Electrochemical oxidation treatment of coal tar wastewater with lead dioxide anodes

In this study, coal tar wastewater was treated by electrochemical oxidation technology using lead dioxide anodes. The influence of operating parameters, including applied current density, electrode gap and initial pH value, on the removal ratio of chemical oxygen demand (COD) was investigated. The results demonstrated that the COD removal ratio reached 90.5% after 3.5 h electrolysis with the current density at 3 A dm^-2 and electrode gap at 1.0 cm. Correspondingly, the COD decreased from 5,125 mg L^-1 to 487 mg L^-1, which fitted the wastewater discharge standards of China, and the specific energy consumption (SEC_COD) was 35.3 kWh kg_COD ^-1. Not only was the COD removal ratio only 77.1% after 2 h electrolysis but the BOD₅/COD ratio of the wastewater reached 0.44, which could be biochemically treated, and the SEC_COD decreased by 34.3%. Moreover, the main composition of pristine wastewater before and after 2 h electrolysis was analyzed by GC-MS, and the disappearance of macromolecules (such as ethyl-2-pyrenemethanol) and the production of small molecules (such as propane-1,3-diol) could improve the biodegradability of the wastewater. Therefore, electrochemical oxidation for 2 h is a promising alternative for pretreatment of coal tar wastewater prior to biological treatment.