665_ftp

Arash Dalvand1

Mitra Gholami1

Ahmad Joneidi1

Niyaz Mohammad Mahmoodi2

1Department of Environmental Health

Engineering, Tehran University of

Medical Sciences, Tehran, Iran2Department of Environmental

Research, Institute for Color Science

and Technology, Tehran, Iran

Research Article

Dye Removal, Energy Consumption and OperatingCost of Electrocoagulation of Textile Wastewateras a Clean Process

In this research, the efficiency of electrocoagulation treatment process using

aluminum electrodes to treat synthetic wastewater containing Reactive Red198

(RR198) was studied. The effects of parameters such as voltage, time of reaction,

electrode connection mode, initial dye concentration, electrolyte concentration, and

inter electrode distance on dye removal efficiency were investigated. In addition,

electrical energy consumption, electrode consumption, and operating cost at optimum

condition have been investigated. The results showed that dye and chemical oxygen

demand removals were 98.6 and 84%, respectively. Electrode consumption, energy

consumption and operating cost were 0.052 kg/m3, 1.303 kWh/m3 and 0.256US$/m3,

respectively. Dye removal kinetic followed first order kinetics. It can be concluded that

electrocoagulation process by aluminum electrode is very efficient and clean process

for reactive dye removal from colored wastewater.

Keywords: Aluminum electrode; Clean process; Dye removal; Electrocoagulation; Energyconsumption

Received: June 23, 2010; revised: July 3, 2010; accepted: September 20, 2010

DOI: 10.1002/clen.201000233

1 Introduction

Textile industries consume large amounts of water and produce

colored wastewater [1–11]. Thus, using the appropriate wastewater

treatment method, to recycle the consumed water is necessary. In

the recent years, worldwide consumption of textile dyes increased

annually and worldwide production of dyes over 700 000 tons per

years were estimated [10]. Textile industries use more than 10 000

dyes and pigments for dyeing natural and synthetic fibers [12, 13].

Presence of dyes in water resources and aqueous environments,

beside aesthetic aspect [14, 15], affect the transparency and gas

solution in water [16] and some of these dyes are toxic, mutagenic

and carcinogenic to human and aquatic life [13, 17–19]. Also dis-

charge of colored wastewater without adequate treatment interferes

with light penetration [14] that disturbs biological processes and is

harmful for aqueous plants.

Usually, dyes contain aromatic rings in chemical structures [10,

20] and therefore, have high stability against light, oxidants, and

biological degradation [10]. Thus reduction of dye and chemical

oxygen demand (COD) from textile wastewaters are difficult [21].

Reactive dyes are widely used to color cellulose fibers such as

cotton [22]. Cotton is the most widely used fiber in textile industry.

Due to hydrophilic properties of reactive dyes [22, 23], reactive

dyes are not absorbed onto biomass to any great degree [15] and

generally pass through conventional biological wastewater

systems.

There are various kinds of physical, biological, and chemical

processes to remove dyes from colored wastewater [1–29]. Most

of the treatment methods have disadvantages. Regeneration of

adsorbents is difficult [27, 28]. Chemical coagulation needs

to additional chemicals to wastewater and produces large

amounts of sludge, which needs to be disposed [11]. The costs

of advanced oxidation processes such as UV/H2O2, ozonation,

and photo catalysis is high and are not economically feasible

[29, 30]. Chemical oxidation by chlorine is very effective method,

but it produces toxic by products such as organochlorine

compounds [12].

The most of reactive dyes are toxic to microorganisms, recalci-

trant, and resistant to biological degradation. Therefore convention-

al biological treatment methods have low efficiency to treat these

dyes [10]. Thus, using an efficient method to remove reactive dyes

from colored wastewater is necessary.

In the recent years, many researches on the application of electro-

chemical processes have been studied to remove pollutants from

aqueous solutions [31–46]. Electrochemical treatment method is an

eco-friendly and cost-effective method [34]. Among electrochemical

treatments, electro-oxidation and electrocoagulation are more

effective than the others to remove dye from textile wastewaters

[22, 28]. Main mechanisms of pollutant removal during electrocoa-

gulation are including coagulation, adsorption, precipitation, and

flotation [28]. Electrocoagulation treatment has advantages such as

smaller space in compare to biological treatments due to shorter

reaction time [13, 30], low sludge production in compare to chemical

coagulation [23], low cost of equipment and operation and easy

operation [17, 47].

