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REMEDIATION OF HEAVY METAL BEARING WASTEWATER BY PHOTOVOLTAIC 

ELECTROCOAGULATION 

Konstantinos Dermentzis, Dimitrios Marmanis, Achilleas Christoforidis 

Department of Petroleum & Natural Gas Technology, Kavala Institute of Technology, 65404 Agios Loucas, 

Kavala, Greece Tel +30 2510 245133, Fax: +30 2510 245133 E-mail: demerz@otenet.gr 

Abstract 

In this study a photovoltaic electrocoagulation (PV-EC) process is proposed, which combines the 

autonomous and environmentally friendly photovoltaic solar energy with the capability of iron 

electrocoagulation to effectively remove heavy metals, such as chromium, nickel and copper from industrial 

electroplating effluents. The photovoltaic array can be connected directly to the electrocoagulation reactor 

without batteries increasing, in this way, the system sustainability and eliminating the environmental threat of 

improper battery disposal. The PV-EC system is made versatile according to the instantaneous solar 

irradiation by adjusting the wastewater flow rate to the current intensity supplied by the photovoltaic array. All 

operating parameters affecting the efficiency of the proposed process, such as wastewater conductivity, pH, 

flow rate, current density, electroprocessing time and solar irradiance were studied and optimal conditions 

were investigated. The experimental results showed that by applying a current density of 30 mA/cm2the 

concentrations of chromium, nickel and copper in the treated electroplating wastewater were effectively 

reduced from their corresponding initial values of 86, 65 and 37 mg/L to less than the permissible limit, 

amounting to a removal percentage of over 99%. The corresponding electrical energy consumption was 15 

kWh per m3 of treated wastewater. The proposed process is appropriate for remediating industrial effluents 

laden with heavy metals and especially for applications in remote and isolated locations without connection 

to the public electrical system. 

Keywords: electrochemical coagulation; electroplating effluents; chromium; nickel; copper; 

photovoltaic solar energy

1. INTRODUCTION

Industrial effluents originating mainly from electroplating industries contain high amounts of heavy 

metal ions (Cr, Ni, Cu, Cd, Zn). These heavy metal bearing wastewaters are of considerable concern because 

they are non-biodegradable, highly toxic and probably carcinogen. Only 30-40% of all metals used in plating 

processes are effectively utilized i.e. plated on the articles. The rest contaminates the rinse waters during the 

plating process when the plated objects are rinsed upon removal from the plating bath.

Several treatment processes have been suggested for the removal of heavy metals from aqueous 

waste streams, such as adsorption (Kyzas et al., 2009), biosorption (Farhan et al., 2012), ion exchange 

(Inglezakis et al., 2003), cathodic reduction (Formari and Abbruzzese, 1999), electrodialysis/ 

electrodeionization using membranes (Arar et al., 2014; Caprarescu et al., 2011; Ren et al., 2013) or 

electrostatic shielding (Dermentzis, 2010), chemical coagulation - precipitation and electrocoagulation 

(Dermentzis et al., 2011; Verma et al., 2013). 

The conventional chemical coagulation relies on the decrease of the net surface charge and the 

electrical double-layer of colloids by the addition of coagulants, such as FeCl3, Al2(SO4)3, or organic 

polyelectrolytes which leads to their coagulation and precipitation.

Electrocoagulation is a new alternative way of coagulation, where the coagulants Al(OH)3 and 

Fe(ΟΗ)3 are not added to the treated solution but are produced in situ by electrodissolution of sacrificial 

anodes made of aluminum or iron respectively.

During the electrocoagulation process with iron electrodes the chemical reactions (1), (2) and (3) 

occur. The electrochemically produced Fe2+ and Fe3+ ions combine with OHions forming the needed 

coagulants Fe(OH)2 and Fe(OH)3 according to reactions (4) και (5). 

