Electrocoagulation and Electrooxidation of Automobile Industry Wastewater

Abstract

Electrocoagulation and electrooxidation processes with aluminium and steel electrodes respectively have been used to improve the physicochemical properties of wastewater from an automobile industry. The physicochemical analyses of the wastewater done by American public health association (APHA)/ American Water Works Association (AWWA)/ Water Environment Federation (WEF) recommended standard methods showed that chromium (0.714mg/l), lead (2.44mg/l) and turbidity (120 NTU) did not meet the requirements for discharge by FEPA (Federal Environmental Protection Agency of Nigeria) and cadmium was marginally met. The optimum time for electrocoagulation, 50mins, was determined by measuring the conductivity of wastewater over a 90-minute period. Since the cost of electrocoagulation depends on the current density, the effect of current density on the concentration of pollutants (metals), COD (Chemical oxygen demand) and BOD5 (Five-day Biochemical oxygen demand) has been verified. On the average, the current density of 25.86mA/cm2 was effective in substantially reducing the concentration of lead by 96.36% (0.089mg/l), chromium by 88.66% (0.081mg/l) thereby making the wastewater meet the FEPA standard for discharge, which are 0.12mg/l and 0.1mg/l respectively. At this current density, cadmium concentration was reduced by 87.64% (0.011mg/l) which clearly met the limit of discharge of 0.1mg/l, but the turbidity which reduced by 87.50% (15NTU) did not meet the requirement of 10NTU for discharge. Though the COD and BOD5of the wastewater were within acceptable limits, electrooxidation of the wastewater at the optimal time of 80 minutes with an average current density of 18.85mA/cm2 reduced the COD by 73.26% and the BOD5 by 57.14%. These values were lower than what was achieved generally by electrocoagulation; COD was reduced by >90% and BOD5 by >86%. By applying the simple process of electrocoagulation, the automobile industry should meet the regulatory requirements for discharge into water bodies or on land.