Advanced treatment of biologically pretreated coking wastewater by electrochemical oxidation using boron-doped diamond electrodes

Electrochemical oxidation is a promising technology to treatment of bio-refractory wastewater. Coking wastewater contains high concentration of refractory and toxic compounds and the water quality usually cannot meet the discharge standards after conventional biological treatment processes. This paper initially investigated the electrochemical oxidation using boron-doped diamond (BDD) anode for advanced treatment of coking wastewater. Under the experimental conditions (current density 20-60 mA cm(-2), pH 3-11, and temperature 20-60 degrees C) using BDD anode, complete mineralization of organic pollutants was almost achieved, and surplus ammonia-nitrogen (NH3-N) was further removed thoroughly when pH was not adjusted or at alkaline value. Moreover, the TOC and NH3-N removal rates in BDD anode cell were much greater than those in other common anode systems such as SnO2 and PbO2 anodes cells. Given the same target to meet the National Discharge Standard of China, the energy consumption of 64 kWh kgCOD(-1) observed in BDD anode system was only about 60% as much as those observed in SnO2 and PbO2 anode systems. Further investigation revealed that, in BDD anode cell, organic pollutants were mainly degraded by reaction with free hydroxyl radicals and electro-generated oxidants (S2O82-, H2O2, and other oxidants) played a less important role, while direct electrochemical oxidation and indirect electrochemical oxidation mediated by active chlorine can be negligible. These results showed great potential of BDD anode system in engineering application as a final treatment of coking wastewater. (c) 2009 Elsevier Ltd. All rights reserved.