CHAPTER 2
LITERATURE REVIEW
2.1 General
Electrocoagulation is a technology for the treatment of polluted water using electricity. Electrocoagulation process is effective in treating soluble or colloidal pollutants in various effluents including municipal, laundry, food industry, tanneries, textile, and agro-based industry wastewaters. Electrocoagulation process includes coagulation and precipitation of contaminants by applying direct current. It consists of an electrolytic cell and electrodes. A direct current is applied to the electrodes to induce the reaction needed to achieve the coagulation.
In recent years, smaller scale electrocoagulation processes have advanced to the point where they are seen as a reliable and effective technology. A wide range of reactors has been tried, with individual designs being largely determined by the volumetric scale and nature of the pollutant being treated. This diversity in reactors has resulted in isolated advances being made in electrocoagulation technology. (Naje and Abbas, 2013, Malaysia).
2.2 Theory of Electrocoagulation
The basic principle of electrocoagulation process depends on the cations produced electrolytically from anode and coagulation of contaminants are increased in the aqueous solution. Electrophoretic motion tends to concentrate negatively charged particle in the region of the anode and positively charged particles in the region of the cathode. The consumable metal anodes are used to continuously produce polyvalent metal cations in the region of the anode. These cations neutralize the negative charge of the particles and move towards the anodes by production of polyvalent cations from the oxidation of the sacrificial anode and the electrolysis gases like hydrogen evolved at the anode and oxygen evolved at the cathode.
The three successive stages of electrocoagulation process involve:
‘ Electrolytic oxidation of the sacrificial electrode for the formation of coagulants.
‘ Suspension of contaminant particulate and emulsion breakage are due to the destabilization.
‘ Flocs formation due to the aggregation of the destabilizes phase
The mechanism involved in destabilization of contaminants and particulate suspension are as follows:
i. Generation and interaction of ions are possible due to the oxidayion of the sacrificial anode. Compression of the diffuse double layer is seen possible around the charged ions.
ii. Counter ions are produced from the electrochemical dissolution of the sacrificial anode. Neutralization of ionic species in the wastewater is because of these counter ions. The reduction of the electrostatic interparticle repulsion is due to these counter ions, Vander Walls attraction predominates and coagulation occurs and approaches zero net charge.
iii. In the aqueous medium, coagulation causes formation of flocs and also creates a blanket of sludge.
iv. Adsorption of contaminated contents is due to the negative surfaces of the hydroxides, oxyhydroxides and solid oxides.
v. Metal ions are generated due to the dissolution of the elelctrodes from the anode. Polymeric ions or metal hydroxides are hydrolyzed immediately after the generation of metal ions.
The main function of sacrificial anode is to generate polymeric hydroxides nearby the anode. These polymeric hydroxides are act as excellent coagulating agents. Due to electrophoresis action, negative ions which are produced from the cathode moves towards anode Small bubble of oxygen at anode and small bubbles of hydrogen at cathode are generated and are responsible for electrolysis of water. These bubbles attract the flocculated particles. Due to the natural buoyancy towards the surface the flocculated particle floats.
The physicochemical reactions that occur in the electrocoagulation cell is described as follows:
i. Metal ions reduction takes place at the cathode.
ii. Impurities are responsible for cathodic reduction in the wastewater.
iii. Due to the electrode erosion, colloidal particles are generated.
iv. Coagulation and discharge of colloidal particles are because of electroflotation or sedimentation and filtration.
v. Electrophoresis in the solution causes ions migration.
vi. At anode and cathode oxygen and hydrogen bubbles are produced.
vii. Other chemical and electrochemical process also occurs and an external power supply is used for the electrocoagulation process.
Deposition and dissolution of metal ions at the electrodes are due to the quantity of electricity that has been passed. A relationship between current density (Acm-2) and the quantity of the metal (M) dissolved (g of Mcm-2) can be found out by using Faraday’s law.
