Bioturbation-Resilient phosphorus control in eutrophic sediments using industrial waste-derived calcium silicate hydrate.

Internal phosphorus (P) release from sediments remains a major obstacle to long-term eutrophication control in shallow urban waters. This study synthesizes a calcium silicate hydrate (CFA-CSH) from carbide slag and fly ash and evaluates its performance in regulating sediment P cycling. Structural analyses show a tobermorite-dominated phase with hierarchical porosity and abundant Ca-Si-OH sites, enabling rapid P capture through surface complexation and Ca-P mineral formation. Incubation experiments demonstrate that CFA-CSH effectively suppresses dissolved P and diffusive fluxes across the sediment-water interface and maintains stable immobilization capacity under both undisturbed and mildly bioturbated conditions. The stabilization arises from a coupled mechanism in which sustained Ca²⁺ release promotes hydroxyapatite-like mineral formation while the modified geochemical environment favors microbial assemblages that support P retention. The combined capping-injection application further establishes complementary barriers that limit resuspension and enhance long-term stability. Overall, waste-derived CFA-CSH offers a robust and scalable pathway for sediment P immobilization and provides a practical strategy for integrating industrial solid-waste utilization with eutrophication mitigation.