Electro-Fenton approach for highly efficient degradation of the herbicide 2,4-dichlorophenoxyacetic acid from agricultural wastewater: Process optimization, kinetic and mechanism

Abstract

2,4-Dichlorophenoxyacetic acid (2,4-DPAA) as a commonly used herbicide in agricultural farms causes severe contamination of groundwater and surface water. Herein, a treatment process based on the electro-Fenton (EF) technique was developed for efficient removal of 2,4-DPAA from agricultural wastewater. Response surface methodology (RSM) was employed to optimize the operation conditions and modeling the developed process. The best removal efficiency of 99.2 was achieved at solution pH of 3, initial 2,4-DPAA concentration of 2.6 mg L�1, H2O2 dosage of 470 µL L�1, the current density of 3.5 mA cm�2, and reaction time of 7.5 min, which is in good accordance with the predicted removal efficiency of 98.6 by the model. The developed process was applied successfully for removal of 2,4-DPAA from agricultural wastewater with the actual removal efficiency of 93.7. The values of coefficients of determination (R2), predicted R2 and adjusted R2 were found to be 0.9775, 0.9268, and 0.9690, respectively. Analysis of variance (ANOVA) was conducted to evaluate the competence of the developed model. The obtained high F-value of 114.14 and the very low P-value of <0.0001 confirm that the model is highly significant. The electrical energy consumption was found to be 0.058 kWh.m�3. Employing the radical scavengers and the control experiments based on electrocoagulation and the Fenton process, the main mechanism for 2,4-DPAA degradation is revealed by the in-situ generation of hydroxyl radical throughout the EF treatment process. The kinetic of the developed model followed a pseudo-first-order reaction with a rate constant of 0.4746 min�1. © 2021 Elsevier B.V