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 Fe. In this study, a reducing agent, vitamin C (HA), 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 HA/ZVI/PAA system was 82.9%, while that of the HA/PAA and ZVI/PAA systems were only 19.0% and 25.6%. Free radical quenching and electron paramagnetic experiments (EPR) confirmed that CHC(O)O•, •OH and CHC(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, SO and HCO, 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 HA/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.