Fe 

 Fe2+ + 2e (anode) (1) 

 

Fe 

 Fe3+ + 3e (cathode) (2) 

2H2O + 2e 



H2 + 2OH-

(cathode) (3) 

 

2

nd International Conference - Water resources and wetlands. 11-13 September, 2014 Tulcea (Romania); Available online at 

http://www.limnology.ro/water2014/proceedings.html;

Editors: Petre Gâştescu ; Włodzimierz Marszelewski ; Petre Bretcan; ISSN: 2285-7923; Pages: 257-262; 

Open access under CC BY-NC-ND license ; 
258

Fe2+ + 2OH-Fe(OH)2 (4)

 

Fe3+ + 3OH-Fe(OH)3 (5) 

 

The Fe2+ ions can reduce Cr(VI) to Cr(III), while they are oxidized to Fe3+ ions according to reaction (6): 

CrO4

2-

 + 3Fe2+ + 4H2O + 4OH-  3Fe(OH)3 + Cr(OH)3 (6)

Cr(VI) ions are also reduced to Cr(III) ions at the cathode according to reaction (7): 

Cr2O7

2-

 + 6e- + 7H2O 

 3Cr3+

 + 14OH- (7)

Bivalent heavy metal ions Me2+ (Cu2+ and Ni2+) and trivalent chromium ions (Cr3+) are removed by 

adsorption by the coagulants Fe(OH)2 and Fe(OH)3. Furthermore, they combine with the electrochemically 

(reaction 3) or chemically (reaction 7) generated OH- ions and precipitate as insoluble hydroxides according 

to reactions (8) and (9) or: 

Me2+ + 2OH-Me(OH)2 (8)

 

Cr3+ + 3OH- Cr(OH)3 (9)

Both phenomena act synergistically leading to a rapid removal of heavy metal pollutants from water. 

The electrochemical coagulation process has the advantage of combined phenomena of oxidation, 

reduction, flotation, adsorption and coagulation. It is effectively applied to treatment of dye house effluents, 

oil wastes, paper mill and heavy metal bearing effluents. 

Increased environmental pollution and social concern about the environment in the last decades have 

led to the development of new renewable energy forms. The photovoltaic (PV) solar energy is one of the 

most popular and well studied renewable energy sources, which, as autonomous and environmentally 

friendly, is appropriate for small applications and especially in remote and isolated locations with lack of 

electric grid (Irfan, 1997). Electrochemical processes directly powered by photovoltaic energy have been 

recently reported in literature (Alvarez-Guerra et al., 2011; Ortiz et al., 2007; Valero et al., 2008; Zhang et 

al., 2013). As we are aware, none of them deals with heavy metal removal from industrial effluents. 

The present paper demonstrates the possibility of remediating heavy metal bearing electroplating 

effluents using electrocoagulation (EC) with iron electrodes, which is directly powered by a PV array 

without batteries. The photovoltaic electrocoagulation (PV-EC) system is made versatile according to the 

instantaneous solar irradiation by adjusting the wastewater flow rate to the current density supplied by the 

PV array. All operating parameters affecting the PV-EC process, such as wastewater pH, current density, 

conductivity, flow rate, contact time and solar irradiation are determined. 

2. METHODS

The actual wastewater was obtained from an electroplating unit located near Thessaloniki, northern 

Greece, with the main characteristics listed in Table 1. 

Table 1. Main characteristics of electroplating wastewater 

Parameter: Value:

pH 4.5

Conductivity 4500 μS/cm (after addition of KCl)

Cr (VI) mg/L 86 

Ni (II) mg/L 65 

Cu (II) mg/L 37 

The photovoltaic module used was SUNPOWER (Maxeon Cell Technology) SPR-327NE-WHT-D 

made from monocrystalline silicon with a surface area of 1.63 m2 and a peak power of 327 W. The 
259

experiments were conducted in Kavala Institute of Technology (latitude 40 ̊ 55 ́, longitude 24 ̊ 22 ́ and 

altitude 138 m above the sea level).

DC voltage and current were measured by a multimeter (PHYWE). Conductivity was measured by 

means of a conductometer (WTW). The pH and the temperature were measured using a Hanna pH-meter. 

The wastewater was circulated by a peristaltic pump. 

