Surface finishing wastewater having low pH (∼2) and high conductivity (>11 mS/cm) was treated by electrocoagulation (EC) or electrochemical Fenton (ECF) processes using sacrificial iron anodes. Under the same theoretical Fe dosage, the effects of electrolytic time, initial pH, and current density on the simultaneous removal of organic and heavy metal were investigated. A complete metal removal was achieved even at the low current density of 24.2 mA/cm2 and short electrolytic time of 4 min, whereas approximately 40% of chemical oxygen demand was removed. Increasing the electric current density did not improve removal efficiencies, but consumed more electric energy. Low current conditions produced a brown color sludge associated with ferric hydroxide. On the contrary, a greenish color sludge was created at a high current due to the formation of ferrous hydroxide. The formation of ferrous hydroxide impacted the treated water quality. The ECF was employed to overcome the low COD removal by the EC, achieving >67% of COD removal. The costs of ECF processes were slightly greater than that of chemical coagulation, but achieving a lot greater heavy metal removals. ECF process can be a promising method for simultaneous removal of heavy metal and organics from complex industrial wastewater.
Journal of the Taiwan Institute of Chemical Engineers 83, p.107-114