Treatment of tannery liming drum wastewater by electrocoagulation.

The removal of COD, suphide and oil-grease from tannery liming drum wastewater was experimentally investigated using direct current (DC) electrocoagulation (EC). In the EC of the wastewater, the effects of initial pH, electrolysis time and current density were examined. The COD, sulphide and oil-grease in the aqueous phase were effectively removed when mild steel electrodes were used as sacrificial anode. The optimum operating range for each operating variable was experimentally determined. The experimental results show that COD, sulphide and oil-grease was removed effectively. The overall COD, sulphide and oil-grease removal efficiencies reached 82%, 90% and 96%, respectively. The optimum current density for removal of COD, sulphide and oil-grease in the tannery liming drum wastewater were 35 mA/cm(2), 35 mA/cm(2) and 3.5 mA/cm(2) at 10 min electrolysis time and pH 3, respectively. Mean energy consumptions were 5.768 kWh/m(3) of COD, 0.524 kWh/m(3) of sulphide and 0.00015 kWh/m(3) of oil-grease. Results show that the pseudo-second-order rate equation provides the best correlation for the removal rate of the parameters.