Electrolyses were conducted at room temperature in a cylindrical glass cell of 400 ml in which 200 

ml of wastewater were placed and slowly stirred with a magnetic bar at 500 rpm. Three commercially 

obtained iron plates of size 10cm x 5cm x 0.2cm immersed to a 6 cm depth with an effective area of 30 cm2 

each, were used as electrodes in the experiments. The inter-electrode distance was 0.5 cm. To remove the 

oxide and passivation layer from iron surface the electrodes were grinded with sandpaper and energized by 

dipping them in HCl 5N for 1 minute. KCl was added to every treated solution for prevention of passivation 

on the iron electrode surface and decrease of the excessive ohmic drop in the solution. Samples were 

extracted every 5 minutes, filtered using Whatman filter paper (Grade 40). The residual heavy metal ion 

concentrations were determined by Atomic Absorption Spectroscopy AAS (Perkin Elmer 5100). 

Figure 1 shows a flow diagram of the proposed PV-EC process. 

Figure 1. Diagram of the experimental setup. 1. PV Solar module 2. Regulator 3. Electrocoagulation reactor 

4. Electrode (a) 5. Electrode (b) 6. Filter 7. Treated solution 8. Flow meter 9. Peristaltic pump 10. 

Wastewater deposit 

3. RESULTS AND DISCUSSION

3.1. Effect of operating parameters 

The PV-EC process is affected by several operating parameters, such as initial pH, current density, 

conductivity, flow rate and contact time. In the present study all these parameters have been explored in 

order to evaluate a treatment technology for chromium, nickel and copper removal from actual electroplating 

wastewaters. 

3.1.1. Effect of initial pH 

The initial pH value of the treated solution has a considerable effect on the efficiency of the 

electrocoagulation process. Experiments were conducted in the pH range 2-10 using separate solutions of 50 

mg/L of copper, nickel and chromium respectively. As can be seen in Figure 2, after the electrolysis time of 

20 minutes at constant current density of 10 mA/cm2 the percent removal of all studied metals increases 

considerably with increasing pH in the range 2-10. In acidic environment (pH<2) the removal is low, 

whereas it increases considerably at pH 4 and is maintained high in the pH range 4-10. The decrease of 

removal efficiency in strong acidic medium is due to the formation of the soluble Fe2+ and Fe3+ ions which, 

as known (Adhoum et al., 2004; Vasudevan et al., 2009), do not favor the coagulation phenomenon. 
260

Figure 2. Removal of Cr, Ni and Cu by electrocoagulation versus initial solution pH

3.1.2. Effect of current density 

It is well known that the current density determines the coagulant dosage rate, the bubble production 

rate and size and the flocs growth resulting in a faster removal of pollutants. Measurements were carried out 

at different current densities 10-30 mA/cm2, at constant initial heavy metal concentrations of 96, 65, 37 

mg/L for Cr, Ni, Cu respectively and initial pH 4.5. According to Table 2, the removal rate of all studied 

metals increased, as expected, with increasing current density. In 70, 40 and 30 minutes of electrolysis time 

at the corresponding current densities of 10, 20 and 30 mA/cm2, chromium, nickel and copper ions have 

been almost quantitatively removed (>99%) and their concentration fell under the admissible limits for 

effluents discharge to sewage systems (2 mg/L). 

Table 2. Concentration variation of chromium, nickel and copper ions with time at different current densities

10 mA/cm2

Concentration (mg/L)

20 mA/cm2

Concentration (mg/L)

30 mA/cm2

Concentration (mg/L)

Time (min) Cr Ni Cu Cr Ni Cu Cr Ni Cu

0 86.0 65.0 37.0 86.0 65.0 37.0 86.0 65.0 37.0

10 44.5 32.6 19.3 23.5 16.1 8.4 14.5 8.1 5.5

20 17.3 14.4 7.7 7.6 4.0 3.3 1.4 0.3 0.2

30 8.8 6.8 2.3 1.2 0.3 0.2 0.1

40 4.2 2.5 0.4 0.3

50 2.6 0.7

60 0.8 0.3

70 0.2

3.1.3. Effect of conductivity 

The wastewater conductivity affects immediately the applied voltage and therefore the electrical 

energy consumption. The removal percentage of all studied heavy metals is hardly affected and remains 

constant over 99 % for the three tested wastewater conductivities of 1500, 3000 and 4500 μS/cm (Table 3).

