Electrocoagulation–electroflotation as a surface water treatment for industrial uses

Separation and Purification Technology 74 (2010) 342–347

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Electrocoagulation–electroflotation as a surface water treatment for industrial uses Catherine Ricordel a,∗ , André Darchen b , Dimiter Hadjiev c a b c

Ecole des Métiers de l’Environnement, Campus de Ker Lann, 35170 Bruz, France UMR CNRS 6226 Sciences Chimiques de Rennes, ENSCR, CS 50837, avenue du Général Leclerc, 35708 Rennes Cedex 7, France Laboratoire de Biotechnologie et Chimie Marine, Université de Bretagne Sud, Centre de Recherche, rue Saint Maudé, 56132 Lorient, France

a r t i c l e

i n f o

Article history: Received 2 March 2010 Received in revised form 29 June 2010 Accepted 30 June 2010 Keywords: Bacteria Disinfection Aluminum Nanoparticles Adenosine 5 -triphosphate

a b s t r a c t Water is a natural product that is needed in many industrial uses, but some processes like washing or cooling do not require drinking water. In this work we investigated the efficiency of an electrolytic treatment of surface waters in order to increase their quality. The waters were taken from a river and in a pond and they were treated by electrocoagulation–electroflotation with an aluminum soluble anode. Vital nutriments for the bacteria development were consumed during the electrolysis. This treatment led to great decreases of molecular oxygen, phosphate and nitrate anions and dissolved organic compounds. Each of these decreases may explain the disinfection effect that was observed for the total flora. Moreover, the X-ray diffraction of the electro-generated solid showed the presence of nanocrystallites that could be involved in a bactericidal effect. After the electrocoagulation–electroflotation treatment, the investigated waters exhibited an increased quality for a cooling use. © 2010 Elsevier B.V. All rights reserved.

1. Introduction The deterioration of the quality and the decrease of the quantity of water lead to a greater interest in treating or recycling waters with physical means such as membrane separation or electrolytic process [1–5]. Electrocoagulation–electroflotation (ECEF) appears as a promising and efficient electrochemical technology [6–11]. ECEF is an electrolytic treatment whereby a sacrificial iron or aluminum anode dissolves and produces coagulant ions Al3+ or Fe2+ , while the cathode reaction affords hydrogen that is involved in a flotation process. Electrocoagulation and ECEF offer some advantages over traditional chemical coagulation: less coagulant ion is required and consequently less sludge is formed. ECEF equipments are compact and suitable installations are available. Furthermore, the coagulant injection into the solutions is easily managed by controlling the electrolytic current. A number of papers are devoted to the ECEF treatment of wastewater [6,12–19]. It has been noted that iron anode leads to a green color into treated water which then turns yellow and turbid [6,20–22]. This effect is due to the formation of Fe2+ ions that are oxidized to Fe3+ in the presence of oxygen. Fe(OH)3 formation and its precipitation affords yellow water and increases its turbidity. This drawback is a good reason for choosing aluminum electrodes

∗ Corresponding author. Tel.: +33 299058800; fax: +33 299058809. E-mail address: [email protected] (C. Ricordel). 1383-5866/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2010.06.024

in ECEF processes. Indeed, electrolysis of wastewaters with aluminum soluble anode has been well documented by numerous authors [11,13,23–25]. Electrolytic dissolution of the aluminum anode leads to various mononuclear and polynuclear species that are involved in coagulation process in solution. This coagulation affords gelatinous charged hydroxo-cationic complexes which are able to remove pollutants by adsorption and charge neutralization. ECEF treatment is an alternative to conventional chemical coagulation using Fe or Al salts. In ECEF, the coagulant is generated by electrolytic oxidation of an anode. Removal mechanisms occurring in the ECEF process involve coagulation, adsorption, precipitation and flotation [26–29]. The advantages of ECEF on conventional chemical coagulation include a low consumption of alkaline reagents thanks to a minor change of pH. The direct handling of corrosive chemicals is almost eliminated and the process can be easily adapted for use in portable water treatment units [7,8,30]. Electrochemical disinfection has shown a great interest, as one of the alternatives to conventional chlorination due to its effective environmental compatibility. A lot of studies concern electrolysis which generates a variety of oxidants in the presence of molecular oxygen, including hydrogen peroxide and ozone, as well as free chlorine and chlorine dioxide when chloride ions are present in the solution [31–33]. Disinfection effect of electrocoagulation has been recently published, but the question remains open on how does it work? We were interested by using ECEF in the objective of treating surface waters taken in a river and a pond in order to obtain

C. Ricordel et al. / Separation and Purification Technology 74 (2010) 342–347 Table 1 Physicochemical characteristics of river and pond water. Parameters −1

CAT (mequiv. L ) Chloride (mg Cl− L−1 ) Total hardness (Ca, Mg) (◦ F) Hardness (Ca) (◦ F) Nitrate (mg L−1 ) Phosphate (mg L−1 ) Total suspended solids, TSS (mg L−1 ) Permanganate index (mg O2 L−1 )

River water

Pond water

1.79 7.82 11.33 7.13 13.50 0.10 0.05*E−02 6.35

0.93 10.37 – 6.00 7.00 0.55 1.1*E−03 7.63

343

Light Units (RLU), then transformed by calibration in pg mL−1 of ATP and finally converted into equivalent bacterium. Eq. (1) was used to calculate the Quench–Gone cATP, where RLUUCI was the calibration result. QGA allows the measurement of the cellular concentration cATP and the determination of the equivalent microorganism concentration. For Total Control parameters, we realized two tests: total ATP (tATP) and extra cellular (dATP). Relationships ((2) and (3)) were used to calculate Total Control parameters. In Eq. (1) cATP is the intracellular ATP concentration of living organisms and it is given by Eq. (4): cATP (pg mL−1 ) =

RLUcATP 10, 000 × RLUUCI sample volume (mL)

(1)

tATP (pg mL−1 ) =

RLUtATP × 20, 000 RLUUCI

(2)

dATP (pg mL−1 ) =

RLUdATP × 10, 000 RLUUCI

(3)

waters able to be used in water cooling towers. For this goal, it was necessary to study the performances of the electrocoagulation towards the removal of the essential nutriments for bacterial flora and the flora able to be present in these waters. We thus made chemical and bacteriological studies of two surface waters treated by electrocoagulation by using aluminum electrodes. Further, the energy consumption has been determined.

cATP (pg mL−1 ) = tATP − dATP

2. Experimental

2.4. Chemical analysis

2.1. Water substrates

All chemical analyses were carried out by following standard methods: Alcalimetric Title and Complete Alcalimetric Title (AT and CAT) NF EN ISO 9963-1 (T 90-036); total hardness (Mg2+ + Ca2+ ) (NF T 90-003); hardness (Ca2+ ) (NF T 90-016); chloride (NF T 90014); permanganate index (KMnO4 ) NF EN ISO8467 (T 90-050); suspended matters (NF T 90-105); phosphate NF EN ISO 6878 (T 90-023). Nitrate concentration was measured by the Reflectoquant method (Merck). The detection range was between 5 and 225 mg L−1 .

All the experiments were performed with tap water or water samples taken in a river and a pond. These samples were stored at 4 ◦ C and brought to room temperature before experimentation. Table 1 gathers the main physicochemical data of these surface waters. 2.2. Equipment and electrolysis The ECEF reactor was a 2 L electrolytic cell with two parallel aluminum plates, each having a surface area of 38.4 cm2 . The electrodes were installed vertically in the middle of the reactor with an electrode gap of 2 cm. Before electrolysis, the electrodes were immersed in 2 M NaOH during 5 min and then rinsed with water. Finally, they were dried with absorbent paper and weighed. The electrodes were connected to a DC power supply (Micronix MX3001) providing a controlled voltage or current up to 300 V or 1 A, respectively. All the runs were performed at room temperature, under a magnetically agitation. Current intensity was chosen in order to avoid any heating of the solution, a phenomenon which would influence the disinfection action of electrolysis. The applied tension and the water temperature were measured during the electrolysis. The conductivity and the pH of the waters were measured with a WTW 315i apparatus. After each run, the aluminum electrodes were washed with water, dried and weighed. Water samples were taken and used for analysis after sedimentation. Neither centrifuging nor filtration was performed. Parallel blank analyses were carried out on untreated waters. 2.3. Bacteria analysis Total bacteria and algae were counted according to the standard method NF EN ISO 6222(T 90401) [34]. The count of the revival colonies was obtained at 37 ◦ C on Plate Count Agar (PCA). Two characteristics were determined: (i) T0 , the initial bacterial concentration in unit forming colonies (UFC mL−1 ) and (ii) Tf , the final bacterial concentration (UFC mL−1 ). For the effluent analysis, the Quench—Gone cATP (QGA) technology was used. The decanted solid was analyzed for Total Control for Microbial growth control (TCM). TCM and QGA are technologies from LuminUltra working on the measurement of adenosine 5 -triphosphate (ATP). ATP is a direct and interference-free indicator of the total biomass. The results are first expressed in Relative

