Comparative depollution of mecoprop aqueous solutions by electrochemical incineration using BDD and PbO2 as high oxidation power anodes

Abstract

The oxidation ability of the two most used high oxidation power anodes (i.e., anodes with high overpotential for O2 evolution), lead dioxide (PbO2) and boron-doped diamond (BDD), has been compared for the electrochemical incineration of solutions containing the herbicide mecoprop (MCPP) by using an electrolytic flow cell. The influence of several operating parameters such as current, liquid flow rate and MCPP concentration on the performance of both systems with a stainless steel cathode has been studied. Galvanostatic electrolyses always lead to complete mineralization due to the high amounts of effective hydroxyl radicals generated from water oxidation at each anode. The current efficiency using PbO2 is low, thus yielding extremely high energy consumption, while BDD anode exhibits faster oxidation rate and greater current efficiencies, along with a significantly lower energy cost. In this system MCPP disappears at a time similar to that required for overall mineralization, following a pseudo first-order kinetics that is typical of a constant excess of oxidizing hydroxyl radical. GC–MS analyses reveal that the electrochemical degradation pathway involves the same aromatic and carboxylic acid intermediates when using PbO2 or BDD anodes and that oxalic acid is the ultimate by-product prior to conversion to CO2.