Correspondence: Dr. N. M. Mahmoodi, Department of EnvironmentalResearch, Institute for Color Science and Technology, Tehran, Iran.E-mail: [email protected]

Abbreviations: COD, chemical oxygen demand; RR198, Reactive Red198;H2, hydrogen gas.

Clean – Soil, Air, Water 2011, 39 (7), 665–672 665

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com

During electrocoagulation, coagulants are generated in situ by the

electrooxidation of sacrificed anodes. Then aluminum or iron

hydroxide flocs destabilize and aggregate the suspended particles

or precipitates and adsorb dissolved contaminants [29]. Aluminum

and iron are most commonly used materials to electrocoagulation,

because these materials are low cost and readily available [17].

In this research, efficiency of electrocoagulation treatment using

aluminum electrodes to remove Reactive Red198 (RR198) from

aqueous solution has been investigated. The effects of parameters

such as voltage variation, time of reaction, inter electrode distance,

initial dye concentration, electrolyte concentration, and electrode

connectionmode on dye removal percentage have been evaluated. In

addition, optimum operation condition in view of electrical energy

consumption and electrode consumption were studied.

2 Material and methods

Reactive Red198 (RR198) was purchased from Hoechst Company

(Germany). The properties of RR198 are shown in Tab. 1. All reagents

were obtained from Merck Company.

Dye concentration was determined by measuring of dye absor-

bance at maximum wavelength using a UV–visible spectropho-

tometer (CECIL7001, England) according to standard method for

examination of water and wastewater [48]. The COD was measured

by the standard method (method 5220b). pH was measured by pH

meter (HACH HQ, USA). A digital multimeter (DEC-RE330Fc, Taiwan)

was used to measure the voltage and current. For conducting

of experiments, a rectangular tank with dimensions of 14 cm

(length)� 12 cm (width)� 14 cm (height) wasmade. Working volume

of reactor was 2 L. Four electrodes (2 anodes and 2 cathodes)

were made from aluminum plates. Dimensions of each electrode

were 11.2 cm (length)� 10.8 cm (width)� 0.2 cm (thick). Total active

area of electrodes was 484 cm2.

Electrodes were connected to a DC power supply (micro-Iran, 0–

40V, and 0–5A) in monopolar or bipolar mode. Then, 2 L synthetic

wastewater containing specific amount of dye was fed into the

reactor (pH: 5.5 and conductivity 45mS/cm). For each run, Voltage

was held constant at 5, 20, or 40V and current variation was

measured continuously during the process. The reactor contents

were mixed continuously by a magnetic stirrer. During the process,

samples were withdrawn from the reactor at different contact times

of 5, 15, 30, 45, 60, 75, and 90min and settled for a time of 30min,

centrifuged (4000 rpm, 5min) and analyzed. All experiments were

carried out in a batch mode. After each run, electrodes were dipped

in HCl (1.3M) for 30min, rubbedwith a plastic brush and rinsed with

water and dried. Experiments were performed at 208C.The percentage of dye removal, COD removal and electrical energy

consumption were determined according to Eqs. (1), (2), and (3),

respectively:

h ¼ ½ðC0 � CÞ=C0� � 100 (1)

h ¼ ½ðCOD0 �CODÞ=COD0� � 100 (2)

E ¼ ðU I tÞ=V (3)

where h is dye and COD removals (%). C0 and C are dye concentration

before reaction after reaction (mg/L), respectively. COD0 and COD are

chemical oxygen demand before and after reaction (mg/L), respect-

ively. E, U, I, t, and V are electrical energy consumption (kWh/m3),

voltage (V), current (A), time of reaction (h), and the volume of

solution (L), respectively.

3 Results and discussion

3.1 Effect of time and voltage on dye removal

The effect of time and voltage on dye removal efficiency is given in

Fig. 1. As shown in this figure, when voltage increased from 5 to 40V

during 30min, dye removal percentage increased from 83.4 to 99.9%.

Also, with increasing time of reaction from 5 to 90min at constant

voltage, dye removal gradually increased. The results show at first

5min of reaction, dye removal efficiency is low but with increasing

reaction time, efficiency increased. With increasing time of reaction

from 5 to 90min at constant voltage (20 V), dye removal increased

from 55.27 to 100%, respectively. Voltage and time of reaction are

two major operation parameters that determine the coagulant

dosage rate during electrocoagulation.