Where, W is the electrode dissolution (g of Mcm-2), I is the current density (Acm-2), t is the time in second, M is the electrode’s relative molar mass, n is the no. of electrodes, F is the Faraday’s constant, 96,500 Cmol-1.
The operating condition of electrocoagulation mainly depends on the chemistry of the aqueous medium, conductivity and pH. Particle size, electrode material, electrode distance and chemical constituent concentration are other important characteristics. Electrophoresis motion tends to concentrate positively charged ions in the regions of the cathode and negatively charged particles in the region of the anode. Polyvalent metal cations are continuously produced in the vicinity of the anode. The negative charge of the particle is neutralized by the produced cations by the motion of electrophoresis.
2.3 Reaction mechanism in Electrocoagulation process
The processes and reactions that occur during electrocoagulation are explained as follows. When current is passed through electrochemical reactor, it just overcomes the equilibrium potential difference, anode over potential, cathode over potential and potential drop of the solution. The anode over potential includes the activation over potential and concentration potential, as well as the possible passive over potential resulted from the passive film at the anode surface, while the cathode over potential is principally composed of the activation over potential and concentration over potential. Reaction occurs at electrode surfaces and forms coagulants in aqueous phase, adsorption of soluble or colloidal pollutants occurs on coagulants. The chemical reactions generally taking place at the anode and cathode are given as follows:
At the anode:
M (s) M (aq)
n+ + ne-
2H2O 4H+ + O2 + 4e-
At the cathode:
M (aq)
n+ + ne- M (s)
2H2O + 2e- H2 (g) + 2OH-
M represents the material used as electrode and n is the number of electrodes.
Generally, aluminum and iron electrodes are used as electrode materials in the electrocoagulation process. In the iron electrode, following two mechanisms are expected to occur.
Mechanism 1:
Anode:
4Fe(s) 4Fe2+ (aq) + 8e-
4Fe2+ (aq) + 10H2O (I) + O2 (g) 4Fe (OH)3 (s) + 8H+ (aq)
Cathode:
8H+ (aq) + 8e- 4H2 (g)
Overall: 4Fe(s) + 10H2O (I) + O2 (g) 4Fe (OH)3 (s) + 4H2 (g)
Mechanism 2:
Anode: Fe (s) Fe2+ (aq) + 2e-
Fe2+ (aq) + 2OH- (aq) Fe (OH)2 (s)
Cathode:
2H2O (I) +2e- H2 (g) + 2OH- (aq)
Overall: Fe (s) + 2H2O (I) Fe (OH)2 (s) + H2 (g)
Due to oxidation in an electrolyte system, iron produces form of monomeric ions. Fe(OH)3 and polymeric hydroxyl complex such as: Fe(H2O)63+ , Fe(H2O)52+, Fe(H2O)4(OH)2+, Fe(H2O)8(OH)24+ and Fe(H2O)6(OH)44+ depending upon the pH of the aqueous medium.
In the case of aluminum electrodes, reactions are as follows:
Anode: Al (s) Al3+ (aq) + 3e-
Cathode: 3H2O (I) + 3e- 3/2 H2 + 3H+
For the aluminum electrodes, Al3+ (aq) ions will immediately undergo further spontaneous reaction to generate corresponding hydroxides and polyhydroxides. Due to hydrolysis of Al3+: Al (H2O)63+, Al(H2O)5OH2+, Al(H2O)5OH2+, Al(H2O)OH2+ are generated. This hydrolysis products produced may be monomeric and polymeric substance such as, Al(OH)2+, Al2(OH)24+, Al6(OH)153+, Al7 (OH)174+, Al8(OH)204+, Al13O4(OH)247+, Al13(OH)345+ (Chaturvedi, 2013, India).
