Devito
S. C.
1993
Predicting azo dye toxicity
.
Critical Reviews in Environmental Science and Technology
12
,
405
414
.
https://doi.org/10.1080/10643389309388453
.
Butler
E.
,
Hung
Y. T.
,
Ahmad
M. A.
&
Fu
Y.-P.
2016
Treatment and management of industrial dye wastewater for water resources protection
.
Natural Resources and Control Processes
,
187
232
.
https://doi.org/10.1007/978-3-319-26800-2_4
.
Canizares
P.
,
Lobato
J.
,
Paz
R.
,
Rodrigo
M.
&
Saez
C.
2005
Electrochemical oxidation of phenolic wastes with boron-doped diamond anodes
.
Water Research
39
(
12
),
2687
2703
.
https://doi.org/10.1016/j.watres.2005.04.042
.
Chen
B. Y.
2006
Toxicity assessment of aromatic amines to Pseudomonas luteola: chemostat pulse technique and dose response analysis
.
Process Biochemistry
41
(
7
),
1529
1538
.
https://doi.org/10.1016/j.procbio.2006.02.014
.
Chen
G.
&
Hung
Y.-T.
2007
Electrochemical wastewater treatment processes
.
Advanced Physicochemical Treatment Technologies
,
57
106
.
https://doi.org/10.1007/978-1-59745-173-4_2
.
Chiang
L. C.
,
Chang
J. E.
&
Wen
T. C.
1995
Indirect oxidation effect in electrochemical oxidation treatment of landfill leachate
.
Water Research
29
(
2
),
671
678
.
https://doi.org/10.1016/0043-1354(94)00146-x
.
Clement
B.
,
Janssen
R. C.
&
Dù-Delepierre
A.
1997
Estimation of the hazard of landfills through toxicity testing of leachates
.
Chemosphere
35
,
2783
2796
.
https://doi.org/10.1016/S0045-6535(97)00332-9
.
Combes
R. D.
&
Haveland-Smith
R. B.
1982
A review of the genotoxicity of food, drug and cosmetic colour and other azo, triphenylmethane and xanthene dyes
.
Mutation Research/Reviews in Genetic Toxicology
98
(
2
),
101
243
.
https://doi.org/10.1016/0165-1110(82)90015-X
.
Comninellis
C.
1994
Electrocatalysis in the electrochemical conversion/combustion of organic pollutants for wastewater treatment
.
Electrochimica Acta
39
(
11–12
),
1857
1862
.
https://doi.org/10.1016/0013-4686(94)85175-1
.
Cong
Y.
,
Wu
Z.
&
Li
Y.
2008
Electrochemical inactivation of coliforms by in-situ generated hydroxyl radicals
.
Korean Journal of Chemical Engineering
25
(
4
),
727
731
.
https://doi.org/10.1007/s11814-008-0119-x
.
Croce
R.
,
Cinà
F.
,
Lombardo
A.
,
Crispeyn
G.
,
Cappelli
C. I.
,
Vian
M.
&
Baderna
D.
2017
Aquatic toxicity of several textile dye formulations: acute and chronic assays with Daphnia magna and Raphidocelis subcapitata
.
Ecotoxicology and Environmental Safety
144
,
79
87
.
https://doi:10.1016/j.ecoenv.2017.05.046
.
Daniel
C. H.
2007
Table of standard reduction potentials. Craig Bleyer, Library of Congress, p 5
.
DEPA (Danish Environmental Protection Agency)
2000
Survey of Azo-Colorants in Denmark. Toxicity and Fate of Azo Dyes. DEPA, Denmark, pp. 147–323
.
El-Gohary
F.
&
Tawfik
A.
2009
Decolorization and COD reduction of disperse and reactive dyes wastewater using chemical-coagulation followed by sequential batch reactor (SBR) process
.
Desalination
249
(
3
),
1159
1164
.
https://doi.org/10.1016/j.desal.2009.05.010
.
Farhataziz
&
Ross
A. B.
1977
Selective Specific Rates of Reactions of Transients in Water and Aqueous Solutions. Part III. Hydroxyl Radical and Perhydroxyl Radical and Their Radical Ions
.
National Standard Reference Data Series 59
.
Gaied
F.
,
Louhichi
B.
,
Bali
M.
&
Jeday
M.
2019
Tertiary treatment of wastewater by electro-coagulation, electro-Fenton and advanced electro-oxidation processes: comparative and economic study
.
Songklanakarin Journal of Science & Technology
41
(
5
),
1084
1092
.
Garcia-Segura
S.
,
Ocon
J. D.
&
Chong
M. N.
2018
Electrochemical oxidation remediation of real wastewater effluents — A review
.
Process Safety and Environmental Protection
113
,
48
67
.
doi:10.1016/j.psep.2017.09.014
.
Georgiou
D.
,
Aivazidis
A.
,
Hatiras
J.
&
Gimouhopoulos
K.
