UV absorbance and electron donating capacity as surrogate parameters to indicate the abatement of micropollutants during the oxidation of Fe(II)/PMS and Mn(II)/NTA/PMS

In this study, the relative residual UV absorbance (UV₂₅₄) and/or electron donating capacity (EDC) was investigated as a surrogate parameter to evaluate the abatement of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes. In the Fe(II)/PMS process, due to the generation of SO₄^•- and •OH at acidic pH, UV₂₅₄ and EDC abatement was greater at pH 5. In the Mn(II)/NTA/PMS process, UV₂₅₄ abatement was greater at pH 7 and 9, while EDC abatement was greater at pH 5 and 7. This was attributed to the fact that MnO₂ was formed at alkaline pH to remove UV₂₅₄ by coagulation, and manganese intermediates (Mn(V)) were formed at acidic pH to remove EDC via electron transfer. Due to the strong oxidation capacity of SO₄^•-, •OH and Mn(V), the abatement of micropollutants increased with increasing dosages of oxidant in different waters in both processes. In the Fe(II)/PMS and Mn(II)/NTA/PMS processes, except for nitrobenzene (∼23% and 40%, respectively), the removal of other micropollutants was greater than 70% when the oxidant dosages were greater in different waters. The linear relationship between the relative residual UV₂₅₄, EDC and the removal of micropollutants was established in different waters, showing a one-phase or two-phase linear relationship. The differences of the slopes for one-phase linear correlation in the Fe(II)/PMS process (micropollutant-UV₂₅₄: 0.36–2.89, micropollutant-EDC: 0.26–1.75) were less than that in the Mn(II)/NTA/PMS process (micropollutant-UV₂₅₄: 0.40–13.16, micropollutant-EDC: 0.51–8.39). Overall, these results suggest that the relative residual UV₂₅₄ and EDC could truly reflect the removal of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes.