In-situ synthesis of lanthanum-coated sludge biochar for advanced phosphorus adsorption

Eutrophication and phosphorus scarcity pose significant environmental and resource management challenges, necessitating the development of efficient phosphorus removal and recovery technologies. In this study, lanthanum hydroxide-coated sludge biochar adsorbent was prepared via in-situ liquid precipitation and its phosphorus adsorption performance was evaluated. The adsorbent obtained under the optimized conditions, i.e., 5:1 ratio of La to sludge and 550 °C of annealing temperature (designated as La-C-550), exhibited a maximum phosphorus adsorption capacity of 76.4 mg-P/g at 25 °C. Mechanistic analysis revealed a multilayer adsorption process involving both physical and chemical interactions, with chemical adsorption primarily driven by the complex substitution of hydroxyl by phosphate. La-C-550 demonstrated stable performance across a pH range of 3-7, and maintained resilience against interference from common anions and humic acid. In continuous flow tests using actual secondary effluent, the adsorbent stably reduced phosphorus concentrations to below 0.1 mg-P/L, complying with the Chinese Surface Water Environmental Quality Class II standards. These results underscore the potential of La-C-550 as a cost-effective and highly efficient material for phosphorus removal in wastewater treatment applications.