(4)

2.5. Electrochemical analysis Specific electrochemical analyses were done during electrolysis performed in a 0.5 L three-neck round-bottom flask equipped with aluminum electrodes, a platinum electrode and a saturated calomel electrode (SCE) as a sensor of the oxidation reduction potential (ORP) and with a Clark electrode for the oxygen concentration measurement. The electrolysis was stopped during the electrochemical measurements. 2.6. X-ray diffraction The solid obtained after electrolysis carried out in 0.01 M NaCl with a soluble aluminum anode was collected by filtration. It was washed with water, dried at 105 ◦ C and then characterized by X-ray powder diffraction (Bragg-Brentano geometry, Rigaku-Geigerflex diffractometer). The diffraction pattern was scanned from 10◦ to 90◦ (2) using  Cu K␣ = 1.54178 Å and a step length of 0.02◦ (2). The grain size of crystallized alumina was estimated from the full width at half-maximum values of the X-ray diffraction using Scherrer’s formula. 3. Results and discussion The first point of interest was to investigate the efficiency of ECEF in improving the water quality for an industrial application in cooling towers. The second point concerned the capacity of ECEF to disinfect surface waters. 3.1. Removal of chemical species The efficiency of the ECEF process on the chemical composition of river water and pond water is given in Table 2. The experiments were carried out at 17 ◦ C with a river water having initial pH = 7.60

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Table 2 Removal efficiency of ECEF treatment applied to surface water and drinking water. Chemical parameters (conductivity)

Removal efficiencies (%) CAT Chloride Total hardness Hardness Nitrate Phosphate TSS Permanganate index

River water (0.41 mS cm−1 )

Tap water Ca2+ : 150 ◦ F 1.7 mS cm−1

1 mS cm−1

71 0 1 0 2 78 – –

17 4 8 8 0 68 – 47

and a conductivity of 0.41 mS cm−1 and at 12.3 ◦ C with a pond water having initial pH = 6.94 and a conductivity of 0.55 mS cm−1 . In order to determine the influence of some water parameters on the ECEF process, we investigated the efficiency of the treatment applied to tap water after NaCl addition. The calculation of the chemical removal efficiency (RE%) was performed using formula (5) where C0 and C are concentrations of the chemical before and after electrolysis: RE (%) =

(C0 − C) × 100 C0

(5)

The results (Table 2) show a very good efficiency for orthophosphate ions and fairly good ones for the suspended solids, nitrate ions and the permanganate index. The nitrate removal efficiency was better for the pond water than for the river water probably because nitrate concentration was lower in the pond water. For tap water, and Ca2+ supplemented tap water, the results given in Table 2 show that higher conductivity and Ca2+ concentration have a negative effect on the phosphate ions removal. But, the high concentration of Ca2+ decreased the CAT. According to the results of Table 2, ECEF can be successfully used to remove suspended matters, orthophosphate and nitrate ions and organic matter involved in the permanganate index. After 30 min of electrolysis, about 50% of the suspended matters were precipitated. It is well known that the similar charge of colloidal particles prevent their aggregation through electrostatic repulsion. The ECEF efficiency is based on the fact that the instability of colloids, suspensions and emulsions is determined by electric charges. Therefore, when additional electrical charges are supplied to colloidal particles via appropriate electrodes, the surface charges are neutralized and several particles coalesce and lead to larger agglomerates which may be separated by flotation or sedimentation [21,35]. Holt et al. [23] proved that the electrolysis current is not the sole parameter which controls the coagulation process. Bubble production rate and fluid regime within the reactor are also key parameters of the process. The collision between particles, the floc growth and the potential for material removal by flotation are controlled by the current. Low electrolysis current produces low hydrogen bubble density, leading to a low upward momentum flux, and thus a poor mixing within the reactor. Under these conditions the sedimentation is more efficient than the flotation. When the current increases, the bubble density and the amount of mixing increase and favor flotation over sedimentation. The operational current has a strong influence on the dominant pollutant removal path, that is flotation or settling, and consequently on the floc production. High current means a small electrocoagulation cell but the process works with a wasting electrical energy in heating up the water [30]. The decrease of the total hardness can be attributed to an electrochemical generation of a softener to limit the scaling [36]. We should mention that the simultaneous presence of calcium ions

