Detoxification mechanism of semi-coking wastewater by hydrogel-assisted SNAD process via iron‑mediated coordination adsorption: Performance, microbiota interaction, and molecular docking.

Semi-coking wastewater (SCWW) contains toxic compounds that threaten both human health and ecosystem integrity. In this study, an anaerobic ammonium oxidation (anammox)-based simultaneous partial nitrification, anammox, and denitrification (SNAD) process, enhanced with a novel polyvinyl alcohol/phytic acid/iron (PVA/PA/Fe) hydrogel carrier, was evaluated for treating actual SCWW. During long-term operation, the system achieved removal efficiencies of 90.8 % for ammonium nitrogen (NH4+-N) and 91.4 % for chemical oxygen demand (COD) in SCWW. The PVA/PA/Fe carrier facilitated sludge aggregation, enhanced extracellular polymeric substance secretion, and successfully enriched key functional microbes, encompassing anammox bacterium Candidatus Brocadia and phenol-degrading denitrifier Ottowia. Acute toxicity assays and nitrogen removal inhibition tests identified phenyl cyanate as a major toxicant in SCWW. Molecular docking confirmed its strong binding affinity for critical enzymes such as hydroxylamine oxidoreductase (Hao) and nitric oxide reductase (Nor). Adsorption experiments and density functional theory (DFT) calculations revealed that the PVA/PA/Fe effectively adsorbed phenyl cyanate via Fe-mediated coordination, with an adsorption capacity of 10.59 mg g-1. This capacity was sixfold greater than that of the unmodified carrier, substantially lowering the environmental concentration of phenyl cyanate and alleviating its inhibitory effect. Collectively, these findings provide a viable carrier-enhanced strategy for the biological treatment of SCWW.