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Recently, sulfidation of zerovalent iron (S-ZVI) has gained increasing attention due to its merits to mediate the electron transfer from Fe⁰ core to reactants at the water-particle interface. However, few studies have attempted so far to use the unique properties of S-ZVI to activate peroxydisulfate (PDS) under both oxic and anoxic conditions. Hence, in this study, the performance of S-ZVI in activating PDS was systematically evaluated at various conditions. As expected, under oxic conditions, S-ZVI could enhance the acetaminophen (ACT) removal rate by 2.4–5.1 folds compared to unmodified ZVI, and this enhancing effect works well over the tested initial pH range of 3.0–8.5. Likewise, under anoxic conditions, S-ZVI still performed better than unmodified ZVI. But interestingly, both ZVI and S-ZVI achieved better PDS activation with the absence of O₂, despite in which comparable or much less Fe⁰ were consumed. This …