Optimization of continuous electrocoagulation-adsorption combined process for the treatment of a textile effluent

Kamel Hendaoui,Malika Trabelsi-Ayadi,Fadhila Ayari

Laboratory of Applications of Chemistry to Natural Resources and Substances and the Environment (LACReSNE),University of Carthage,Faculty of Sciences of Bizerte,Zarzouna 7021,Tunisia

Keywords:Combined process Textile effluent Electrocoagulation Adsorption Decontamination efficiencies Response surface methodology

ABSTRACT The aims of this study is to design and optimize the functioning of a full continuous combined process based on electrocoagulaion-adsorption on crude Tunisian clay to treat a real textile effluent.The clay characterization shows that the used clay is a rich-smectite clay.The response surface methodology(RSM)technique based on Box-Behnken design(BBD)was used to optimize the process.At optimum conditions which are initial pH solution of 8.24,effluent flow rate of 0.5 L?min-1,voltage of 70 V,and added suspension of clay flow rate of 100 ml?min-1 the achieved color,chemical oxygen demand (COD) and total suspended solid (TSS) removal efficiencies were respectively 96.87%,89.77% and 84.46% with 0.75USD?m-3 as total cost.The additional laboratory experiments at optimum conditions agree with the predicted results,which confirm the accuracy and the capability of RSM to predict results in the defined space.Finally the designed process could be a good eco-friendly alternative to treat and reuse wastewater in industrial process with reasonable cost.

1.Introduction

In Tunisia,water resources are limited because of the semi-arid to arid climate in the most of the territory.The water resources currently available are estimated at 430 m3per inhabitant.The preservation of actual resources and the use of unconventional resources have become a necessity in order to compensate the deficit between the resource and the needs.However,the textile and clothing sector is in full expansion in Tunisia and count more than 2000 enterprises and 160 thousand employees.It is considered among the most water consuming activity.Petrini?et al.[1] have indicated that one kg of a finished textile product consumes about 200 L of water.Consequently,high quantities of effluent,which generate a potential nuisance for the environment and human life(pollution of the rivers,contamination of groundwater,epidemiological risks,bad smells,etc.).According to Balanoskyet al.[2],these effluents are loaded with toxic products,namely dyes,detergents,fats,suspended solids,salts,sulphate and fibers.Moreover,they are characterized by strong colors,high levels of pH,temperature and high organic components load[3,4].These pollutants are carcinogenic,mutagenic and resistant to biodegradation [5].According to de Moraeset al.[6] this resistance is related to dyes,surfactants and other adjuvant used in large quantities by these industries.Face to this challenge,the treatment of this type of pollutions and its reduction at the sources become a necessity.In fact,many studies have been conducted to decontaminate these effluents by identifying the appropriate process.Coagulationflocculation techniques are widely used to remove colors.However,they have a low efficiency and they generate a huge amount of sludge [7–9].

Adsorption methods become more and more attractive,due to their high efficiency,eco-friendly characteristics as well as their regeneration ability [10,11].Nevertheless,the adsorbents application is restricted due to numerous problems such as high cost of regeneration especially in case of activated carbon [12],sludge regeneration and displacement of pollution[13].For these reasons,other researchers used doped or activated biochar to resolve soil contamination by the generated sludge [14,15].The biological treatment method removes generally the dissolved compound.The process efficiency depends on the ratio of biodegradability components load,the microorganism load as well as the process conditions (temperature,oxygen concentration,etc.),since the most of microbial microorganism presents a high sensitivity toward organic toxicity and temperature variation [16–19].For the filtration process,the challenges that face researchers are the membrane fouling,the high process cost and the frequency of maintenance [20,21].Unfortunately,these various available techniques of treatment have many drawbacks;consequently,cannot be effectively used individually.Therefore,the best solution for textile mill effluent treatment involves the combination of several efficient methods.Thus,to benefit from the cumulated advantages of different process,the aim of this work is to perform the decontamination of a real textile effluent loaded with blue indigo dye using a combined process.On one hand by conceiving a full continuous combined process based on electrocoagulation and adsorption on a Tunisian raw clay,on the other hand by optimizing the most influencing parameters using the response surface methodology (RSM).This process sequence was chosen in the virtue of diverse benefits namely eco-friendly,energy efficiency,safety,easy automation and cost.In fact,recently the researchers concentrate their efforts on the electrocoagulation(EC)process,which provides a simple,consistent and cost-effective method for the treatment of textile effluent and dye removal without additional chemical products.Subsequently the pollutants and sludge deposited on the electrode are the only secondary pollution[16,22–27].The EC method reduces also the quantity of sludge that should be disposed [28].The pollutant removals by electrocoagulation such as heavy metal[29],hydrocarbons [30,31],leachate [32],and diverse other ions[33,34] were also reported.

