Tannery wastewater treatment after activated sludge pre-treatment using electro-oxidation on inactive anodes

Currently, electrochemical oxidation is a very efficient method to treat many types of wastewaters. Under the effects of electrical current, toxic or non-biodegradable substances will be oxidized to become biodegradable or completely oxidized to CO(2)and H2O. With the strengthening of environmental discharge legislations, tannery wastewater may have a negative effect on the environment because of its high pollution levels. In this study, for the first time, the tannery wastewater treatment after the activated sludge process digestion was carried out using electrochemical oxidation by SnO2/Ti and PbO2/Ti inactive anodes. Effects of current density, pH, stirring rate and reaction time on the pollutants removal efficiencies of tannery wastewater were studied. The results showed that SnO2/Ti and PbO2/Ti anodes can effectively remove over 80.0% of the color, chemical oxygen demand and total nitrogen in tannery wastewater after 90 min of reaction time at a current density of 66.7 mA/cm(2). SnO2/Ti anodes gave higher pollutants removal efficiency in base environments, while PbO2/Ti anodes offered higher pollutants removal efficiency in acidic environments. The current density and stirring rates significantly affected pollutant removal efficiencies, and the concentration of pollutants in the effluent decreased as reaction time was increased. In general, SnO2/Ti anodes were found to be more effective than PbO2/Ti anodes in the pollutants removal efficiency and energy consumption of tannery wastewater treatment. Graphic abstract