The Electrochemical Reaction Kinetics during Synthetic Wastewater Treatment Using a Reactor with Boron-Doped Diamond Anode and Gas Diffusion Cathode

A system of boron-doped diamond (BDD) anode combined with a gas diffusion electrode (GDE) as a cathode is an attractive kind of electrolysis system to treat wastewater to remove organic pollutants. Depending on the operating parameters and water matrix, the kinetics of the electrochemical reaction must be defined to calculate the reaction rate constant, which enables designing the treatment reactor in a continuous process. In this work, synthetic wastewater simulating the vacuum toilet sewage on trains was treated via a BDD-GDE reactor, where the kinetics was presented as the abatement of chemical oxygen demand (COD) over time. By investigating three different initial COD concentrations (C-0,C-1 approximate to 2 x C-0,C-2 approximate to 4 x C-0,C-3), the kinetics was presented and the observed reaction rate constant k(obs). was derived at different current densities (20, 50, 100 mA/cm(2)). Accordingly, a mathematical model has derived k(obs). as a function of the cell potential E-cell. Ranging from 1 x 10(-5) to 7.4 x 10(-5) s(-1), the k(obs). is readily calculated when E-cell varies in a range of 2.5-21 V. Furthermore, it was experimentally stated that the highest economic removal of COD was achieved at 20 mA/cm(2) demanding the lowest specific charge (similar to 7 Ah/g(COD)) and acquiring the highest current efficiency (up to similar to 48%).