Treatment of waste sludge: a comparison between anodic oxidation and electro-Fenton processes.

BACKGROUND Electrochemical methods, as one of the advanced oxidation processes (AOPs), have recently been applied to remove different contaminants from water and wastewater. This study compares the performance of anodic oxidation (AO) and electro-Fenton (EF) methods on waste sludge treatment. METHODS This experimental study was performed on real sludge and the effect of operating parameters such as solution pH, operating time, current density, supporting electrolyte and hydrogen peroxide concentration were investigated in a batch reactor. For determination of oxidation and treatability of the sludge, chemical oxygen demand (COD) and total coliform (TC) removal were examined. Pb/PbO2 and iron electrodes respectively for AO and EF were applied. RESULTS Experimental data indicated for both AO and EF as the operating time and current density increased, COD removal increased. pH=4.0 and 3.0 and current density=1.75 and 2 A respectively for AO  and EF and the concentration = 57.2 mMol of hydrogen peroxide for EF were measured as the optimum amounts of these variables. The removal efficiency of COD in AO and EF process was 76% and 72%, respectively. Of course, the efficiency of EF in TC removal was better and the percentage of TC removal in 60 min for AO and EF was 99.0% and 99.9%, respectively. The amounts of consumed electrical energy for AO and EF were 8.6 and 28.0 kWh kg-1 COD, respectively. CONCLUSIONS AO was more effective in treatment and mineralization of waste sludge and TC removal than EF in terms of environmental economical features.