21 2 21 14 26 99 51 47

Pond water (0.55 mS cm−1 )

9 0 10 62 99 46 46

and hydrogen carbonate leads to the formation of calcium carbonate and hydrogen carbonate on the cathode according to reactions (6) and (7) [37]: HCO3 − + OH− → CO3 2− + H2 O CO3

2−

+ Ca

2+

→ CaCO3

(6) (7)

The reduction of the permanganate index is similar to results obtained in studies carried out on organic matter removal [38,39]. The nitrate removal results confirm the experiments that were carried out by Emamjomeh and Sivakumar [40] by a batch ECEF process. The nitrate removal efficiency depends on electrolysis time and current values. At both low current and short electrolysis time, the nitrate removal efficiency was very low. The important removal of phosphate ions is the most interesting result. During the dissolution of aluminum anode, micro-flocs are formed rapidly. After the electrocoagulation, the solutions were maintained unstirred for a few minutes in order to allow the agglomeration of micro-flocs into larger flocs. During this flocculation process all kinds of micro-particles and negatively charged ions are attached to the flocs by electrostatic bonding. Phosphate ions are also adsorbed onto coagulated flocs. When aluminum ions are present in the water, AlPO4 forms in the low pH range (<6.5) and at a higher pH range (>6.5) aluminum increasingly converts to oxides and hydroxides [41]. The removal of orthophosphate and nitrate ions is very important for the success of the process. Indeed, these ions are vital nutriments for a good bacterial development. Their removal inhibits biofilm formation. In order to understand the action of electrocoagulation against bacteria, we measured the oxygen concentration and the ORP of solution during some experiments. The results are presented in Figs. 1–3. When the electrocoagulation experiments were performed in the presence of chloride salts, the oxygen concentration showed a

Fig. 1. Variations of O2 concentration during electrocoagulation carried out in the presence of different electrolytes (electrolyte concentration 0.1 M; I = 0.5 A).

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Table 4 ATP (TCM) results for isolated solids after ECEF treatment of river water and pond water. Ref.

Fig. 2. ORP variation during an electrocoagulation carried out in KCl solution (0.1 M; I = 0.5 A).

Fig. 3. ORP variation during an electrocoagulation carried out in KNO3 solution (0.1 M; I = 0.5 A).

90% decrease within 10 min (Fig. 1). These oxygen removals were due to a deoxygenating action of the hydrogen evolved at the cathode. When the electrocoagulation was realized in the presence of nitrate salts, the oxygen removal was less efficient. A 90% decrease of oxygen concentration needed 60 min. During these electrolyses less hydrogen was evolved at the cathode since a part of the current was consumed by the nitrate reduction. Oxygen removal during electrocoagulation was more efficient than a deoxygenating process performed by a nitrogen bubbling into the solution. The oxygen decrease leads to an unfavorable environment for aerobic bacteria. Figs. 2 and 3 present the variations of ORP during electrocoagulations. As expected for a solution with decreasing concentration of oxygen removal and increasing content of hydrogen, the ORP decreased until −0.15 V/SCE. In agreement with a lower concentration of hydrogen, the potential decreased more slowly in nitrate solutions (Fig. 3). 3.2. Bacterial removal by ECEF The effect of ECEF on bacteria and algae development was investigated on treated waters. After 10 min of electrolysis, a foam layer appeared at the surface and increased in time as the result of elecTable 3 Efficiency of ECEF treatment on the bacteriological parameters for river water and pond water (measures by standard methods).

ATP total (pg mL−1 )

ATP extra (pg mL−1 )

ATP intra (pg mL−1 )

Dead cellular (%)