2.4 Factors influencing electrochemical coagulation
The removal efficiency of the pollutants from wastewater is affected by the various parameters. The parameters influencing the process of electrocoagulation are:
‘ Electrode material: The material of the electrodes can be iron, aluminum or inert material (cathode). Optimal material selection depends on the pollutants to be removed and the chemical properties of the electrolyte. Aluminum seems to be superior compared to iron in most cases, when only the efficiency of the treatment is considered. However, it should be noted that aluminum is more expensive compared to iron. Inert electrodes, such as metal oxides coated titanium, are used in some cases. When water has significant amounts of calcium and magnesium ions, the inert cathode materials can be used. For COD and phenol removal, iron is good and for color and turbidity removal aluminum gives better results. If electrochemically inert materials like stainless steel as cathode are used, gets protection from corrosion. Besides, stainless steel produces smaller bubbles which posses larger surface and can remove more impurities through floatation.
‘ pH: pH of the wastewater has an effect on the speciation of metal hydroxides in the solution. During electrocoagulation pH increases due to the contribution of OH- ions into the solution and it enhances the efficiency of the system. Initial pH between 7-9 gives better results and if pH raises beyond 9 the efficiency decreases because of the formation of soluble Fe(OH)4 and Al(OH)4. Only insoluble metal hydroxides of iron can remove pollutants by electrostatic attraction. The kinetics of conversion of Fe2+ to Fe3+ is strongly affected by bulk solution pH.
‘ Current density: Current density is proportional to the amount of electrochemical reactions taking place on the electrode surface. When current density increases, the reaction rate also increases by the more metal ions in solution. But the rapid contribution of metal ions in the system cost more and further increases the results in restabilization of metal particles in the solution.
‘ Electrolysis time: Treatment time added per volume is proportional to the amount of coagulants produced in the electrocoagulation system and other reactions taking place in the system. Efficiency increases with increase in electrolysis time. But if we increase the electrolysis time beyond some extend the removal efficiency decreases because of the free metal ions in the solution.
‘ Temperature: Temperature affects floc formation, reaction rates and conductivity. Depending on the pollutants, the increasing temperature can have a negative or a positive effect on the removal efficiency. Normally, better results are obtained at low temperature, while at higher temperature results in dissolution of metal ions into the solution.
‘ Inter electrode distance: The distance between the electrodes has greater importance in elctrocoagulation. Very less electrode distance may cause short circuit and very high distance results in lesser contribution of metal ions into the solution which minimizes the efficiency of the system. So it is better to keep this in medium according to the characteristics of the wastewater (Shreesadh et al, 2014).
2.5 Investigation of ECC for domestic wastewater and greywater
Barisci and Turkay, 2016, Turkey conducted experiments on ‘Domestic greywater treatment by electrocoagulation using hybrid electrode combinations’. Electrochemical coagulation experiments were carried out with different electrode combination for the treatment of domestic greywater. The different electrode combinations were Al-Al-Al-Al, Fe-Fe-Fe-Fe, Fe-Al-Al-Fe, Al-Fe-Fe-Al, Fe-Al-Fe-Al, Al-Fe-Al-Fe, Fe-Al-Al-Al, Al-Fe-Fe-Fe. The operating parameters they considered were current density, initial pH and supporting electrolyte concentration. They have conducted the experiments for the current densities 0.5, 1.0 and 1.5 mA cm-2. The supporting electrolyte they have used is sodium sulfate. They have also carried out experiments to see the effect of initial pH in all the range i.e., original pH (7.62), acidic (3) and basic (9.5). The electrolyte concentrations were 0, 50 and 100 mgL-1. The maximum COD removal efficiency was 98% at the current density of 1.5 mA cm-2 while using Al-Fe-Fe-Al electrode combination.
