Degradation of diuron via an electrochemical advanced oxidation process in a microscale-based reactor

Abstract

Degradation of diuron, which is a toxic herbicide widely used in many countries, in aqueous solution was done in a microscale-based reactor using electrochemical advanced oxidation process (EAOP). A graphite sheet and a stainless steel were used as an anode and a cathode, respectively. Effects of pH and conductivity of the solution, applied current, and height of the microchannel, on the degradation of diuron were investigated. About 90% degradation of diuron could be achieved within 100 s of residence time in the reactor that was applied with 1 mA direct current. Moreover, the diuron degradation in water contaminated with anions, was also studied. The experimental results clearly suggested that the degradation takes place mainly by the interaction between diuron and hydroxyl radical generated via dissociation of water at the anode, although direct reduction of diuron by supplied electrons was also observed. The diuron degradation and reduction of total organic carbon (TOC) increase with increasing residence time and applied current, while the increase in the thickness of microchannel, conductivity and pH result in the decrease in diuron degradation. The ion contamination in diuron solution also reduces the degradation. All parameters directly influence the amount of hydroxyl radicals generated via EAOP. Additionally, formation and identification of intermediates were also studied by LC-MS/MS. Fifteen intermediates were identified under no anion and anion contamination. Two new intermediates were identified under nitrate ion contamination. The degradation generates many reaction intermediates, however, a simple reaction model employing 1st kinetics could represent the degradation well. Reaction pathway and mathematical model is proposed. Simulation result shows a good agreement with experimental data. Most of the degradation steps in the degradation pathway proceed at roughly the same rate that is much faster than the degradation rate achieved by other AOPs in conventional scale.