The decontamination of real textile effluent loaded with blue indigo dye using EC process has been previously studied by Hendaouiet al.[35] who have confirmed the efficiency of the process for color removal although the persistence of organic pollutants,since the maximum COD removal was of 76.1%at optimum conditions.However,Gil Pavaset al.[36] and Seculaet al.[37] studied the combined electrocoagulation-activated carbon adsorption process and they prove its efficiency to decontaminate a real textile effluent.Moreover,in 2017 Gil Pavaset al.[38] showed the applicability of a combined EC/Electo-oxidation process for the treatment of a real textile wastewater with a competitive total operating cost of 1.47 USD?m-3.

The adsorption on clay and clay mineral was widely reported as efficient technique for the removal of dyes,color,and heavy metal from industrial wastewater [39–43].However,not very efficient for COD removal especially for high loaded effluent with organic compound and real effluent [44].In this work,the Tunisian raw clay was used as a second step in a second reactor to adsorb the excess released soluble iron and to reduce the remained COD.

2.Materials and Methods

2.1.Effluent samples and chemicals

The textile effluent samples were obtained from the local Tunisian textile factory (SITEX) which produces approximately 800 m3of wastewater per day.The effluent is loaded with indigo dyes,vat dyes,salt,wetting agent,hydrosulfite,dispersing agent and other auxiliary agents.The wastewater samples were collected from the equalization tank immediately after dyeing,finishing and rinsing process.The samples were stored at 4°C in opaque containersand used without any previous treatment.Table 1 shows the composition of the used wastewater in the subsequent study before treatment and the discharge limit according to the Tunisian standard.

Table 1 Raw effluent samples characteristics and discharge limit

The chemical products are of analytical grade and used without supplementary purification for the characterization of the clay(adsorbent) and for the adjustment of the pH solution.

2.2.Clay sample

The raw clay was collected from Rommana deposit (Gabes) in south Tunisia.The raw clay was sieved in particles sizes lower than 60 μm,dried during 36 hours at 100°C to remove moisture,and then used without further treatment.The fraction with the size ≤2 μm was used only to identify the clay mineralogy.

2.3.Analytical measurement

The measurements of COD (chemical oxygen demand) and the color were evaluated in accordance with the procedure of a standard method using HACH LANGE DR3900 UV–Vis spectrophotometer.The pH was measured using a HANNA INSTRMENT pH meter.The voltage and current were measured with multi-parameter digital METRIX PX110.Treated samples were centrifuged during 30 min at 4000 r?min-1and the obtained supernatant liquid was filtered prior analyze.

The MES is calculated according to Eq.(1)

whereWfandWiare respectively the mass (mg) of filter at 105°C after filtration and before filtration.Vsis the volume of sample(ml) (BS EN 872:2005,BS 6068–2.54 :2005).

The removal efficiencies(%)of:ColorR1,CODR2and TSSR3are calculated according to the following Eq.(2)

CiandCfare respectively the initial and final color(Pt-Co),COD(mg?L-1) or MES (mg?L-1) of the untreated and treated samples.