Three main processes which occurred during electrocoagulation

include:

(1) Electrolytic reactions at surface of electrodes;

(2) Formation of coagulants in aqueous phase;

(3) Adsorption of soluble or colloidal pollutants onto coagulants and

removal of them using sedimentation or flotation of flocs

when H2 bubbles were produced at the cathode [47].

Table 1. Properties of Reactive Red198.

Dye Reactive Red198

Chemicalstructure

NN

N OH

SO3NaNaO

3S

NH

Cl

NH

NaO3S

N N

SO2CH

2CH

2OSO

3Na

Chemicalformula

C27H18ClN7O16S5Na4

Molecularweight (g/mol)

983.5

lmax (nm) 518 Figure 1. Effect of voltage on dye removal during electrocoagulation(interelectrode distance: 1 cm, pH 5.5, and dye: 50mg/L).

666 A. Dalvand et al. Clean – Soil, Air, Water 2011, 39 (7), 665–672


Two main mechanisms of reactions that occur at cathode and

anode during electrocoagulation with aluminum electrodes pro-

duce coagulants (Eqs. (4)–(6)) [36, 47]:

Anodic reaction:

Al ! Al3þ þ 3 e� (4)

Cathodic reaction:

3H2Oþ 3 e� ! 3OH� þ 3=2H2ðgÞ (5)

Overall reaction:

Alþ 3H2O ! AlðOHÞ3ðsÞ þ 3=2H2ðgÞ (6)

Hydrogen gas (H2) and hydroxyl ions are produced at cathode due

to reduction of water and main product of anodic reaction is

aluminum ion. The released ions neutralize the particle charges

and thereby initiate coagulation. Also hydrogen ions produced at

cathode during reduction of water react with aluminum ions and

producemonomeric and polymeric species of aluminumhydroxides.

These products are able to remove dye from wastewater either by

complexation or by electrostatic attraction, that followed by coagu-

lation [29, 36]. In surface complexation, the pollutants act as ligands

(dyes) to chemically bind hydrous aluminum.

Dye-Hþ ðOHÞOAlðsÞ ! Dye-OAlðsÞ þ H2O (7)

Dye and COD removals depend on dosage of aluminum, and

dosage of coagulant depends on time of reaction and voltage. So,

while one of two parameters increases, production of coagulants and

flocs increase and pollutants are removed.

3.2 Effect of inter electrode distance on dye

removal

The effect of distance between anode and cathode on dye removal at

constant voltage (20 V) was studied at 1, 2, and 3 cm. As shown in

Fig. 2, when inter electrode distance increases from 1 to 3 cm, dye

removal efficiency decreases from 98.59 to 90.43% after 30min

electrolysis at 20V, respectively. It can be attributed that with

increasing of distance between electrodes at constant voltage, elec-

trical resistance between electrodes increases and current passed

through electrodes decreases. The decreasing of current, lead to

lower production of aluminum and hydroxyl ions and dye removal

efficiency decreases. Results showed that with an increasing of gap

between electrodes, electrical energy consumption decreased. On

the other hand, with increasing of inter electrode distance, less

interaction of the dye with the hydroxyl polymers is expected, thus

local concentration and electrostatic attraction would decrease and

dye removal efficiency reduces [22].

3.3 Effect of time and voltage variations on

electrical energy consumption

Dye removal percent and energy consumption were considered to

determine an optimized voltage, time and inter electrode distance.

The effects of voltage and time on electrical energy consumption

were given in Fig. 3. Results showed that with increasing reaction

time from 5 to 90min electrical energy consumption linearly

increases from 0.25 to 3.31kWh/m3 wastewater at 20V and 1 cm

of interelectrode distance. At all inter electrode distances, electrical

energy consumption at 40 V was approximately four times higher

than that of 20 V. Thus 20V is preferred to 40V due to high dye

removal efficiency and low electrical energy consumption. In

addition, Fig. 3 showed that at 20V maximum dye removal equal

to 100% was achieved after 75min, while dye removal was 98.59% at

30min. Electrical energy consumption at 75min was 2.17 times

higher than that of 30min. Thus optimum operational condition

was voltage: 20V, inter electrode distance: 1 cm and reaction time:

30min.

3.4 Effect of voltage variations on final pH of

effluent during electrocoagulation

The pH is one of the important parameters that affect the electro-

coagulation process. Former studies demonstrate that highest treat-

ment efficiencies are obtained at pH 5–6 during electrocoagulation

using aluminum electrodes [14]. Initial pH of dye solution used in

this research was 5.5. Thus this parameter was not assessed in this

study and only effects of voltage and time on final pH of effluent

during process were evaluated.

