Removal of chlorpyrifos pesticide by advanced oxidation process of ferrate/peroxymonosulfate from water

Abstract

Chlorpyrifos (CPF), an organophosphate pesticide, has been widely used in the agricultural industry and may cause environmental damage. The present study was aimed to evaluate the potential application of Fe(VI) and Fe(VI)/PMS processes for oxidation of CPF in water treatment. Hence, this study was performed in two phases including coagulation and flocculation process and advanced oxidation process (AOP). In the first phase, the coagulation process was performed for turbidity removal by two types of coagulants, potassium ferrate (K2FeO4) and ferric chloride (FeCl3). In this phase, using a central composite design (CCD), the combined effect of four variables including initial turbidity, initial pH, coagulant dose and contact time was investigated. The supernatant from both coagulants were then transferred to the next phase for further comparison and analysis. In the AOP phase, the effect of Fe(VI) and Fe(VI)/PMS oxidants were investigated separately. In the first phase (coagulation and flocculation), K2FeO4 showed the best performance as a coagulant at acidic pH (pH 3.0) with an efficiency of 97.47%, while FeCl3 showed the highest efficiency (95.79%) at alkaline pH (pH 8.01). In the next phase (AOP), the results showed that the degradation efficiency of Fe(VI)/PMS process after both coagulation processes (by Fe(VI) and FeCl3) was higher compared to Fe(VI) process at all pHs. However, the highest removal efficiency in both processes was obtained at pH=7. Also, by examining the reaction kinetics, it was found that after the coagulation process by Fe(VI), the removal rate in the Fe(VI)/PMS process is 1.7 times higher than the Fe(VI) process. While after the coagulation process by FeCl3, the removal rate in the Fe(VI)/PMS process is 1.5 times higher than the Fe(VI) process. Due to the high efficiency of the Fe(VI)/PMS system after the Fe(VI) coagulation process, subsequent experiments were performed on this process. The degradation pathways of CPF by Fe(VI)/PMS system were proposed including the P=S bond oxidation, the C–O bond cleavage, diethylation and hydroxyl substitution reaction, leading to the formation of six products which were detected by LC/MS/MS. The ECOSAR simulation program showed that the acute and chronic toxicity of CPF degradation products in the Fe(VI)/PMS process was relatively decreased. This study has indicated that Fe(VI)/PMS oxidation is an efficient technique for the CPF removal from water. Key words: Water treatment; Advanced oxidation; Chlorpyrifos; Ferrate(VI); Peroxymonosulfate; Toxicity assessment