Vitamin C promoted refractory organic contaminant elimination in the zero-valent iron/peracetic acid system: Efficiency, mechanism and effects of various parameters.

The conventional zero-valent iron/peracetic acid (ZVI/PAA) system is severely limited owing to the passivation of ZVI and the low recovery of Fe2+. In this study, a reducing agent, vitamin C (H2A), was used for the first time to enhance the ZVI/PAA system as a way to improve its degradation performance. Under optimal conditions, the removal efficiency of the H2A/ZVI/PAA system was 82.9%, while that of the H2A/PAA and ZVI/PAA systems were only 19.0% and 25.6%. Free radical quenching and electron paramagnetic experiments (EPR) confirmed that CH3C(O)O•, •OH and CH3C(O)OO• were the major active species for acid orange 7 (AO7) degradation with contributions of 9.7%, 75% and 14.4%, respectively. The degradation mechanism was proposed through UV-vis full-wavelength scanning and chemical oxygen demand (COD) experiments. The removal of AO7 was not affected in the presence of Cl-, SO42- and HCO3-, while inhibition occurred with humic acid. ZVI exhibited excellent catalytic properties and stability, and the removal efficiency of AO7 exceeded 70% after three cycles. Additionally, the H2A/ZVI/PAA system showed good ability to remove AO7 in well water, lake water, river water and reservoir water, and the elimination efficiency of MO, DCF and ACE also exceeded 70%. Overall, this study contributes new cognition for enhancing the ZVI/PAA system to degrade contaminants, which is expected to achieve a cleaner water environment.