Electrocoagulation: operational parameters, sludge & economic analysis

The performance of electrocoagulation (EC) was studied by conducting experiments for the removal of Reactive Orange 4 dye from its synthetic aqueous solution. The effect of operational parameters (initial solution pH, current density, inter-electrode distance, electrolysis time and retention time, solution temperature, conductivity and different electrode combinations) on the efficiency of EC was studied and the results were analysed in terms of colour removal efficiency (CRE), electrical energy consumption (EEC) and operating cost (OC). The effect of different anions on the efficiency of EC was studied by conducting experiments with electrolytes containing chloride, sulphate, carbonate and nitrate ions. The characterisation of EC generated sludge was performed using XRD. A maximum CRE of 95% was obtained for EEC of 1.7 kWh/m3 and OC of 0.45 US $/m3. It was found that the addition of electrolyte containing chloride ions resulted in higher CRE (93–95%) compared to electrolytes containing sulphate and carbonate ions as their presence can lead to passivation of the electrode surface & thereby resulting in a reduction in CRE (60% and 41%, respectively). The addition of sodium chloride as an electrolyte resulted in minimum EEC and OC. The Al/Al electrode combination provided the maximum CRE and least EEC & OC. The increase in solution temperature leads to reduction in CRE and CE due to formation of passive layer on the surface of electrodes. However, a reduction in cell potential and EEC was noticed with an increase in solution temperature.