2.4.Material design and procedure

As shown in Fig.1,the full continuous electrocoagulationadsorption pilot station is made from high-density polyethylene(HDPE).It is made essentially from two connected reactors.The first one is dedicated to the electrocoagulation and is composed of a rectangular column of capacity 1.4 liters and contains a set of 10 parallel iron electrodes spaced 4 mm from each other and connected in bipolar mode,two power blades and electrode guides.The electrodes are fully emerged in the wastewater,thus allowing an effective volume of 1 liter and a total effective area of 761.6 cm2.The EC cell was fed through the two power blades by an alternating current generated by a power supply with an input of 220 V and variable output of 0–220 V and a maximum current of 16 A.The raw effluent was fed from the bottom of the EC reactor continuously using a frequency variable pump to control the flow rate.The second reactor of 2.5 liter capacity is dedicated to the adsorption on clay.It is a cubic chamber equipped with a mechanical stirrer powered by a 12 V DC generator.

Once pre-treated with EC,the effluent migrates to the adsorption chamber through a hole connecting both reactors from the top.The pretreated effluent is systematically mixed with the clay in the second reactorviathe mechanical stirrer.The clay was put in advance in suspension solution of 50 g?L-1in acrylic container and the suspension was kept homogeneous using a mechanical mixer.The added clay (clay suspension) to the adsorption reactor was adjustedviaa 12 V peristaltic pump.Finally,the treated effluent is transferred to a cylindrical tank for sedimentation.

Fig.1.Experimental setup:(a)Real schematic of pilot,(b)3D scheme of pilot.1:tank with untreated effluent,2:variable frequency pump,3:electrocoagulation reactor,4:Adsorption reactor,5:mechanical stirrer,6:tank for sedimentation,7:acrylic container of the suspension of clay,8:mechanical mixer of the suspension of clay,9:12 Volt peristaltic pump,10:control panel of current supplier,11:10 parallel iron electrodes.

After each run,the oxide films were detached and the electrodes were polished with a wire brush and cleaned with 1 mol?L-1H2SO4and distilled water.

The heavy pollutants and sludge are removed after sedimentation in the bottom of EC reactor after experience.The other floated pollutants are removed from the second reactor.

2.5.Experimental design and process optimization

In the present study,the Box-Behnken design (BBD) for response surface methodology (RSM) with 3-level 4-factor was applied to inspect and optimize the most affecting parameters of the full continuous electrocoagulation-adsorption process.This design is rotatable or nearly rotatable second-order design class[45].It is suitable for (i) the estimation of the optimum values of factors,(ii) fitting a second order polynomial and quadratic surfaces used to investigate the effect of input factors (parameters)as well as their interaction,(iii)use of blocks and(iv)identification of lack-of-fit of the model[46].This design requires the minimum number of experiments (N) which is defined by Eq.(3)

wherekis number of parameters andn0is the number of central points.

Table 2 shows the BBD design with four input parameters namely initial solution pH,voltage (volt/V),effluent flow rate (Eff FR/L?min-1)and clay suspension flow rate(Clay FR/ml?min-1)varied at three levels (-1,0,1).The ranges of each parameter were chosen based on the preliminary experiments,which show a non linear evolution of the responses and their stagnation after the upper and low values.

Table 2 Input factors and level

Taking in account all the linear terms,square terms and linear interaction items,the second order polynomials(Y)related to color removal,COD removal and TSS removal efficiencies can be described by Eq.(4)

whereYis the response,β0is a constant,βithe linear effect,βijthe linear by linear interaction,βiiis the quadratic interaction andXiandXjare the coded factors (parameters).

The results were evaluated by the coefficient of determination(R2),the statistical analysis of variance(ANOVA),the quadratic surfaces (response plots) and finally by the Derringer’s desirability function [47] determined with the software Minitab 14v.