Hussien et al, 2015, Egypt carried out ‘Sewage water treatment via electrocoagulation using iron anode’. The operating parameters considered in this research were current density, electrolysis time, electrolyte concentration, electrode distance. The reactor used was of 1.25 liter capacity. Iron electrodes of 2 x 2 cm were used. Different grade emery washed with distilled water was used to polish the electrodes mechanically and rinsed with acetone, and dried in a stream of air. The electrode distance was 3 cm. One liter sewage used in each experiment. Digital multimeter was used to measure both voltage and current. The Sodium chloride was used as supporting electrolyte. The electrocoagulation experiments were carried out at ambient temperature 250C. Supporting electrolyte was added in the desired amount to raise the conductivity of the solution and then the pH adjusted to the desired value. The sludge was separated by filtration with Whatman filter paper. Then supernatant was analyzed, and the weight of the dissolved iron was calculated from the change in weights of the electrode before and after electrocoagulation. The anodic dissolution percentage was calculated from the equation,
, where, ECE is the electrochemical equivalent of iron. The effective removal of S.S, COD, and BOD were obtained under the optimum operating parameters: pH 7.6, 65 mA cm-2 of current density was applied, ET 30 min, and sodium chloride as supporting electrolyte concentration of 1gL-1 and electrode gap distance of 3 cm. The suspended solids, COD, and BOD decreased from 507, 670, and 446 to 5, 98, and 77mgL-1 respectively.
‘Domestic Wastewater Treatment by Electrocoagulation using copper and aluminum electrodes’ was carried out by Impa et al, 2015, India. Borosil glass beaker of 5 liter capacity was used as reactor to hold the sample. Aluminum and copper electrodes of dimension 150”50”3 mm were used. Electrode spacing was 3 cm. The cell was equipped with the magnetic stirrer. The efficiency was studied for different voltages and electrolysis time. For every 10, 20, 30 min the sample were drawn from the reactor and parameter like COD and nitrates was measured. Before every run the electrodes were washed with 15% HCl and then rinsed with distilled water. After the experiment, the sample is transferred to another beaker and kept undisturbed for 20 min to allow the flocs formed to settle. Under the operating parameters such as electrolysis time: 30 min, pH: 7-8 and voltage: 20V, the 63.2% and 62% of COD and nitrate removal was obtained respectively. After conducting the experiments, they have concluded that the applied potential increases the rate of dissolution of electrodes. They have also stated that COD and nitrate removal efficiency is directly proportional to the input voltage and contact duration. Finally the results of study showed that the electrochemical coagulation could be applied for the cost effective treatment of domestic wastewater.
Santhosh et al, 2015, India worked on ‘Treatment of sullage wastewater by electrocoagulation using stainless steel electrodes’. This study was carried out for the treatment of sullage wastewater using electroagulation with stainless steel electrodes as sacrificial anode in bipolar arrangement. pH, cell voltage and electrolysis time were the operating parameters they have considered. The experiments were carried out in a batch reactor of 500 mL beaker. Electrode used was stainless steel with dimensions 70 x 50 x 3 mm. The electrode distance was maintained at 40 mm. The experiments were carried out at different voltages such as 4, 6 and 8V. Before every experiment the electrodes were washed with 1M H2SO4 and then rinsed with deionised water. After the experiment, the treated sample is kept undisturbed for 20 min to allow the flocs to settle, and then the supernatant was analyzed for suspended solids, COD and BOD. 92.71%, 88.76% and 93.1% reduction of COD, BOD and SS was obtained at 8V, 30min respectively.
Kanawade, 2015, India worked on ‘The Wastewater Treatment and its Reuse’. The circular cell having 20cm internal diameter and 50cm height with the effective volume of 5L and two iron electrodes of 32cm2 surface area was used for experiments. The distance between the electrodes was 3cm. The temperature was maintained between 25-300C. The agitation speed was 100rpm. The operating parameters were electrolysis time, electrode spacing and applied current. To examine the influence of current density, 0.03, 0.2, 0.4, 0.79 and 1.0A current was applied for the electrolysis time of 30min, with the corresponding current densities of 0.94, 6.25, 12.5, 24.7 and 31.25 mA cm-2 respectively. The maximum removal of turbidity, COD and TSS was 91.8%, 77.2% and 68.5% at of 24.7 mA cm-2 current density with an inter-electrode distance of 5cm within the electrolysis time of 30min.
