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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 245-251 © IAEME
245
A QUANTITATIVE COMPARISON BETWEEN ELECTRO COAGULATION
AND CHEMICAL DOSING
M.S. Keerthana Rani1
, Dr. D. Elango2
1
Assistant Professor, 2
Head of the Department
Valliammai Engineering College, Kattankulathur
ABSTRACT
Effluents of paint wastewater contain highly toxic compounds and organic biorefractory
compounds such as COD and TOC. It harms fish, wild life, contaminates the food chain if poured
down a storm drain. So paint wastewater must be needed to discharge after treatment. The
characteristics of paint wastewater and efficiency of Electrocoagulation (EC) process by using Al-Al
electrode combination and Chemical coagulation process were studied. In EC study, conductivity
and current density plays a vital role. The effect of operational parameters such as electrolyte
concentration, initial pH and current density was investigated. In chemical coagulation process, the
alum dosage levels were calculated by using faraday’s law. When compare with chemical
coagulation process, the maximum removal efficiency was obtained for EC process by using Al
electrode.
Keywords: EC, Paint Wastewater, Chemical Coagulation, COD Removal Efficiency.
1. INTRODUCTION
Paint is generally considered as a mixture of pigment, binder, solvent, additives. The type and
proportion of each component in the mixture characterize the properties of a particular paint. The
components of paint also determine the characteristics of the waste generated in its manufacture and
use. A convenient method to classify paints is based on their primary solvent for waste reduction and
disposal. In this respect, paints can be classified as water based, organic solvent based or powder
(dry), without solvent.
The term “water based” refers to coating systems that use water as solvent to some extent.
They have advantages over some types of organic solvent based coatings because they generally
decrease Volatile Organic Carbon (VOC) emissions, eliminate organic solvents for thinning and
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING
AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 5, Issue 3, March (2014), pp. 245-251
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2014): 7.9290 (Calculated by GISI)
www.jifactor.com
IJCIET
©IAEME

246
reduce the use of organic solvents for thinning and reduce the use of organic solvents during clean-
up (Korbahti and Tanyolac, 2009). Due to the varying degree of chemicals used, the waste water
contains appreciable concentrations of BOD, Chemical Oxygen Demand (COD), suspended solids,
toxic compounds and color.
The discharge of such colored wastewater into the environment is not only aesthetically
displeasing, but impedes light penetration, damages the quality of the receiving streams and may be
toxic to treatment processes, to food chain organisms and to aquatic life. For these reasons, the
effluent treatment is necessary before their discharge into the environment (Aboulhassan et al.,
2006).
There are many different techniques to remove COD, TOC and color from industrial
wastewater such as biodegradation, adsorption, membrane filtration, coagulation–flocculation,
advanced oxidation processes such as ozone, photochemical, Fenton's, electrochemical etc. These
technologies take considerable time; require an extensive setup and they are not economically
applicable for plants of produced small volume wastewater. These conventional processes generate a
considerable quantity of secondary pollutants which pose serious environmental problems. (Akyol,
2012)
Advantages of the EC compared to conventional chemical coagulation include reduced
wastewater acidification and salinity, low dosage of coagulant, superior coagulant dispersion and
intrinsic electroflotation separation capability.In this study, the feasibility of EC and Chemical
coagulation process for the treatment of paint wastewater in terms of COD was investigated. Effects
of parameters such as electrolyte and its concentration, initial pH, electrode area, inter-electrode
distance, current density and initial concentration of the paint using aluminum electrode were also
studied.
2. MATERIALS AND METHODS
2.1 Chemicals and Materials
The water based paint was obtained from the local car showroom in Trichy. The color of
water based paint used for the treatment was bluish silver (1H7). Sodium chloride and Sodium
sulphate (Merck, 99.9% purity) was utilized as an external electrolyte. Commercially available
aluminum plate (99% purity) was used as an electrode.
2.2 EC process
A set of experimental run were carried out to determine the optimum external electrolyte for
high COD removal. The experimental setup was shown in Fig. 3.3. 800 ml of sample has taken in
the 1 L beaker. It was kept above the magnetic stirrer for continuous agitation. External electrolyte
such as NaCl was added to increase the conductivity. The aluminum rod was used as an electrode.
The size of rod was 5 cm X 7 cm X 0.7 cm. The electrode was immersed into the sample. Initially
electrode area immersed in the sample was 60 cm2
. The spacing between the anode and cathode was
2 cm. then the electrodes were connected with DC supply. The voltage supply has adjusted by DC
supply. The electrolysis process was conducted for 2 hours. The 5 ml of sample were taken for every
10 min. the sample was filtered by using glass filter paper. The pore size of filter paper was 0.45µm.
The sample was analyzed to determine the COD by using COD digester.

