Chlorpyrifos removal from aqueous solution through sequential use of coagulation and advanced oxidation processes: By-products, degradation pathways, and toxicity assessment

Abstract

Chlorpyrifos (CPF), as a highly toxic pesticide, is extensively consumed in the agricultural industry and may cause environmental damage. The aim of present study was to evaluate the potential usage of Fe(VI) and Fe(VI)/PMS processes for CPF oxidation in an aqueous solution. The study was conducted in two phases including coagulation and flocculation, as well as advanced oxidation process (AOP). In the first phase, the coagulation process, as a prevalent pretreatment for AOP, was performed for turbidity removal by two types of coagulants, K 2 FeO 4 and FeCl 3 . K 2 FeO 4 showed the best performance as a coagulant at acidic pH=3.0 with an efficiency of 97.47%, while FeCl 3 revealed the highest efficiency (95.79%) at alkaline pH=8.01. However, only the supernatant from the Fe(VI) coagulation process was selected for the next phase analysis. In the next phase (AOP), the results showed that the removal efficiency of Fe(VI)/PMS system was higher than that of Fe(VI) process within the entire pH range. Under optimum conditions ([Fe(VI)]:[PMS]=5:1, pH=7.0, and CPF=2 mg/L), 94.75% removal efficiency was achieved by Fe(VI)/PMS, while it was 82.80% for Fe(VI) alone. The CPF degradation pathways using Fe(VI)/PMS process were proposed, including the P=S bond oxidation, the C–O bond cleavage, diethylation as well as reaction of hydroxyl substitution, leading to the generation of six products. The ECOSAR simulation program showed that the chronic and acute toxicity of CPF degradation byproducts in the Fe(VI)/PMS system relatively decreased. In summary, the study indicated that the Fe(VI)/PMS oxidation is a compatible and efficient technique for removing CPF from aqueous media. • The CPF degradation processes by Fe(VI) and Fe(VI)/PMS was systematically studied. • The optimum conditions were achieved for CPF degradation. • By-products of CPF degradation were detected using LC/MS/MS. • The CPF degradation mechanism was presented based on the oxidation products. • The CPF and its oxidation byproducts toxicity were predicted by ECOSAR program.