Min Chen, Xichang Wu, Yu Wang, Jie Wang, Chaochan Li, Tianhua Yu, Anping Wang
Excessive nitrogen and phosphorus in aquatic systems trigger eutrophication and environmental contamination. Herein, Ca(OH)2-modified Camellia oleifera shell biochar was fabricated as an adsorbent for NH4+ and PO43− removal, with the effects of contact time, temperature, initial concentration, and pH on adsorption performance investigated, and the mechanisms clarified via kinetic/isothermal models combined with FT-IR and XPS characterizations. Results showed that NH4+ and PO43− adsorption both fit the pseudo-second-order kinetic model, indicating chemisorption dominance. NH4+ adsorption complied with both Langmuir and Freundlich models (monolayer-multilayer coexistence), while PO43− adsorption followed only the Freundlich model (predominant multilayer adsorption). Acidic conditions and low temperatures favored PO43− uptake, whereas alkaline conditions promoted NH4+ adsorption, with adsorption capacity showing a decrease-then-increase trend with temperature elevation. Notably, the modified biochar maintained favorable performance in complex swine wastewater. Mechanistically, NH4+ removal was dominated by ion exchange, while PO43− removal relied on the synergy of ion exchange and precipitation, with precipitation as the primary pathway. This work provides a cost-effective strategy for nutrient removal from wastewater via agricultural waste valorization.