3.Results and Discussion

3.1.Clay characterization

The characterization of the crude clay using the X-ray Diffraction (XRD),Fourier transforms infrared spectroscopy (FTIR),X-ray fluorescence (XRF) and titrimetric methods shows that the used adsorbent is smectite-rich clay having a large specific surface area(SSa) and a high cation exchange capacity (CEC) that enhance its adsorption capacity.Table 3 summarizes the mineralogical composition of the clay and Table 4 shows its physicochemical characteristics.

3.2.Process analysis with BBD

In Table 5 are gathered the BBD design matrix as well as the observed (Obs) and the predicted (Pre) values for color removal(R1/%),COD removal (R2/%) and TSS removal (R3/%) efficiencies.

According to Table 5 the obtained experimental values are in good agreement with the BBD predicted values for all responses.The higher values for color,COD and TSS removal efficiency are obtained in run 8 and 23 at initial solution pH of 8 and the highest voltage of 70 V.However,the low values were obtained in run 22 at the lowest voltage value and highest effluent flow rate.The high coefficient of correlation and the good harmony with their adjusted values respectively of 98.9%,97.7% for color removal,98.7%,97.2% for COD removal and 98.8%,97.4% for TSS removal prove the high accuracy of the developed models (Full quadratic polynomials)by the RSM in term of uncoded units.The significance of the different operating parameters and their interactions wereinvestigated by studying theP-value at 95%confidence level,which means,ifP-value<0.05,the coefficient of regression is significant.The estimated regression coefficients for color,COD and TSS removal efficiencies are summarized in Table 6.

Table 3 Mineralogical analysis of the clay

Table 4 Physicochemical characteristics of the clay

Form Eq.(4)and by taking in account only significant coefficient from Table 6,the developed three full quadratic regression models are defined by Eqs.(5)-(7) as the following:

The plot of predicted valuesversusthe obtained results in Fig.2(a)-(c) form a straight line,and errors are normally distributed since residuals are randomly disseminated (plot of residuals not shown) proving the statistical significance of the three developed models by RSM and their capability to describe the decontamination phenomena and to predict the responses.

In order to deepen the investigation,the analysis of variance(ANOVA) shown in Table 7 was used to verify the reliability and reproducibility of the fitted models.Thus,Pvalue=0 for the all regressions and the very low sum of square of residual error in comparison to the total sum square for the three responses,prove the efficiency and the reliability of the models at a 95%confidence level.

Table 5 BBD design matrix along with observed and predicted removal efficiencies

Table 6 Estimated regression coefficients for color,COD and TSS removal efficiencies and T and P values

Table 7 Analysis of variance (ANOVA) for color,COD and TSS removal efficiencies

3.3.Effects of operating parameters

The main effect plots (Fig.3) and the 3D surfaces plots (Fig.4)were used to evaluate the effects of each parameter and to optimize the process.

3.3.1.Effect of initial pH of effluent

It has been recognized that the pH of effluent is among the factors influencing the performance of electrocoagulation [48,49].At neutral pH range,many coagulant species such as Fe2（H2O）8and Fe2（H2O）6are generated.They enhance considerably the adsorption and coagulation phenomenon.Sengil&?zacar[50]reported also in Fig.5,that different species are produced all through EC process.The main efficient species on coagulation are Fe(OH)3and are generated at neutralto basic pH range (pH from 6 to 9.8) allowing a high efficiency of pollutants removal at slightly basic solution range.

Fig.2.Predicted versus obtained results for:(a) color removal (b) COD removal and (c) TSS removal efficiencies.

Eqs.(8)-(14) show the most important reactions during electrocoagulation using iron electrodesversuspH levels.

Fig.3.Main effect plots for (a) color removal (R1),(b) CoD removal (R2) and (c) TSS removal (R3).

Fig.4.3D plot at middle levels for (a) color removal (R1),(b) COD removal (R2),(c) TSS removal (R3).

