Removal of the herbicide monolinuron from waters by the electro-Fenton treatment

The removal of the phenylurea herbicide monolinuron (MLN) from water was investigated by the electro-Fenton method, based on the electro-catalytic in situ continuous production of large amounts of the strong oxidant hydroxyl radicals. The effect of several parameters, including the Fe2+ initial concentration, applied current and type of anode (Pt and boron-doped diamond - BDD), on the MLN degradation kinetics was evaluated. MLN decay kinetics was monitored by HPLC, fitting a pseudo first-order reaction, leading to a rate constant kabs = (3.1 ± 0.2) × 109 M−1 s−1. Several oxidation intermediates species were identified and followed by HPLC and GC–MS. A quasi complete mineralization rate (98% TOC removal) of MLN solution was reached after 8 h of treatment on BDD anode with low energy consumption. Identification of carboxylic acids and inorganic ions was carried out by HPLC and ionic chromatography analyses. Based on identification of aromatic and aliphatic intermediates, inorganic end-products and TOC removal value, a complete MLN mineralization pathway was also proposed.