Fe2+ has been commonly selected to activate peroxydisulfate(PDS) for sulfate radical(SO4-·) generation because of its eco-friendly, cost-effective, and high activity characteristics. However, Fe2+ can be rapidly oxidized to Fe3+ in the reaction, leading to poor utilization of iron for PDS activation. Further, a fairly high concentration of Fe2+ is generally required and may cause iron sludge production and secondary pollution. In this study, a minute Fe2+-activated PDS system induced by bisulfite(BS) was used to degrade paracetamol(APAP) in water. The results showed that the Fe2+-PDS system could be enhanced by the circulation of Fe2+-Fe3+ with the injection of BS and by keeping Fe2+ at a high concentration. Under the optimal conditions(PDS=0.6 mol·L-1; BS=0.4 mol·L-1; Fe2+=10 μmol·L-1; pH=4), 100% APAP(4 μmol·L-1) was removed within 180 s. The degradation rate of APAP increased with the increase in BS(0-0.6 mmol·L-1) and PDS(0.2-1.5 mmol·L-1) concentration, and a modest Fe2+ concentration could accelerate APAP removal. Co-existing substances inhibited the APAP removal and followed the order of HCO3->HPO42->Cl->NO3->humic acid(HA). Based on the quenching experiments and electron paramagnetic resonance spectroscopy test, SO4-· was shown to be the primary reactive species for APAP decomposition in the BS-Fe2+-PDS process. Three-dimensional fluorescence spectroscopy revealed that APAP intermediates had fluorescence characteristics. Moreover, five intermediates were identified, and the probable APAP degradation pathways were proposed. The removal efficiencies of APAP were lower in real waters than that in ultrapure water. Nevertheless, the removal effect was greatly improved after a prolonged reaction time. All results indicated that the BS-Fe2+-PDS system could be a promising method for organic pollutant treatment.
Keywords: bisulfite; degradation; minute Fe2+; paracetamol; peroxydisulfate (PDS); sulfate radical(SO4-·).