Figure 2. Effect of interelectrode distance on dye removal (20V, pH 5.5,and dye: 50mg/L).

Figure 3.Effect of voltage on electrical energy consumption (interelectrodedistance: 1 cm).

Clean – Soil, Air, Water 2011, 39 (7), 665–672 Electrocoagulation of Textile Wastewater 667


As can be seen in Fig. 4, with increasing of voltage from 5 to 40V

and time from 5 to 90min, final pH of effluent and electrical energy

consumption increased. This leads to increase of anodic and cathodic

reactions, thus water reduction at cathode extremely enhanced and

amount of hydroxyl ions gradually increased. On the other hand rate

of hydrogen ion evolution in form of H2 gas from the solution

increased [18, 20]. Thus pH of effluent gradually increased from

5.5 to 8.7 during reaction. After 30min of reaction, pH was already

constant at all voltages, because at high pH, metal hydroxide of

Al(OH)3 reacted with hydroxide ions and produced Al(OH)4� [49].

Thus, when aluminum electrodes were used for electrocoagulation,

standard pH to discharge of effluent in water sources can be

provided without pH neutralization.

3.5 Effect of initial dye concentration on dye and

COD removal

To determine influence of initial dye concentration on dye and COD

removals efficiencies during electrocoagulation, five dye solutions

with different initial dye concentrations (50, 75, 100, 200, and

300mg/L) were treated at optimum condition (20V, inter electrode

distance of 1 cm and 30min reaction time). Results showed that

when dye concentration increased from 50 to 300mg/L, dye and

COD removals efficiencies reached 98.59 to 69.45% and 84.1 to 56.2%,

respectively (Fig. 5). One of the most important pathways of dye

removal by electrocoagulation is adsorption of dye molecules on

metallic hydroxide flocs. According to Faraday’s low, a constant

amount of Al3þ released to the solution at same current, voltage,

and time for all dye concentration. Thus same amount flocswould be

produced in the solution. The adsorption capacity of flocs is limited

and specific amount of flocs is able to adsorb specific amount of dye

molecules [22]. So, with increasing of dye concentration, amount of

produced flocs is insufficient to adsorb all dye molecules, therefore

dye and COD removal decreases.

3.6 Effect of electrolyte concentration on dye

removal

Sodium chloride was used as an electrolyte at different concen-

trations (0, 0.25, 0.5, and 1mM) to investigate the effect of electrolyte

concentration on dye removal during electrocoagulation process at

optimumoperational condition (20V, 1 cm, 30min). Figure 6 showed

with increasing of electrolyte concentration from 0 to 1mM, after

5min contact time dye removal efficiency increased from 55.3 to

96.5%. Also with increasing of electrolyte concentration from 0 to

1mM, the required time to reach to 98.5% dye removal percentage,

decreases from 30 to 10min. Thus at constant voltage with increas-

ing of electrolyte concentration, required time to reach a specific dye

removal efficiency would be decreased. It can be attributed that at a

constant voltage with increasing of electrolyte concentration, con-

ductivity of dye solution increases (conductivity of solutions rise

from 44 to 168mS/cm when NaCl concentration increased from 0 to

1mM) and resistance decreases, so the passed current increases

and the produced amount of metallic hydroxide and dye removal

increases. Results showed that when electrolyte concentration was

increased from 0 to 1mM, electrical energy consumption increased

from 0.46 to 1.5 kWh/m3 synthetic wastewater and with increasing

of electrical energy consumption, floc production rate increased

and dye removal efficiency enhanced. In addition, the presence

of NaCl in solution causes the production of hypochlorite ion at

anode and leads to increase dye removal by oxidation of dye

molecules.

Figure 5. Effect of initial dye concentration on dye and COD removals(interelectrode distance: 1 cm, 20V, and time: 30min).

Figure 4. Effect of voltage on final pH of effluent during electrocoagulation(interelectrode distance: 1 cm).

Figure 6.Effect of electrolyte concentration on dye removal (interelectrodedistance: 1 cm, 20V, pH 5.5, dye: 50mg/L).