Table 3. Electrocoagulation results for different wastewater conductivities 

Removal percentage (%)

Conductivity

(μS/cm)

Voltage 

(V)

Energy 

consumption

(kWh/m3

Cr Ni Cu

1500 18.4 64.6 99.3 99.0 99.4

3000 9.5 32.2 99.6 99.3 99.5

4500 5.2 15.0 99.4 99.2 99.1
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3.1.4. Effect of flow rate 

The current density supplied by the PV array depends on the solar irradiation and the temperature of 

the PV modules. These parameters cannot be controlled and will change continuously through the hours in a 

day or suddenly through clouds crossing or changes in wind speed. Ortiz et al. 2007 and Valero et al. 2008 

proposed a clever mode of operation in order to make the PV-EC system versatile to instantaneous solar 

irradiation by keeping constant the ratio current density/flow rate. Thus, when the current density supplied by 

the PV array changes, also the working flow rate must proportionally change to maintain this ratio constant. 

This operation way implies that the volume of treated wastewater is directly related to the solar energy 

incident on the panels. The experiments with constant current density and flow rate were conducted at a 

sunny midday and in short periods to keep approximately constant values of solar irradiation. As can be 

obtained from Table 4, by increasing the current density the cell voltage and flow rate increase 

proportionally, while the residence time decreases. The removal percentage of all three studied metals is 

hardly affected and remains high >99 % in all experiments. 

Table 4. Electrocoagulation results for different wastewater flow rates 

Removal percentage (%)

Flow rate

(L/h)

Current 

density

(mA/cm2)

Voltage

(V)

Residence 

time

(min)

Cr Ni Cu

0.3 10 8.4 40 99.7 99.2 99.5

0.6 20 16.2 20 99.4 99.1 99.3

0.9 30 24.6 13.3 99.3 99.0 99.1

3.2. Solar irradiation and I-V curve of photovoltaic module 

The solar irradiation intensity depends on the occasional meteorological/geographical conditions and 

influences the photovoltaic output current and therefore, the performance of the electrocoagulation process. 

As stated in section 3.1.4, the flow rate of the treated wastewater can be used as the control parameter. The 

most important characteristics of the current-voltage curve of the photovoltaic module for a solar irradiation 

of 1000 w/m2 and temperature of 25C are given in Figure 3. The short circuit current Isc is the maximum 

current supplied by the PV panel at zero voltage between terminals. It depends mainly on solar irradiation 

and amounts to 6.46 Ampere. The open circuit voltage is the maximum voltage reached in absence of load. It 

depends mainly on temperature and amounts to 64.9 Volt. 

4. CONCLUSIONS 

This paper shows the feasibility of performing remediation of heavy metals (Cr, Ni, Cu) bearing 

electroplating effluents by directly connecting the electrocoagulation reactor to the photovoltaic generator. 

The current density supplied by the PV array depends on the solar irradiation and the temperature of the 

photovoltaic modules. However, the PV-EC system is made versatile to instantaneous solar irradiation by 

adjusting the flow rate of the treated wastewater and keeping constant the ratio current density/flow rate. The 

removal percentage of chromium, 

nickel and copper remains high (>99 

%) for the three tested wastewater flow 

rates of 0.3, 0.6 and 0.9 L/h and the 

three wastewater conductivities of 

1500, 3000 and 4500 μS/cm. Based on 

the experimental results, the proposed 

PV-EC process could present some 

advantages for wastewater purification 

applications in isolated places with lack 

of electric grid. Furthermore, the 

process avoids problems concerning 

the maintenance of batteries and 

increases the system sustainability. Figure 3. I-V curve of photovoltaic module
262

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