Dual-targeted phosphorus and COD removal by engineered amine-modified zeolite with pH self-regulation and competitive adsorption selectivity

Elevated total phosphorus (TP) and chemical oxygen demand (COD) drive dissolved oxygen depletion and black-odorous water formation in surface waters. To address this dual contamination challenge, this study engineered an amine-modified zeolite (AMZ) adsorbent. The functionalization process was meticulously refined using orthogonal experimental design, systematically optimizing critical parameters like amine type, concentration and temperature to maximize performance. The resulting AMZ demonstrated exceptional co-removal capabilities, achieving > 90% TP and > 80% COD removal efficiency across an exceptionally wide pH range (3-10) in both single-component and competitive binary systems. Crucially, AMZ uniquely stabilized treated effluent pH near neutrality (7.2 ± 0.2), a significant operational advantage. NaCl-enabled regeneration maintained > 90% TP and > 80% COD removal efficiency over multiple cycles. AMZ demonstrated robust performance in authentic wastewater matrices. The cost-performance advantage of AMZ becomes evident when benchmarked against commercial alternatives. SEM revealed a multilayered flake morphology enhancing active site accessibility. This study provides the first demonstration of site-specific selectivity in competitive adsorption of TP and COD on amine-functionalized zeolite: electrostatic sites (quaternary ammonium groups) favored HPO₄^2- binding, while ion-exchange sites exhibited selectivity toward phthalate anions (dominant COD component). This work validates AMZ's applicability in complex water remediation scenarios.