Alex and Paul, 2015, India worked on ‘Municipal Wastewater Treatment by Electrocoagulation’. The process of electrocoagulation was examined with the laboratory setup with aluminum anode and stainless steel cathode for the removal of COD and TS. The electrolytic cell reactor was made up of acrylic sheet with internal dimensions of 12.5x 8x 9 (L x B x H) cm. The wetted surface area of the electrodes was 90cm2. For each run 500mL sample was taken. After each run 1min of rapid mixing and 4min of slow mixing was done using magnetic stirrer for getting completely settled sludge. 90min of settling time was allowed after each run. The operating parameters were cell voltage, electrode distance and electrolysis time. The different applied cell voltages were 8, 10, 12, 14 and 16V. The inter electrode distance was varied from 1-4 cm. The electrolysis time was from 10-30 min. The maximum removal of COD and TS was obtained at 10V with 2cm electrode spacing at 25min. At the optimal conditions, the Cod got reduced from 332mgL-1 to 64mgL-1 and TS got reduced from 984mgL-1 to 380mgL-1. Therefore, the removal efficiency of COD and TS were 80.70% and 61.38% respectively. It was inferred that with the increase in cell voltage and electrolysis time, the removal efficiency increases. Also, smaller electrode distance produces more anions which increase the treatment efficiency.
In 2014, Kruna and Pandya, India, carried out ‘Electrocoagulation – A Promising Technology for Sewage Treatment’. The batch reactor of dimension 380 x 235 x 255mm was used for the experiment. Electrodes (4 Aluminum as cathode and 3 Mild Steel as anode) were used. The electrode spacing was 10 and 15mm. 10A and 24V are fixed in power supply unit. Sampling was done at time interval of 15min, 20min, 25min, and 30min. After the experiment, the sample is kept undisturbed for 60min in order to allow the flocs to settle. After settling, the supernatant is collected and analyzed for suspended solids, COD and TDS. The operating parameters were electrolysis time, electrode distance, and current density. Suspended solids, COD and TDS removal efficiency was 95%, 86% and 70% respectively at 42 Am-2 current density, 10mm electrode distance in 30min at the optimum pH of 8.3.
Dayananda et al, 2014, India carried out the experiment for ‘Domestic wastewater using Fe-Al electrodes’. The glass reactor of 1.3L capacity of dimension 250”70”100 mm was used and sample volume was maintained 1L for every experiment. Iron electrodes were used as anode while aluminum as cathode. The dimension of the electrodes was 90”40”2 mm. The spacing between the electrodes was 50mm. Different set of experiments was conducted used 2 electrodes and 4 electrodes for various voltages such as 5, 10, 15V for electrolysis time of 30min. While using 2 electrodes the removal efficiency of phosphate, nitrate and COD was less than 30% for 15V at 30min but BOD removal efficiency was 80%. Phosphate, nitrate, COD and BOD removal efficiency was 92.98%, 95%, 90% and 95% with 4 electrodes at 30min for 15V.
Nguyen et al, 2014, Korea worked on ‘Enhanced phosphorus and COD removals for retrofit of existing sewage treatment by electrocoagulation process with cylindrical aluminum electrodes’. A series of experiments were conducted to investigate the retrofit ability of removing total phosphorus and COD from wastewater using cylindrical aluminum electrodes in batch and continuous operating modes. The operating parameters were pH, electrolyte concentration, HRT, initial phosphorus concentration and temperature. The applied cell voltages were 3, 4 and 5V with the current densities 7.04 to 16.08 Am-2 in batch mode and from 7.48 to 21.69 Am-2 in continuous mode. The electrolyte used was NaCl. The electrolysis time in the limits of 1- 20min were tired for different wastewater including synthetic wastewater and municipal wastewater. The maximum removal efficiency of TP and COD is 99% and 75% for the above operating conditions.