River water [1] 33,993 [2] 42,790 [3] 10,591

11,540 9879 5598

22,453 32,911 4993

34 23 53

Pond water [1] 31,777 [2] 26,349 [3] 18,909

17,968 26,310 17,404

3809 39 1505

57 100 92

troflotation. The bacteriological results after 30 min of electrolysis are listed in Table 3. They show a total elimination of flora and good disinfection efficiency. Ghernaout et al. [21] founded similar results with surface water using steel electrodes at the same voltage but with a current of 10 A. In our experiments, the current value was set at 0.22 A. This low current was taken in order to avoid a temperature increase due to a Joule effect. ATP was measured before and after electrocoagulation. ATP is a direct and interference-free indicator of total biomass. Any living cell produces and consumes ATP. This molecule is thus specific to a living cell and we can consider that any trace of ATP is the witness of cells which are died or live. Table 4 gathers ATP results obtained on the river and pond flocs. Table 5 contains results of solution analysis. We observed a significant fluctuation in results concerning the percentage of dead bacteria in the flocs. These differences can result from 10% of error expressed by LuminUltra technologies. ATP is not completely eliminated from died cells. However, we can suppose that all the bacteria did not die in the flocs. Concerning the measures of ATP QGA, results of Table 5 confirm the results obtained with a standard method. The solution was bacteria-free. Bacteria were trapped into the flocs and for most part of them they were living. The experiments reported indicate only that the bacteria are not detectable by any of classical cultivation or ATP methods (Tables 3 and 5). But a significant fraction of the initial population remains alive in the flocs (Table 4). To explain the dead and the concentration of bacteria in the flocs we used some working hypothesis. 3.3. Disinfection hypothesis by ECEF According to Oss [42] bacterial adhesion to surfaces results from the Lifshitz–Van der Waals free energy interaction and the Lewis acid–base free energy interaction. Bacteria either donate or accept electrons to the surface of the substrate (in this case the gas bubbles). Adhering bacteria may decrease electrostatic repulsion allowing floc formation. The charge transfer, however, takes place over a range shorter than 0.5 nm, so close contact is needed. Table 5 ATP results (QGA) for water obtained after ECEF treatment and decantation.

Experiment reference

ECEF 1

ECEF 2

ECEF 3

Ref.

ATP (pg mL−1 )

Equivalent microorganismes

% Removal

River water To (UFC mL−1 ) Tf (UFC mL−1 ) Percentage decrease (%)

1.12E+02 0 100

1.12E+02 0 100

1.12E+02 0 100

River water Blank Test 1 Test 2 Test 3

335.4 31.6 14.3 15.9

3.3E+05 3.1E+04 1.4 E+04 1.6 E+04

91 96 95

Pond water Blank Test 1 Test 2 Test 3

933.1 36.1 101.1 18.2

9.3E+05 3.6E+04 1.0E+05 1.8E+04

96 89 98

Experiment reference

ECEF 1

ECEF 2

Pond water To (UFC mL−1 ) Tf (UFC mL−1 ) Percentage decrease (%)

4.15 E+04 2.50 E+02 99.4

6.05 E+05 2.20 E+02 99.6

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attributed to smaller crystallites. From the X-ray diffraction data, the grain size of crystallites can be calculated using Scherrer’s formula (8), where d is the grain size,  is the X-ray wavelength, ˇ is the full width at half-maximum and  is the Bragg angle. Using Eq. (8) the grain size of AlOOH was estimated to be about 10–15 nm. So, the large rays of boehmite are due to nanocrystallites and that they may be involved in a bactericidal effect: d=

Fig. 4. Diagram of X-ray diffraction of solid compounds isolated at the end of an electrocoagulation (NaCl 0.01 M; I = 0.1 A). In the X-ray diffractogram, peaks attributed to a boehmite structure are marked with*.

