Peroxydisulfate (PDS) activation by Fe2+ has proven to be a promising method to abate emerging organic contaminants by generating reactive oxidation species. Nevertheless, this process may only achieve good decontamination performance under acidic conditions, which has markedly limited its application in real practice. To address this issue, we comprehensively investigated the performance of the Fe2+/PDS process toward some probe contaminants at different pH levels and explored the potential change in reactive oxidative species and the influence of oxygen. Both SO4-· and Fe(Ⅳ) were identified to be involved in the Fe2+/PDS process, and the types of these oxidative species did not change with varying pH values. Although dissolved oxygen could compete with PDS for Fe2+, especially at high pH values, this competition process was not the major reason for the declined performance of the Fe2+/PDS process, since 37.6%-100% of PDS could also be activated with the presence of oxygen. Instead, the overdosing of Fe2+could greatly inhibit carbamazepine removal, indicating that the nonproductive consumption of reactive oxidants by Fe2+should account for the declined performance of Fe2+/PDS under environmentally relevant pH conditions. Accordingly, the feasibility of applying zero-valent iron and sulfidated zero-valent iron was further evaluated, and the formation of corrosion products was characterized using X-ray absorption fine structure spectroscopy. All these findings will improve our understanding about the Fe2+/PDS process and thus facilitate its application.
Keywords: emerging organic contaminants; environmentally relevant pH conditions; ferrous iron; peroxydisulfate; sulfidation treatment; zero-valent iron.