3.7 Effect of electrode connection mode

To determine the effect of electrode connection mode on dye

removal percentage in optimum condition, experiments were per-

formed in three configurations of monopolar parallel (mp-p), mono-

polar series (mp-s), and bipolar. Figure 7 showed that monopolar

parallel connection mode was the most effective connection mode

for dye removal. At operating time of 30min, dye removal was 98.59,

91.18, and 84.6% for mp-p, mp-s, and bipolar, respectively. Highest

dye removal of 100% was achieved when mp-p connection mode was

used after 60min reaction time. While highest dye removal percent-

age at mp-s and bipolar connections were 97.6% and 95.7%, respect-

ively, after 90min reaction time. It was attributed that at constant

voltage in the mp-p connection mode higher current through elec-

trodes passed than other connections. Consequently, this connec-

tion mode causes to release more Al3þ ions and hydroxyl ions and

produces more flocs and is able to remove more dye molecules in

comparison to other connections.

3.8 Effect of current efficiency

Current efficiency is an important parameter that affects the life-

time of the electrodes during electrocoagulation process [19]. The

ratio of the experimental Al dosage (DMexp) to the theoretical value

(DMtheo) is defined as the current efficiency (w). This parameter is

calculated using the following equation:

’ ¼ ðDMexp=DMtheoÞ � 100 (8)

The amount of theoretical aluminum dissolution can be calcu-

lated according to Faraday’s law using the following equation:

Alþ3theoretical ¼ ðM I tÞ=ZF (9)

whereM, I, t, Z, and F are molecular mass of aluminum (26.98 g/mol),

the electrical current (A), time of reaction (s), the number of electron

moles (¼ 3), and Faraday’s constant (¼ 96487 c/mol), respectively.

The experimental Al dosage was determined by weighting of

electrodes before and after each run and weight loss of aluminum

was calculated. The results showed that the actual consumption of

the electrodes was 0.104 g after 30min of process at average current

of 0.26A. Theoretical consumption was 0.043 g. The mass over con-

sumption of aluminum electrodes may be due to the chemical

hydrolysis of the cathode. In addition, it can be attributed that

during the electrocoagulation, the cathode is chemically attacked

by OH� ions generated during H2 evolution at high pH [49, 50].

3.9 Kinetic studies

Kinetics studies of treatment process have important role in deter-

mining the hydraulic retention time in any reactor system to achieve

desired removal [31]. So, rate constant is very significant in the

design of wastewater treatment units. It is very essential to know

the type of reaction rates for design a wastewater treatment unit.

Rate of reaction describes the rates of change in concentration of

reactant per unit time. Results showed the removal of dye exhibited

first order kinetic with good correlation coefficients (>0.95) accord-

ing to following equation:

lnC=C0 ¼ �k t (10)

where C0, C, t, and k are the dye concentration before reaction (mg/L),

dye concentration after reaction (mg/L), time of reaction (min), and

reaction rate constant (min�1), respectively.

The values of rate constants at optimum inter electrode distance

and reaction time were presented in Tab. 2. Results show that the

rate constant increases with increasing voltage and electrolyte con-

centration and decreases with increasing dye concentration. Rate

constant of dye removal at monopolar parallel connection was

higher than other connection modes.

Figure 7. Effect of electrode connection mode on dye removal (initial dyeconc.: 50mg/L, 20V, interelectrode distance: 1 cm).

Table 2. Dye removal percentage and rate constants at different conditions

Connection mode Voltage(V)

Dye concentration(mg/L)

Electrolyte concentration(mM)

Dye removal(%)

k(min�1)

Monopolar parallel 5 50 Without NaCl 83.41 0.0598Monopolar parallel 20 50 Without NaCl 98.59 0.142Monopolar parallel 40 50 Without NaCl 99.89 0.227Monopolar parallel 20 75 Without NaCl 96.8 0.1147Monopolar parallel 20 100 Without NaCl 92.5 0.0863Monopolar parallel 20 200 Without NaCl 81.23 0.0557Monopolar parallel 20 300 Without NaCl 69.45 0.0395Monopolar parallel 20 50 With NaCl (0.25mM) 99.45 0.173Monopolar parallel 20 50 With NaCl (0.5mM) 99.95 0.25Monopolar parallel 20 50 With NaCl (1mM) 100 –Monopolar series 20 50 Without NaCl 91.18 0.08Bipolar 20 50 Without NaCl 84.6 0.062