Fig.5.Predominance-zone diagrams for Fe(III) chemical species versus pH in aqueous solution [50].

In addition to the reactions elicited,some other reactions expressed by Eqs.(15)–(17) occur at pH lower than 11,because of the presence of the salts (NaCl) used in dyeing bath [24,51].The produced hypochloriteviaionization of hypochlorous acid enhances considerably the decontamination of the textile effluentviaoxidation process.

Moreover,as reported by O.Tünayet al.[52]the above chlorine(secondary species) are responsible for organic pollution removal and can be also a good oxidants for sulphite and thiosulphate which are transformed to sulphate.

At the same time,the NaCl improves the iron dissolution by reducing the electrodes passivation and by enhancing the solution conductivity.

Concerning the adsorption process,indigo dye is assimilated to anionic dye in soluble form.Its adsorption on clay is more efficient at acidic conditions.Akar and Uysa [53]have found that in case of using montmorillonite clay,the acidic conditions enhance the adsorption yield of anionic dyes.In addition,Mittalet al.[54]have confirmed that the best adsorption efficiency of indigo caramine was at acidic pH level(3–4).This phenomenon could be explained by the electrostatic attraction between the positive charge on the edges of the clay and the negative charge of dye in soluble form.Indeed,aluminols(Al—OH)and silanols(Si—OH)groups at tetrahedral and octahedral sheets capture or release proton depending on pH and according to Eqs.(18)–(21).

In our study,the pHpzcof the used smectite-rich clay is equal to 8.4,which means that the lower is the pH of solution,the more the clay surface is positively charged.Thus,the adsorption is enhanced.However,the combined synergy between electrocoagulation and adsorption has almost neutralized the effect of the pH (run 2 and run 20).Confirmed by the plot in Fig.3 (a–c),the pH level does not affect seriously the response of the combined process since it forms almost a horizontal line parallel to theXaxis.Thus,under acidic conditions,adsorption is favored and electrocoagulation is penalized,but under slightly basic conditions,it is electrocoagulation that is favored.From 3D plots in Fig.4(a–c),it is shown that effluent decontamination increases when the pH increases from 5 to 8 and the best decontamination efficiency was achieved at pH in range of 8.

3.3.2.Effect of the inlet effluent flow rate

As known,the inlet effluent flow rate is inversely proportional to the both EC residence time and adsorption contact time.Which means,the lower effluent flow rate implies a longer residence and contact time,which allows to the producedin-situcoagulant molecules,adsorbent,dye and pollutant compounds to mix properly,thus improving the continuous process performances.Moreover,Eq.(22)confirms that the lower effluent flow rate involved a great quantity of released iron which enhances the quantity of the generated flocks Fe(OH)2,Fe(OH)3and ferric polymers species,which improves the EC decontamination efficiencies.About adsorption,at shorter contact time (high flow rate) the pores of clay are not occupied with impurity and capture quickly the suspended and the dissolved matter,which explains the high impact of flow rate on the process when it decreases from 1.5 L?min-1to 1 L?min-1.Fig.3(a)–(c)and Fig.4(a)–(c)show the more the effluent flow rate is higher the more the pollutants removal efficiencies are lower.These results agree with previous results reported by Taheriet al.[55]and Seculaet al.[56]who indicate that the best synthetic solution decolorization was achieved at the highest retention time when using EC process.Therefore,when the effluent flow rate is under 1 L?min-1,the pollutant uptakes becomes lower.This is mainly due to the saturation and the total coverage of the faces and edges of the clay.

3.3.3.Effect of the current density

The current density is among the most important parameters that affects the EC process.In fact,the quantities of polymers and iron oxide flocks generated form iron electrodes depend,according to Eq.(22) on current density,which is in turn proportional to voltage.