2003
Treatment of cotton textile wastewater using lime and ferrous sulfate
.
Water Research
37
(
9
),
2248
2250
.
https://doi.org/10.1016/s0043-1354(02)00481-5
.
Gogate
P. R.
&
Pandit
A. B.
2004
A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions
.
Advances in Environmental Research
8
(
3–4
),
501
551
.
https://doi.org/doi:10.1016/s1093-0191(03)00032-7
.
Gregory
J.
2005
Particles in Water Properties and Processes
.
IWA Publishing
,
London
.
Grimm
J.
,
Bessarabov
D.
&
Sanderson
R.
1998
Review of electro-assisted methods for water purification
.
Desalination
115
(
3
),
285
294
.
https://doi.org/10.1016/s0011-9164(98)00047-2
.
Guergour
S.
2014
Elimination des polluants organiques contenus dans les eaux usées par electro-fenton. Memory of Magister. Ferhat Abbas-Setif-1 University, Algeria, p. 29
.
Harris
D. C.
2007
Table of Standard Reduction Potentials. Craig Bleyer, Library of Congress, p. 5. Available from: https://sites.chem.colostate.edu/diverdi/C477/experiments/electrochemistry_cyclic_voltammetry/science%20references/table%20of%20standard%20reduction%20potentials%20-%20Harris.pdf (accessed 9 January 2019)
.
Hoigné
J.
&
Bader
H.
1983
Rate constants of reactions of ozone with organic and inorganic compounds in water-II
.
Water Research
17
(
2
),
185
194
.
https://doi.org/10.1016/0043-1354(83)90099-4
.
IARC
1982
IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Human, Some Industrial Chemicals and Dyestuffs
.
World Health Organization, International Agency for Research on Cancer
,
Lyon
,
France
, p.
29
.
James
K. J.
&
Stack
M. A.
1997
The impact of leachate collection on air quality in landfills
.
Chemosphere
34
,
1713
1721
.
https://doi.org/10.1016/S0045-6535(97)00028-3
.
Jardak
K.
2015
Développement d'un procédé d'oxydation électro-catalytique pour la dégradation de l’éthylène glycol. Memory of Magister, Québec University, pp. 46–48
.
Kahoul
S.
&
Belhachani
N.
2016
Utilisation d'un procédé d'oxydation avancée dans le traitement des eaux industrielles. Memory of Magister, KASDI Merbah Ouargla University, Algeria, pp. 9–30
.
Kim
T.
,
Park
C.
,
Shinb
E.
&
Kim
S.
2004
Decolorization of disperse and reactive dye solutions using ferric chloride
.
Desalination
161
,
49
58
.
https://doi.org/10.1016/S0011-9164(04)90039-2
.
Lakhdari
B.
2011
Effet de la coagulation floculation sur la qualité des eaux épurées de la STEP de Ain Al Houtz. Memory of Magister, Abou Bekr Belkaid Tlemcen University, Algeria, pp. 6–39
.
Lefebvre
E.
&
Legube
B.
1990
Coagulation par Fe (iii) de substances humiques extraites d'eaux de surface: effet du pH et de la concentration en substances humiques
.
Water Research
24
(
5
),
591
606
.
https://doi.org/10.1016/0043-1354(90)90192-9
.
Li
M.
,
Feng
C.
,
Zhang
Z.
&
Sugiura
N.
2009
Efficient electrochemical reduction of nitrate to nitrogen using Ti/iro2–Pt anode and different cathodes
.
Electrochimica Acta
54
(
20
),
4600
4606
.
https://doi.org/10.1016/j.electacta.2009.03.064
.
Lounnas
A.
2009
Amélioration des procèdes de clarification des eaux de la station Hamadi-Kroma de Skikda. Memory of Magister, Skikda Tlemcen University, Algeria, pp. 45–52
.
Mansour
H.
,
Boughzala
O.
,
Dridi
D.
,
Barillier
D.
,
Chekir-Ghedira
L.
&
Mosrati
R.
2011
Les colorants textiles sources de contamination de l'eau: CRIBLAGE de la toxicité et des méthodes de traitement
.
Revue des Sciences de l'eau
24
(
3
),
209
238
.
https://doi.org/10.7202/1006453ar
.
Martínez-Huitle
C. A.
&
Ferro
S.
2006
Electrochemical oxidation of organic pollutants for the wastewater treatment: direct and indirect processes
.
Chemical Society Reviews
35
(
12
),
1324
1340
.
https://doi.org/10.1039/b517632 h
.
Medvedev
Z. A.
,
Crowne
H. M.
&
Medvedeva
M. N.
1988
Age related variations of hepatocarcinogenic effect of azo dye (3′-MDAB) as linked to the level of hepatocyte polyploidization
.
Mechanisms of Ageing and Development
46
(
1–3
),
159
174
.
https://doi.org/10.1016/0047-6374(88)90123-6
.
Millet
M.