3.10 Dye removal mechanism

Reactive Red198 (RR198) has different groups in its structure. These

groups have three different absorbance peaks at 288, 373, and

518nm. These peaks could be attributed to benzene, naphthalene

rings, and azo linkage, respectively [51]. Dye removal during electro-

chemical processes may be due to destruction of dye molecules to

smaller organic compounds depends on type of electrode material

used. Thus, to evaluate the dye removal mechanism by the electro-

coagulation, the absorbance of raw and treated wastewater at three

absorption wavelengths of 288, 373, and 518nm were measured. In

addition, to determine the presence of aromatic compounds due to

cleavage of dye molecules in the solution, absorbance at 254nm

were measured [51]. Figure 8 shows that all of absorbance peaks

decrease during the electrocoagulation treatment and are almost

completely disappeared after about 30min. These absorbance

peaks reduction indicated that main mechanism for dye removal

was adsorption of dye molecules on flocs. Also it can be concluded

that the removal of RR198 has not been lead to cleavage of azo

linkage to produce other by products. High COD removal of 84.1%

confirms that cleavage azo group has small role in dye removal.

Smaller COD removal compare to dye removal may indicate the low

decomposition of dye molecules to small organic substance via

electro-oxidation.

3.11 Economic analysis

Operation cost during wastewater treatment processes includes

cost of electricity, chemical reagents, cost of sludge disposal,

labors, maintenance, and equipments. In electrochemical process

the most important parameters that affect operating cost are

cost of electrode material and consumed electrical energy. Thus

these items are calculated in this research to determine operating

cost:

Operating cost ¼ a Cenergy þ b Celectrode (11)

where Cenergy, Celectrode, a, and b are energy consumption per cubic

meter of wastewater (kWh/m3), consumed electrode for treatment of

a cubic meter wastewater (kg/m3), average cost of aluminum sheet 3

US$/kg and electricity price 0.0773US$/KWh, respectively.

Operating cost is calculated on basis of prices obtained from

Iranianmarket in Feb 2010. Effect of voltage on electrode and energy

consumption is given in Fig. 9. Results showed that electrode and

energy consumption strongly increased with increasing voltage. In

addition, results showed operating cost for treatment a cubic meter

colored wastewater at optimum operational condition of 20V, inter

electrode distance of 1cm, was 0.256 US$ for 98.59% dye removal at

30min. At high voltage of 40 V at same condition, operating cost

raised to 0.795 US$.

3.12 Efficiency of electrocoagulation to remove

different reactive dyes

Efficiency of electrocoagulation process to remove of three different

reactive dyes (Reactive Black5 (lmax¼ 598nm, molecular mass¼991.82 g/mol), Reactive Blue19 (lmax¼ 592nm), and Reactive

Red198 (lmax¼ 518nm)) was considered (Fig. 10). Results showed

that dye removal percentage in all cases increased with electrocoa-

gulation time. This was in agreement with the results in Section 3.1.

Moreover, dye removal efficiency was followed order: Reactive

Red198, Reactive Black 5, and Reactive Blue19. Required electrocoa-

Figure 8. Absorbance reduction during electrocoagulation of RR198(interelectrode distance: 1 cm, 20V, and dye: 50mg/L).

Figure 9. Effect of voltage on electrode and electrical energy consumptionat optimum condition (interelectrode distance: 1 cm and time: 30min).

Figure 10. Efficiency of electrocoagulation for removal of different reactivedyes (dye: 50mg/L, 20V, interelectrode distance: 1 cm, and pH 5.5).



gulation time to achieve a dye removal efficiency of 98% was 30, 60,

and 60min for Reactive Red198, Reactive Black 5, and Reactive

Blue19, respectively. Also rate constant for 98% dye removal was

0.142, 0.068, and 0.066min�1 for Reactive Red198, Reactive Black 5,

and Reactive Blue19, respectively. The small different in dye removal

efficiency of these dyes may be due to nature of the different func-

tional groups of dyes that change properties of dyes. The above

results indicated that electrocoagulationwas very efficient and clean

process to remove different reactive dyes from synthetic wastewater.

4 Conclusions

The following conclusions are drawn based on the results:

(1) Electrocoagulation is a fast, effective, and clean process to

remove reactive dyes from wastewater.

(2) The treating of colored wastewater using aluminum electrodes

was affected by the voltage, time of reaction, inter electrode

distance, electrode connection mode, initial electrolyte, and

dye concentration.

(3) Dye removal, COD removal, electrode consumption, energy con-

sumption and operating cost, were 98.59%, 84.1%, 0.052kg/m3,

1.303 kWh/m3, and 0.256 US$/m3, respectively (50 ppm RR198,

20V, interelectrode distance of 1 cm and time of 30min).

(4) Dye removal followed first order kinetics.

(5) Monopolar parallel connection mode was the most efficient

connection for dye removal from wastewater.

The authors have declared no conflict of interest.

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