Peroxydisulfate (PDS) is widely used in groundwater remediation systems. Previous studies investigated its activation by natural sediments under oxic conditions. However, the role of sediments Fe(II) species in PDS activation under anoxic conditions remains unclear. This work elucidated the activation of PDS and concurrent degradation of sulfamethoxazole (SMX) in sediments-based systems under various anoxic scenarios. The reaction of 10 g/L sediment suspensions with 2.2 mM PDS degraded SMX (10 & mu;M) up to 86.4%, leading to the decrease of SMX toxicity towards Photobacterium phoshoreum T3 spp. PDS activation by solid Fe(II) species in the sediments generated sulfate (SO4 & BULL;- ), hydroxyl (& BULL;OH), and organic matter-like (OM & BULL;) radicals. Kinetic modeling and radical quenching experiments substantiated that SO4 & BULL;? and OM & BULL; were the main contributing species to SMX degradation. Chemical extraction, Mo & BULL;ssbauer spectroscopy, and X-ray photoelectron spectroscopy analyses demonstrated that sediments surface-adsorbed Fe(II) predominantly interacted with PDS at a high molar Fe(II)/PDS ratio of 1.41, whereas structural Fe(II) underwent slower electron transfer reactions at a lower ratio of 0.75. This study provides novel insights into PDS activation by Fe(II)-bearing sediments and could advance the development of effective sediments-based PDS activation strategies for remediating contaminants in anoxic subsurface environments.

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