‘Optimization of electrocoagulation process to treat grey wastewater in batch mode using response surface methodology’ was studied by Karichappan et al, 2014, India. To treat the greywater, the electrocoagulation process was carried out under the different operating conditions such as initial pH, current density, electrode distance and electrolysis time by using stainless steel electrodes. Electrolytic cell was made up of acrylic material of 3L volume but 1.6L of wastewater was used for the all the experiments. The dimensions of the electrodes were 33cm x 6mm. The distance between the electrodes was varied from 4-6cm. The active surface area of the electrodes was 108cm2. The agitation speed was kept constant at 250rpm. NaCl and HCl were used as the supporting electrolyte. After the treatment, wastewater was centrifuged at 6500rpm for 15min and the supernatant was analyzed for TS, COD and FC. Box-Behnken response surface experimental design (BBD) with four factors at five levels was used to optimize and investigate the influence of process variables such as initial pH (4’8), current density (10-30 mA cm-2), electrode distance (4-6 cm) and electrolysis time (5’25 min) on the TS, COD and FC removal. The optimal conditions were found to be: initial pH of 7, current density of 20 mA cm-2, electrode distance of 5cm and electrolysis time of 20min. Under these optimal operating conditions, the experimental removal efficiencies (98.45, 94.75 and 96.34%) were closely agreed with the predicted values (99.87, 95.47 and 97.15%).
Sharma and Chopra, 2013, India worked on ‘Removal of COD and BOD from biologically treated municipal wastewater by electrochemical treatment’. Here, they investigated the effect of current density (CD), operating time (OT), inter electrode distance (IED), electrode area (EA), initial pH and settling time (ST) using Fe-Fe electrode combination on the removal of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) from biologically treated municipal wastewater (BTMW) of Sewage Treatment Plant (STP). The maximum removal of COD (92.35%) from BTMW was found with the optimum operating conditions of CD (2.82 Am-2), OT (40 min), IED (0.5 cm), EA (160 cm2), initial pH (7.5) and ST (60min), while the maximum removal of BOD (84.88%) was found with the ST (30 min) at the same operating conditions. There was no need of pH adjustment of the BTMW during ET as the optimal removal efficiency was close to the pH of 7.5. Under optimal operating conditions, the operating cost was found to be 54.29 Rs.m-3 / 1.08 US$ m-3 in terms of the electrode consumption (78.48 x 10-5 kg Al m-3) and energy consumption (108.48 Kwh m-3).
Iswanto et al, 2013, Indonesia conducted the experiments for ‘Domestic Waste Water Treatment by Electrocoagulation’. In this study, the wastewater treatment reactor consists of electrocoagulation and flocculation unit. The dimension of the electrocoagulation unit was 20cm length, 10cm width, 15cm height. Aluminum plates were used as anode and iron plates as cathode. Each plate has a dimension of 10x10x14cm. The distance between each plate was 0.5cm. The total number of plates used was 34. Flocculation unit have the capacity of 480L with rapid stirring of 150rpm and slow stirring of 60rpm during 20min. Wastewater was collected from settlement and restaurant area. Retention time for each treatment consisted of 5s to discharge 24 L min-1, 10s to discharge 12 Lmin-1 and 20s at the rate 6 Lmin-1. The parameters considered in this study were TSS, COD, BOD5 and NO3. For the settlement wastewater with the retention time of 20s, the removal efficiency of TSS (80.50%), COD (82.10%), BOD5 (85.72%) and NO3 (57.06%) was observed. For the restaurant wastewater, the removal efficiency of TSS (77.26%), COD (55.93%), BOD5 (58.10%) and NO3 (59.70%) was achieved.
