Optimization of electrochemical degradation of organics considering the simultaneous effects of electroactive area and mass transfer on current modulation

Abstract

In the modulated current (MC) technique, the applied current is reduced during the course of the electrolysis, in order to maintain the process operating at limiting current (Ilim), corresponding to optimized charge and mass transfer conditions. However, despite the efficacy of MC for effluent treatment, a longer electrolysis time is required. This problem can be overcome using a turbulence promoter (TP) to enhance mass transfer and increase the reaction rate. In this work, an attempt was made to further improve the mass transfer, comparing electrolyses performed with plate and mesh BDD electrodes in the absence and presence of a TP. Instead of using the geometric area of the electrode (AG), the electrolyses were performed considering the electrochemical active area (AE) for determination of Ilim, avoiding overestimation of the current applied in the MC mode, since AE < AG, as observed here. The electrolyses were performed in a flow reactor, with phenol as a model organic compound. The process combining MC and a TP enabled 85% reduction of the energy consumption, corresponding to 24.4 kWh per kg of COD removed. This outstanding reduction was attributed to i) high mass transfer obtained due to the reactor design and use of a TP, and ii) 67% improvement of the current efficiency, due to improved mass transfer and the use of more accurate values of Ilim during the modulation. Finally, the efficacy of the MC+TP technique was validated in the degradation of a real wastewater.