247
Fig. 2.1: Experimental setup
2.3 Chemical Coagulation
The coagulation tests were carried out using the jar test. The tests involved rapid mixing,
followed by slow mixing and sedimentation in a batch process. Five beakers were filled with 500 ml
of the real paint wastewater samples, and placed on the floc illuminator and agitated at the
preselected speed of rapid mixing at 120 rpm for 10 min. During the rapid mixing, a known dosage
of alum was added to each beaker simultaneously. After the rapid mixing, the preselected speed of
slow mixing 20 rpm for 20 min was quickly established and when this was completed the beakers
were then carefully removed from the floc illuminator and left for the sedimentation phase. After
settling, 5 ml of the sample was taken from the middle of each beaker for COD analysis.
3. RESULTS AND DISCUSSIONS
3.1 Study of EC process in paint wastewater by using Al electrode
The experiment was carried out in raw wastewater. The COD removal efficiency was 50 % at
the electrolysis time of 45 mins. The conductivity of the sample was around 189 µS. The external
electrolyte as NaCl was added to increase the conductivity. When the conductivity increases, current
produced also increased.
3.1.1 Determination of NaCl concentration
The initial COD concentration of paint wastewater was 1000 mg/L. The experimental
conditions maintained were spacing 2 cm, area of electrode dipped in sample 60 cm2
, voltage
supplied 10V. The results obtained by adding the external electrolyte NaCl in different concentration
were shown in Fig. 3.1. The concentration of NaCl electrolyte was varying like 200 mg/L, 300 mg/L,
and 400 mg/L. It explains that, by increasing the electrolyte concentration, the COD removal also
increased. The maximum COD removal of 57.12 % was achieved with 400 mg/L concentration in 10
min. The addition of NaCl contributes chloride ions to the solution. It removes the insulating layer
formed by Ca2+
and Mg2+
on electrode (Raghavacharya, 1997; Wong. H. M., 2002).
1 - Reactor, 2 – Cathode, 3 – Anode, 4 - AC to DC convertor,
5 -magnetic stirrer bar, 6 - Magnetic stirrer

248
Fig. 3.1: Variation in removal efficiency with varying NaCl dosage
3.1.2 Determination of Optimum pH
The initial condition to carried out the process were the initial COD concentration of sample
1000 mg/L, NaCl concentration 300 mg/L, area of electrode immersed in sample 60 cm2
, spacing
between the electrodes 2 cm, voltage applied 10 V. The Fig. 3.2 shows the COD removal for various
pH. The pH was varying like 5, 6, 7, 8 and 9. For pH 6, 76 % of maximum removal efficiency was
observed at 10 min. At pH 5, Al3+
is transformed into soluble monomeric species such as Al(OH)2
+
,
Al(OH) 2+
and Al(OH)2 (Bensadok et al., 2008). So the optimum pH for the process is considered
as 6.
Fig. 3.2: Variation of removal efficiency with varying pH
3.1.3 Determination of Optimum Current Density
The condition maintained for the process were the initial COD concentration of sample 1000
mg/L, NaCl concentration 300 mg/L, pH 6 area of electrode immersed in sample 60 cm2
and
spacing of electrode 2 cm. Fig. 3.3 shows the variation in COD removal when changing the voltage
supplied for electrolysis process. The voltage was varying like 6 V, 8 V, 10 V and 12 V. The amount

249
of current density determines the coagulant dosage and size of the bubble production. It affects the
growth of flocs (Adoum et al., 2004). An increase in removal efficiency of 73% from 31.3% was
observed when the current density was increased from 1.333 mA / cm2
(6 V) to 3.667 mA / cm2
(12
V) at 10 min. So 12 V is considered as the optimum voltage for this study.
Fig. 3.3: Variation of removal efficiency with various voltage supply
3.1.4 Determination of Effect of Initial Concentration of Paint Wastewater
The condition maintained for the process were the NaCl concentration 300 mg/L, pH 6, area
of electrode immersed in sample 60 cm2
and spacing of electrode 2 cm, voltage supplied 12 V. The
Fig. 3.4 shows the variation in COD removal when changing the initial COD concentration of paint
wastewater. The initial COD concentration of paint wastewater was varying like 1000 mg/L, 2000
mg/L, 3000 mg/L and 5000 mg/L Removal efficiency decreased when increasing the initial
concentration. The maximum COD removal efficiency for 1000 mg/L was 73 % in 10 min. In high
concentrations, insufficient hydroxyl and metal ions production on the electrodes are the reason for
less removal efficiency (Sengil and Ozacar, 2009).
Fig. 3.4: Variation of removal efficiency with various initial concentrations

