<i>In Situ</i> Peroxymonosulfate Activation Generates Reactive Species in Iron-Containing Sludge Systems for Efficient Sludge Dewatering and Emerging Organic Contaminant Degradation

Peroxymonosulfate-based advanced oxidation technologies (PMS-AOTs) are an effective sludge treatment strategy for sludge volume reduction and treatment cost saving, but rely on high external energy and/or material input. We achieved <i>in situ</i> PMS activation driven by intrinsic iron (Fe) minerals in sludge rather than exogenous catalysts. Sufficient PMS doses (i.e., 100 mg g^-1 total solids (TS)^-1) reactivated intrinsic Fe minerals by acidifying the sludge matrix and partially dissolving passivated Fe phases, effectively converting inert Fe into active and mobile species. This action triggered a self-reinforcing cycle, where abundant Fe(II) in high-Fe sludge (>30 mg Fe g^-1 TS^-1) donated electrons for homolytic PMS activation, generating a radical-dominated pathway. Continuous Fe(III) reduction via PMS intermediates and sludge sulfur-based groups reinforced the Fe(III)/Fe(II) redox cycle, enabling persistent Fenton-like radical generation. Conversely, low-Fe sludge exhibited a limited Fe supply and fewer reactive Fe sites, shifting the PMS reaction toward a less efficient nonradical pathway. Accordingly, high-Fe sludge achieved markedly superior performance, evidenced by a 41.0% lower water content of sludge cake and a 1.2-fold higher sulfamethoxazole (SMX) removal compared with low-Fe sludge. A pilot-scale experiment confirmed stable sludge dewatering and SMX removal. Collectively, the autonomous activation of PMS by sludge-intrinsic Fe minerals presents a new direction for sustainable sludge treatment, notable for its simplicity, stability, and economic effectiveness.