Fe2+, Fe3+, Co2+ as highly efficient cocatalysts in the homogeneous electro-Fenton process for enhanced treatment of real pharmaceutical wastewater

Abstract

The electro-Fenton process (EFP) has been known as an effective process with highly outstanding oxidation power. In this study, the real pharmaceutical wastewater was successfully mineralized via EFP by using boron-doped diamond (BDD) anode and carbon-fiber brush cathode (CFB) with Fe2+/Fe3+/Co2+ cocatalysts. The effect of various parameters, including the electrode, ratio of cocatalysts, current density, pH, and O2 flow rate, was investigated. The TOC and COD removal efficiencies of 92% and 93%, respectively, were achieved. For the increase in biodegradability, BOD5/COD ratio increased from 0.1 to 0.69 after 2 h in the presence of Fe2+/Fe3+/Co2+ cocatalysts under optimal conditions in a batch experiment (current density of 17 mA cm−2, initial pH of 3, a Fe2+/Fe3+/Co2+ ratio of 1:1:2, O2 flow rate of 0.5 L min−1). In comparison, TOC and COD removal efficiencies were reached 81% and 85% after 10 h of reaction in a continuous-flow condition, respectively. The oxidation of pharmaceutical organic pollutants was mainly found by the electrochemically produced hydroxyl (OH) and sulfate (SO4−) radicals, followed by pseudo-first-order kinetics. Hence, EFP demonstrated the feasibility of potential technology for the treatment of real pharmaceutical wastewater.