Applicability of electrochemical oxidation using diamond anodes to the treatment of a sulfonylurea herbicide

In this work, the electrolysis of chlorsulfuron (ClSF, a sulfonylurea herbicide) with conductive-diamond anodes is studied. The influences of the nature of the supporting electrolyte (0.05 mol dm−3 NaCl and Na2SO4), the applied current density (30 and 100 mA cm−2) and the initial herbicide concentration (20,50 ad 100 mg dm−3) have been evaluated. Total mineralization of the herbicide was attained regardless of the supporting electrolyte medium used, although electrolyte clearly influenced on the efficiency and rate of the oxidation process. Likewise, the process was found to be more efficient at low current densities. Results point out the importance of mediated electrochemical processes in the removal of ClSF. This influence was confirmed by additional tests in which the electrolysis was combined with UV light or ultrasound irradiation: the use of UV irradiation results in a less efficient process, while US improves importantly the rate of the mineralization as compared to the single electrolytic process. The strong oxidation conditions of electrolysis leads to the formation of reaction intermediates (2-amino-4-methoxy-6-methyl-1,3,5-Triazine, 2-chlorobenzenesulfonamida and oxalic acid) in agreement with the mechanisms proposed in the literature for other AOPs.