Iron ores with contrasting redox properties drive iron biogeochemical cycling to enhance acesulfame and nutrients removal in constructed wetlands.

Iron minerals have attracted considerable attention for their potential to enhance the removal of nutrients and emerging contaminants within water treatment. However, how the intrinsic redox state of iron in minerals governs pollutant attenuation remains insufficiently understood. In this study, Fe(III) (hematite) and Fe(II) minerals (pyrite) were employed to construct constructed wetlands (CWs) for the simultaneous removal of the artificial sweetener acesulfame (ACE) and nutrients. According to substrate characterization and soluble iron monitoring, the observed elemental changes indicated the occurrence of Fe(III)/Fe(II) cycling and its involvement in the removal of ACE and nutrients. Moreover, the Fe(III)-based CWs exhibited markedly higher iron redox activity than Fe(II)-based CWs. Correspondingly, Fe(III)-based CWs achieved higher removal performance of pollutants than Fe(II)-based CWs, with average removal efficiencies of 32.3% for total nitrogen, 88.7% for total phosphorus, and 44.8% for acesulfame, respectively. Simultaneously, Fe(III) minerals promoted the formation of iron plaque on roots, suggesting enhanced iron cycling in the rhizosphere. Microbial community analysis further revealed diverse communities associated with iron transformation, including 13 genera capable of Fe(II) oxidation and 43 genera involved in dissimilatory iron reduction in both substrates and rhizosphere zones. These taxa mediated electron transfer processes that linked iron redox transitions with pollutant transformation. Moreover, the intrinsic redox state of iron minerals established the contrasting electron-flow regimes during iron cycling. This work provides new insight into the role of iron cycling in pollutant removal as an endogenous metabolic driver.