It should be noted that during all experiments,the current density defined as the ratio of current at the total electrodes area(j=i/Aelectrodes,A?m-2)was calculated after measuring the current in the EC cell.It was changed between 1.3 mA?cm-2and 21 mA?cm-2.

From Fig.3 (a)–(c),it is shown that the color,the COD and the TSS removal efficiencies were improved quickly when the current density increases.In the run 7 and run 8,at fixed parameters values(pH=8,effluent flow rate=1 L?min-1and added suspension of clay flow rate=100 ml?min-1),the color removal,COD removal and TSS removal efficiencies increase respectively from 78.2% to 92.01%,73.03% to 86.79%and from 71.19%to 82.9%when the current density increases from 3.28 A?m-2to 10.5 A?m-2(voltage increases from 10 to 70 V).On the other hand,during experience it was observed that the high current density fastens the speed of decontamination.This phenomenon is explained by the small size of H2bubble and the large amount of iron hydroxide flocks generated at a higher current density.However,electrical cost and electrode consumption are closely related to voltage and increase with the increase of voltage.These results agree with the previous results reported by Seculaet al.[57],Bazrafshanet al.[58],Tünayet al.[52] who have confirmed that the best removal efficiencies were obtained at the higher current density.

It was observed during experiences that the current decreases gradually with treatment time,especially at high voltage level and low effluent flow rate,which could be explained by electrode passivation and the decrease of the solution conductivity.

3.3.4.Effect of the added suspension of clay flow rate (adsorbent dosage)

The clay dose(suspension of clay flow rate)injected in the second reactor dedicated for adsorption was adjustedviaperistaltic pump at three levels (20,60 and 100 ml?min-1which equivalent to 1,3 and 5 g?L-1of added clay).As it could be seen in Fig.3(a)–(c),all pollutant removal efficiency depends on the amount of added clay (suspension of clay flow rate) to the solution.An increase of the flow rate of the added suspension of clay increases the decontamination efficiency.However,in Fig.4 (a–c) the process yield was steeply enhanced when the flow rate of the suspension of clay increases from 20 to 60 ml?min-1(from 1 to 3 g?L-1).This result could be explained by the increase of the total surface area of adsorbent(crude clay)in solution and the remained unsaturated sorption sites [59,60].On the other hand,this proves the strong affinity between the used smectite-rich clay and pollutants and dyes in textile effluent.In the 3D plot Fig.4(a–c),although the observed increase in the pollutant removal efficiency with increasing the added clay,there is an optimum dosage around 60 ml?min-1above which there is no significant increase in the decontamination efficiency especially at high voltage and/or slow inlet effluent flow rate.

To estimate the adsorption capacity of the clay,we compared two effluent samples under the optimum conditions.The first was collected from the EC reactor before adsorption process and the second was derived from the full process.The results show that the adsorption enhances the color removal,the COD removal and the TSS removal efficiencies respectively from 87.3% to 96.58%,from 81.4% to 89.62% and from 73.75% to 84.5%.

3.4.Process optimization

Fig.6.Process optimization for Color removal (R1),COD removal (R2) and TSS removal (R3).

The most important aim of the current work is to optimize the process by the determination of the optimum values of the operating parameters,which allows the height decontamination efficiencies.Thus,the software optimization module of minitab 14,searches the best combination of factors (parameters) levels to optimize the three responses developed by the RSM and presented in Eqs.(8)–(10)at the same time.On the contrary,the 3D plots and contour plots allow optimizing only two parameters by two simultaneously.The investigated factors are chosen without initial starting values while the response goals of color,COD and TSS removal efficiencies were defined at maximum values (100%) in order to achieve the highest performances of the conceived pilot.Fig.6 shows that at optimum conditions which are:pH 8.24,Eff FR of 0.5 L?min-1,volt of 70 V and Clay FR of 100 ml?min-1the predicted color,COD and TSS removal efficiencies were respectively 96.5%,89.57%and 85.14%.Finally,to check the performance,the accuracy and the sufficiency of the developed model three supplementary laboratory experiments were conducted at the obtained optimum conditions.Table 8,which gathers the predicted and complementary experiment results,shows that the means errors between experimental and predicted results are respectively:0.37%,0.2%and -0.68% for color,COD and TSS removal efficiencies.The good agreement between the results confirms the accuracy and the capability of the RSM design to predict the full continuous combined process results at the defined experimental space.