This contact is realized easily in the electrocoagulation process where the negatively charged bacteria could electrophoretically move, resulting in higher bacteria concentrations near the positively charged anode. So, the coagulation creates a floc blanket that entraps colloidal particles as well as bacteria still remaining in the aqueous solution [43]. The inactivation of bacteria and yeast cells by electrochemical means has been well documented [31,44–47]. It is important to highlight that these studies describe the electrochemical process that are different from electocoagulation. In the following we can only make some hypothesis about the links. It has been reported that electrochemical and magnetic fields can destroy a wide variety of microorganisms from viruses [3] to bacteria [48,49]. It can be assumed that the current applied creates a potential difference from one extremity to the other of the cellular membrane on account of its electrical resistance. This potential difference modifies consequently the trans-membrane potential producing destruction of the cellular membrane. Usually, the membrane is constituted by a bi-layer of phospholipids and it protects vital centers of bacterial cells. Protein inclusions inside the membrane allow ionic change with the cell environment. A phospholipidic membrane is not easily oxidized whereas proteins are easily destroyed by the direct effect of an electric field. Cells cannot change more ions but can however be reactivated in a favorable environment. Its total destruction requires an oxidant capable of passing through the membrane and reaching vital centers [49,50]. Electric fields are also capable of destroying cells without destroying their membranes. Matsunaga et al. [51] describe a system in which cells are killed without rupturing, but rather with the electrochemical oxidation of an intracellular coenzyme A. Thus, electric fields may directly oxidize cellular constituents, leading to cell death. Comparisons of results from different authors have to be treated carefully because the inactivation efficiency of electrochemical disinfection systems is largely dependent on electrolytic cell configuration, the type of microorganism involved, as well as other experiment parameters, such as flow rate and current density [52]. During electrolysis, the removal of oxygen (Fig. 1) and the ORP variations (Figs. 2 and 3) could be unfavorable conditions for living aerobic bacteria. The solid compound which was isolated after electrolysis was studied by X-ray diffraction. The pattern (Fig. 4) exhibits two kinds of crystallites. The solid was a mixture of two identified alumina: bayerite Al(OH)3 and boehmite AlOOH. The larger peaks are attributed to a boehmite structure, and the sharper peaks are those of bayerite. The ray shape is significant of the crystallite size. Indeed, the Scherrer’s relationship [53,54] tells that larger rays are

0.9 ˇ cos 

(8)

Jiang et al. [55] proved that alumina nanoparticles exhibit a mortality rate of 36% towards Escherichia coli. Toxicity of nanoparticles was not only from the dissolved metal ions, but also from their greater tendency to attach to the cell walls than to aggregate together. Due to positive surface charges on the alumina nanoparticles at near-neutral pH, an electrostatic interaction is possible between negatively charged E. coli cells and the particles, leading to bacterial adhesion onto nanoparticles surfaces [55,56]. The results obtained prove that to separate the total flora of the effluent by using a simple decantation, an important current is not useful. This result would be interesting in the development of a water treatment process. 4. Conclusions The effects of disinfection by the ECEF process have been studied for the case of two raw surface waters. It was found that a total removal of bacteria and algae were rapidly reached in 30 min. The electrocoagulation supplies a robust packaging of nanoparticles susceptible to present some biocide properties. Electrocoagulation with aluminum electrodes is a suitable process for the removal of phosphate which is nutriment for bacteria, mushrooms and algae. ECEF can be a solution to treat the most common problem of phosphorus compounds involved in eutrophication. Electrocoagulation is an electrochemical technique with many applications, in which a variety of unwanted dissolved particles and suspended matter can be effectively removed from an aqueous solution by electrolysis. The hardness, nitrate and phosphate ions and TSS are decreased down in surface water. The electrocoagulation would allow to limit the use of biocides, and consequently to save chemicals and to decrease the operating costs of pretreatment stations. This technique would also allow to use surface waters as a supplement of air cooling towers and thus to protect natural resources. Acknowledgement Financial support from the Conseil Régional de Bretagne is gratefully acknowledged (by A.D. and D.H.; Project Prir Proelec no 509). References [1] P. Drogui, S. Elmaleh, M. Rumeau, C. Bernard, A. Rambaud, Hybride process, microfiltration–electroperoxidation for water treatment, J. Membr. Sci. 186 (2001) 123–132. [2] C. Fersi, L. Gzara, M. Dhahbi, Treatment of textile effluents by membrane technologies, Desalination 185 (2005) 399–409. [3] B. Zhu, D.A. Clifford, S. Chellam, Comparison of electrocoagulation and chemical coagulation pretreatment for enhanced virus removal using microfiltration membranes, Water Res. 39 (2005) 3098–3108. [4] A. Bagga, S. Chellam, D.A. Clifford, Evaluation of iron chemical coagulation and electrocoagulation pretreatment for surface water microfiltration, J. Membr. Sci. 309 (2008) 82–93. [5] E. Friedler, I. Katz, C.G. Dosoretz, Chlorination and coagulation as pretreatments for greywater desalination, Desalination 222 (2008) 38–49. [6] X.M. Chen, G.H. Chen, P.L. Yue, Separation of pollutants from restaurant wastewater by electrocoagulation, Sep. Purif. Technol. 19 (2000) 65–76. [7] M.Y.A. Mollah, R. Schennach, J.R. Parga, D.L. Cocke, Electrocoagulation (EC)—science and applications, J. Hazard. Mater. B 84 (2001) 29–41.

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