1992a
L'oxygène et les radicaux libres (1re partie)
.
Bios
23
,
67
70
.
Millet
M.
1992b
L'oxygène et les radicaux libres (2e partie)
.
Bios
23
,
45
50
.
Nabi
B. G. R.
,
Torabian
A.
,
Ehsani
H.
,
Razmkhah
N.
&
Abbasi
M.
2007
Evaluation of industrial dyeing wastewater treatment with coagulants
.
International Journal of Environmental Research
1
(
3
),
242
247
.
Percy
A. J.
,
Moore
N.
&
Chipman
J. K.
1989
Formation of nuclear anomalies in rat intestine by benzidine and its biliary metabolites
.
Toxicology
57
(
2
),
217
223
.
https://doi.org/10.1016/0300-483x(89)90167-4
.
Rahmani
A. R.
,
Godini
K.
,
Nematollahi
D.
,
Azarian
G.
&
Maleki
S.
2015
Degradation of azo dye C.I. Acid Red 18 using an ecofriendly and continuous electrochemical process
.
Korean Journal of Chemical Engineering
33
(
2
),
532
538
.
Rosie
J.
,
Shaharin
I.
&
Normala
H.
2012
Electro coagulation for removal of chemical oxygen demand in sanitary landfill leachate
.
International Journal of Environmental Sciences
3
(
2
),
921
930
.
https://doi.org/10.6088/ijes.2012030132020
.
Sefraoui
M.
2013
Etude comparative sur le prétraitement des eaux de mer par ultrafiltration et coagulation floculation. Memory of Magister, Abou Bekr Belkaid Tlemcen University, Algeria, pp. 40–49, 98–120
.
Seghairi
N.
,
Mimeche
L.
,
Bouzid
A.
&
Ayachi
Y.
2017
Traitement des eaux usées par coagulation – floculation en utilisant le sulfate d'aluminium comme coagulant
.
J. Wat. Env. Sci.
1
(
Special issue ICWR 2
),
230
234
. http://revues.imist.ma/?journal=jwes.
Sirés
I.
,
Brillas
E.
,
Oturan
M. A.
,
Rodrigo
M. A.
&
Panizza
M.
2014
Electrochemical advanced oxidation processes: today and tomorrow
.
Environmental Science and Pollution Research
21
(
14
),
8336
8367
.
https://doi.org/10.1007/s11356-014-2783-1
.
Szpyrkowicz
L.
,
Kaul
S. N.
&
Neti
R. N.
2005
Tannery wastewater treatment by electro-oxidation coupled with a biological process
.
Journal of Applied Electrochemistry
35
(
4
),
381
390
.
https://doi.org/10.1007/s10800-005-0796-7
.
Tipping
E.
&
Backes
C. A.
1988
Organic complexation of Al in acid waters: model testing by titration of a streamwater sample
.
Water Research
22
(
5
),
593
595
.
https://doi.org/10.1016/0043-1354(88)90060-7
.
Torres
N. H.
,
Souza
B. S.
,
Ferreira
L. F. R.
,
Lima
Á. S.
,
dos Santos
G. N.
&
Cavalcanti
E. B.
2019
Real textile effluents treatment using coagulation/flocculation followed by electrochemical oxidation process and ecotoxicological assessment
.
Chemosphere
.
https://doi:10.1016/j.chemosphere.2019.07.040
.
Tsuda
S.
,
Matsusaka
N.
,
Madarame
H.
,
Ueno
S.
,
Susa
N.
,
Ishida
K.
&
Sasaki
Y. F.
2000
The comet assay in eight mouse organs: results with 24 azo compounds
.
Mutation Research/Genetic Toxicology and Environmental Mutagenesis
465
(
1–2
),
11
26
.
https://doi.org/:10.1016/s1383-5718(99)00199-0
.
Vasudevan
S.
&
Oturan
M. A.
2013
Electrochemistry: as cause and cure in water pollution-an overview
.
Environmental Chemistry Letters
12
(
1
),
97
108
.
https://doi.org/10.1007/s10311-013-0434-2
.
Verma
P.
&
Samanta
S. K.
2018
Microwave-enhanced advanced oxidation processes for the degradation of dyes in water
.
Environmental Chemistry Letters
16
(
3
),
969
1007
.
https://doi.org/10.1007/s10311-018-0739-2
.
Verma
A. K.
,
Dash
R. R.
&
Bhunia
P.
2012
A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters
.
Journal of Environmental Management
93
(
1
),
154
168
.
https://doi.org/10.1016/j.jenvman.2011.09.012
.
Zaviska
F.
,
Drogui
P.
,
Mercier
G.
&
Blais
J.
2009
Procédés d'oxydation avancée dans le traitement des eaux et des effluents industriels: application à la dégradation des polluants réfractaires
.
Revue des Sciences de l'eau
22
(
4
),
535
564
.
https://doi.org/10.7202/038330ar
.
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