The performance of Fe2+/ClO− system in advanced removal of fulvic acid under mild conditions

Fulvic acid (FA), a humics, was employed as a model representing bio-refractory soluble organic matter to investigate the performance of co-utilized FeSO4 and Ca(ClO)2 in advanced wastewater treatment. The removal efficiency of FA was greatly enhanced upon the synergistic effect of Fe2+ and ClO−, varying from 22% to 89% when the loading of ClO− varied from 1.6 to 80 mM at Fe2+/ClO−=0.5, TOC0 = 130 mg/L, and neutral pH. The results of Electron paramagnetic resonance (EPR) demonstrated the generation of hydroxyl radicals (•OH) in Fe2+/ClO− system, indicating that this treatment involved an advanced oxidation process. The contributions of both oxidation and coagulation showed that FA was removed incrementally by oxidation with the increase of reagent dosage. According to TOC, molecular weight distribution, UV–Vis, and FTIR results, on the one hand, FA was degraded and its aromaticity was reduced due to the breakage of the chemical bonds (such as amide and C−C bond) and the opening of aromatic rings by oxidative species (such as •OH and ClO−), which was benefit for coagulation; on the other hand, the degraded organics were further mineralized. The remained FA mainly contained alkyl substituted and/or CO conjugated aromatic ring structures as well as ether/ester structures.