Electrochemical advanced oxidation of 2,4-D herbicide and real pesticide wastewater with an integrated anodic oxidation/heterogeneous electro-Fenton process

Abstract

Pesticide wastewater is accused of polluting receiving waters with toxic and non-biodegradable organic pollutants. The present study has developed an integrated electrochemical oxidation process based on PbO2 anodic oxidation and Fe/SBA-15 heterogeneous electro-Fenton (PbO2/EF-(Fe/SBA-15)) for synergistic treatment of pesticide wastewater. PbO2 electrocatalyst was prepared by anodic deposition method and Fe/SBA-15 catalyst was synthesized by incipient wetness impregnation method. To optimize and model the removal of 2,4-D, a quadratic mathematical model by orthogonal central composite design (CCD) was proposed and validated. In optimal conditions including solution pH = 5, H2O2 concentration = 2000 mg/L, applied current = 10 mA/cm2, Fe/SBA-15 dose = 1.25 g/L and 2,4-D concentration = 30 mg/L, the experimental removal efficiency of 2,4-D after 35 min of reaction in the PbO2/EF-(Fe/SBA-15) process was 99.85 %. Moreover, the kinetics of 2,4-D removal in the integrated PbO2/EF-(Fe/SBA-15) process was about 3.84 times faster than the separate PbO2 anodic oxidation, confirming a remarkable degradation synergy. The mineralization of 2,4-D was confirmed by LC-MS and TOC analyses, and considering the identified intermediates, the possible degradation pathways of 2,4-D to CO2 and H2O were suggested. Real pesticide wastewater treatment was studied under optimal conditions. COD removal efficiency in PbO2/EF-(Fe/SBA-15) process and PbO2 anodic oxidation was 71.2 % and 32.5 %, respectively. Also, the energy consumption (EC) of these two processes was 17 kWh/kg COD and 38 kWh/kg COD, respectively. The results of this study suggest the integrated PbO2/EF-(Fe/SBA-15) process is a practical and cost-effective process for non-biodegradable pesticide wastewater treatment.