In 2012, Sarala, India reported ‘Domestic Wastewater Treatment by Electrocoagulation with Fe-Fe Electrodes’. The electrolytic cell was of 1.2L capacity. In this experiment iron electrodes are used and the sampling is made at the different interval of time i.e., 5, 10, 15 and 20min. Experiments were conducted at different current 0.12, 0.25, 0.36A.The combination effects of current, pH and time to the efficiency of the electrocoagulation process for the removal of COD, TDS, pH, color, chlorides etc. from the domestic wastewater showed that only current and time have correlation with each other. In this process, sludge formed after the electrocoagulation process was removed by filtration. COD was reduced to 90% with increase of contact time for different current. Maximum COD reduction of COD was observed at 20min for 0.25A and 0.36A. It was observed that the experiment conducted at 0.25A for 20min has maximum removal efficiency of COD, TDS, chlorides and suspended solids of 76.9%, 91%, 38.3% and 87.5% respectively.
Yadav et al, 2012, India conducted ‘Removal of various pollutants from wastewater by electrocoagulation using iron and aluminum electrode’. This study dealt with removal of various pollutants from the industrial wastewater by electrocoagulation treatment. Wastewater was collected and treated by electrocoagulation process using iron and aluminum electrodes. The removal of Cr, Zn, Ni and Cu were achieved up to 100, 98.71, 69.22 and 48.08% respectively using aluminum electrode while Cr, Cu, Zn and Ni were removed up to 100, 78.57, 75.48 and 58.68% respectively using iron electrode electrocoagulation. COD, TDS and sulfate were removed up to 83.94%, 46.92%, 74.16% and 83.66%, respectively in aluminum electrode electrocoagulation while the same were removed up to 54.83, 77.39, 52.85 and 60.74% respectively in iron electrode electrocoagulation.
‘Treatment of laundry wastewater by electrocoagulation’ was studied by Janpoor et al, 2011, Iran. Using an undivided plastic electrocoagulation cell of dimension (20cm”10cm”15cm) and aluminum sheets of dimension 20×7.5×2 mm was used as electrodes. The operating parameters were pH, voltage, HRT and number of electrodes. The electrodes spacing was varied 15 and 30 mm. Magnetic stirring of speed 400 rpm was applied for homogenous mixing of the sample. A DC stabilized power source was used to supply constant current (0’2 A) at variable voltage 10, 20 and 30V. The maximum removal efficiency of COD and phosphorus was 89.9% and 90.0 % at 30V, 90min and 1.5cm electrode spacing.
Wang et al, 2009, Taiwan worked on ‘Removal of COD from laundry wastewater by electrocoagulation/electroflotation’. The electrocoagulation unit consists of the electrochemical reactor of 1 dm3 with 3 Al anodes and 3 Al cathodes. The dimension the electrodes was 40mmx30mm. The total surface area of the cathode and anode was 72cm2. The electrode distance was maintained 10mm. The agitation speed was 200rpm. The operating parameters were cell voltage and initial pH. The initial pH of the wastewater was 7.5. To investigate the effect of initial pH for the removal of COD, the pH of the wastewater was adjusted to the desired value, ranging from 2.5-9.5. The COD removal of 66% was observed when the pH of the wastewater is 5.1. To examine the effect of cell voltage on the removal of COD, the experiments were carried out with the different voltages: 1, 3, 5 and 7V. The maximum COD removal was 65% for 7V for 40min ET.
Bukhari, 2008, Saudi Arabia, conducted experiments on ‘Investigation of the electrocoagulation treatment process for the removal of total suspended solids and turbidity from municipal wastewater’. In this study, wastewater samples of 1.2L was collected in an electrochemical cell with the stainless steel electrodes dipped into the sample solution up to an active surface area of 88cm2. The operating parameters were current density and contact time. The different applied currents were 0.05, 0.1, 0.2, 0.4 and 0.8A. The maximum TSS and BOD removal efficiency of 95.4% and 99% respectively was observed at the current of 0.8A at the ET of 5min.
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