Fe electrocoagulation technology for highly-efficient p-arsanilic acid removal from water: Feasibility and mechanisms

Conventional oxidation methods are effective for the removal of p-arsanilic acid (p-ASA) in water but are limited by complicated process. Herein, Fe electrocoagulation with Fe as anodes was used to efficiently remove p-ASA with 100% total arsenic removal within 60 min (1.75–20 A/m2). Current density significantly influenced sludge production, anode loss, and energy consumption (p-value < 0.05). Kinetic analyses showed a decline in arsenic removal rate with increasing initial pH (4.0–10.0). The changes in main elements of p-ASA (As and N) were analyzed to identify intermediate products using UPLC-Q-TOF-MS, HPLC-ICP-MS, and spectrometry. Hydroxyl radicals were confirmed as the primary reactive oxygen species. The active sites of p-ASA molecules were predicted by theoretical calculations and reaction paths were proposed. The toxicity of Fe-EC effluent was effectively reduced according to the analyses of ECOSAR and E. coli colonies method. The possible mechanisms of p-ASA removal, including oxidative degradation, electrostatic attraction, and ligand complexation, were proposed. Real water containing a p-ASA concentration of 250 μg/L was treated for 48 h using continuous-flow Fe-EC and arsenic concentrations of 2–30 μg/L in effluent were obtained. Overall, Fe-EC was a simple, cost-effective, and eco-friendly technology for the removal of p-ASA.