Table 8 Experimental and predicted results at optimum conditions for R1, R2 and R3

Finally,the test of treated effluent on three samples of yarns shows that the remained toxicity after treatment which is:Color of 91Pt-Co,COD of 224 mg?L-1,TSS of 65 mg?L-1and less than 1 g?L-1of oil and grease does not damage the yarns when treated effluent is reused for preparation.

3.5.Operating cost

The operating costs are very important to judge the efficacy of a treatment process.In actual process,operating costs includes in particular,the costs of electrical energy and electrodes material,the cost of the raw clay,maintenance and staff costs.However,Doniniet al.[61] and Bayramogluet al.[22] reported that energy and electrodes costs were the major cost items in the EC process.In the current work,the consumed electrodes [ElC/(kg Fe)?m-3]are expressed by Eq.(22) as reported by [53,62].

The energy consumption(EnC/kW?h?m-3)expressed by Eq.(23)includes only the EC cell energy consumption.

In the equations above:U,I,t,V,A,n,F,α,β,Cc,CsandCmare respectively:Cell voltage(V),current intensity(A),treatment time(hour),Volume of treated sample (m3),atomic mass of iron(55.845 g?mol-1),number of electrons implicated in oxidation/reduction (n=2 for iron),Faraday’s constant (96485 C?mol-1),localprice of unit kW?h (0.087 USD),price of iron electrodes (0.78 USD?kg-1),cost of clay (0.026 USD?kg-1),staff cost (0.028 USD?m-3),maintenance cost (0.019 USD?m-3).

Thus,the total cost calculated according to Eq.(24) was 0.75 USD?m-3.

Espinoza-Qui?oneset al.[63],found that operational cost for EC alone,was 1.7 USD?m-3of treated tannery effluent.Although the reported cost in the studies of Merzouket al.[64],Hakizimanaet al.[65] were higher than 0.75 USD (our finding),they consider that electrocoagulation is among the cheapest technique of wastewater treatment.

4.Conclusions

In this study,performance of full continuous electrocoagulation-adsorption on crude clay pilot for treating a real textile mill effluent was investigated.The process optimization was executed using response surface methodology (RSM) and the effect of four operating parameters namely initial pH solution,effluent flow rate,voltage and added suspension clay flow rate on effluent decontamination have been surveyed.According to the results analysis,the color,COD and TSS removal efficiencies increased by voltage and suspension of clay flow rate increases and effluent flow rate decreases.However,pH solution doesn’t have a significant effect on the process and the highest performance was achieved at the neutral pH range.At optimum conditions,which are pH of 8.24,Eff flow rate of 0.5 L?min-1,voltage of 70 V and Clay FR of 100 ml?min-1the achieved color,COD and TSS removal efficiencies were respectively 96.87%,89.77% and 84.46%.The additional experiments are in good agreement with predicted results and it turned out the accuracy and the efficiency of the developed model.The novel combined process could be an effective solution to treat a real industrial wastewater with cheaper cost (0.75 USD?m-3) compared to the conventional methods.Finally,the residual pollutant does not pose a problem for reusing the treated effluent in the preparation process.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

I would like to express my deepest appreciation to all those who provided me the possibility to achieve this work.A special thanks to the SITEX managers and employees for providing equipment,effluent and their proficiency and trust.I sincerely thank the technical team of the national office of mines for providing equipment and for their help to characterize the local clay.My warm thanks also to the editor and reviewers for their time and valuable feedback.