Degradation of pesticide mixture by electro-Fenton in filter-press reactor

Abstract

The efficiency of a prototype equipped with a dimensionally stable anode (DSA) and a carbon felt cathode was analysed by means of H2O2 production and removal of the herbicides diuron (DIU) and glyphosate (GLY) from 0.05 M Na2SO4 solutions, pH 3.0, by electrochemical oxidation (EO), EO with H2O2 electrogeneration and electro-Fenton (EF). Mineralisation current efficiencies and specific energy consumption were also determined. The best performance under galvanostatic conditions was found to be that of the EF, with 1 mM of Fe2+, compressed air flux of 1 L min–1 and current intensity of 1.00 A, for 180 min of treatment, 34% of mineralisation, with 5% current efficiency and specific energy consumption of 0.85 kW h g–1 of total organic carbon was found. A maximal accumulated concentration of 78 mg L–1 of electrolysed H2O2 was achieved in 60 min, and the concentrations of DIU and GLY were reduced by 8% and 94%, respectively. There is a good correlation between the studied flux dispersion in the residence time distribution and the conversion rate verified on degradation, with 100% for GLY and 66.2% for DIU. Two organic by-products as well as short chain carboxylic acids, namely formic, citric and oxalic acid, were detected by LC–MS, and therefore, DIU and GLY degradation mechanisms were proposed.