Rapid removal of fungicide thiram in aqueous medium by electro-Fenton process with Pt and BDD anodes

Abstract

• Advanced oxidation processes (AOP) are effective for the wastewater treatment. • These processes are based to the production of power oxidizing hydroxyl radicals ( • OH). • Electro-Fenton (EF) process is one of the AOP widely used to treat water polluted by pesticides. • Constant rate for oxidation of thiram by • OH was found to be 5.54 × 10 9 M −1 s −1 . • Almost complete mineralization of thiram was reached by electro-Fenton with BDD anode. The electro-Fenton (EF) process was used to assess the electrochemical degradation of the fungicide thiram and its complete removal from water using an undivided electrolytic cell equipped with Pt or BDD anode and carbon felt cathode. Hydroxyl radicals, produced homogeneously in bulk solution from electrochemically generated Fenton's reagent ( • OH) and heterogeneously on the anode surface (M( • OH)) from oxidation of water, reacted with thiram leading to its fast oxidation. Oxidative degradation and mineralization kinetics were monitored by chromatographic analysis (HPLC) and total organic carbon (TOC) measurements. The electrochemical degradation of thiram by hydroxyl radicals followed a pseudo-first-order reaction kinetics with an absolute rate constant k abs(Thir) of 5.54 (±0.03) × 10 9 M −1 s −1 , determined by competition kinetics method. The TOC removal rate values were found significantly higher with BDD anode than Pt anode. Thus, almost complete mineralization (92%) of thiram solution was obtained when using BDD anode. These results highlight the major role of heterogeneous BDD( • OH) formed in the mineralization of thiram. The contribution of homogeneous • OH in mineralization of thiram was found relatively low due to its specific aliphatic structure. The efficiency of the EF process was evaluated by determining mineralization current efficiency and energy consumption per gram of TOC removed. Degradation by-products and inorganic ions, such as nitrate (NO 3 − ), nitrite (NO 2 − ), ammonium (NH 4 + ) and sulfate (SO 4 2 − ) formed during mineralization process, were identified by GC–MS and ionic chromatography analyses and a plausible mineralization pathway was proposed.