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3.2 Chemical Coagulation
The removal efficiency of paint wastewater without supplying current was studied by using
chemical coagulation process. To compare the results with Al electrode alum was used as a chemical
coagulant. The alum concentration was calculated by using Faraday’s law. For maximum removal, the
optimum conditions like alum dosage concentration and initial pH were studied. The results obtained
were given below.
3.2.1Determination of Alum Dosage
The initial COD concentration of the sample was 1000 mg/L and pH was 7. To analyze the
effect of alum dosage, the dosage concentration was varying like 0.6 g/L, 1.2 g/L, 1.8 g/L, 2.4 g/L and
3 g/L respectively. The variation of COD removal for different alum dosage is shown in Fig.3.5. The
COD removal efficiency was increased by increasing the alum dosage. The maximum COD removal
efficiency of 66 % was observed for the dosage concentration of 3 g/L. The dosage concentration of 3
g/L was considered as optimum dosage.
Fig. 3.5: Variation of removal efficiency for various alum dosages
3.3 Comparison of EC and Chemical Coagulation
Fig. 4.31 shows the comparison of COD removal efficiency by chemical coagulation and EC
by Al electrodes. The maximum removal efficiency achieved by EC process using Al electrode was
73 %. When compare with chemical coagulation process, electrocoaguation process giving the
maximum removal efficiency. So EC process using Al electrode was considered as the most
preferable method for treatment of water based paint wastewater.
4. CONCLUSION
The fundamental physical separation processes are different for chemical dosing and EC,
with settling being the key removal path in the former case. In EC, however, the dominant removal
path is determined by the applied current. At low currents, settling dominates. As the current
increases, so the pollutant fraction that is removed by flotation increases, although the coagulant
appears to be used less effectively. Experimental data support the hypothesis that the increased
bubble densities associated with higher currents are removing flocs of coagulant from solution. The
mechanism of coagulant delivery is a key difference between chemical dosing and EC performance.
In the alum dosing studied here, coagulant addition is a discrete event with the system. By comparing

251
the EC and chemical coagulation process results, helps to conclude that EC process giving the
maximum removal efficiency. So EC process is considered as the suitable process for treatment of
water based paint wastewater.
REFERENCES
1. Abdurrahman Akyol, (2012), treatment of paint manufacturing wastewater by
electrocoagulation, Desalination, 285, 91-99.
2. Aboulhassan. M. A., S. Souabi, A. Yaacoubi , M. Baudu, (2006), Improvement of paint
effluents coagulation using natural and synthetic coagulant aids, Journal of hazardous
materials, B138, 40-45.
3. Adhoum. N, Lotfi Monser, Nizar Bellakhal, Jamel-Eddine Belgaied (2004), Treatment of
electroplating wastewater containing Cu2+
, Zn2+
and Cr(VI) by electrocoagulation, Journal of
Hazardous Materials, B112,207–213.
4. Bahadir K.Korbahti, Abdurrahman Tanyolac, (2009), Electro chemical treatment of
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5. Bensadok. K , S. Benammar, F. Lapicque, G. Nezzal, (2008), Electrocoagulation of cutting
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6. Raghavacharya. C, (1997), Colour removal from industrial effluents-a comparative review of
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8. Wong. H. M., C. Shang, Y.K. Cheung and G. Chen, (2002), Chloride Assisted
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Protection Conference, Tsin Chu, Taiwan.
9. J.M. Sieliechi, R. Kamga and G. Joseph Kayem, (2013), “Coagulation-Settling of Natural
Organic Matter from Soft Tropical Water using Aluminium and Iron(Iii) Sulphate”,
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10. C. P. Pise, Dr. S. A. Halkude, (2012), “Blend of Natural and Chemical Coagulant for
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