Layered Double Hydroxides/Biochar Composites as Sustainable Adsorbents for Phosphorus Removal in Water: Recent Trends and Perspectives

Phosphorus (P) is one of the important factors leading to water eutrophication. Adsorption is widely applied as an effective strategy for P removal in water bodies. Recently, layered double hydroxide/biochar (LDH-BC) composites as adsorbents for P removal have received increasing attention for their outstanding adsorption performance and technical economy. This review examined the application of LDH-BC composites for P removal and recovery from aqueous environments. It detailed the adsorption mechanisms that underpin the high affinity of LDH-BC for phosphate ions. The synthesis methods, including postpyrolysis, prepyrolysis, and hydrothermal approaches, were systematically compared, highlighting the effects of biomass source, pyrolysis conditions, metal types and proportions, and LDH loading ratios on adsorption performances. The environmental factors such as pH, temperature, competing ions, and hydraulic conditions were discussed for their influences on adsorption efficiency. The review also covered practical applications in diverse wastewater matrices, resource recovery strategies, and techno-economic and life cycle assessments. Finally, current challenges and future directions for enhancing the sustainability and scalability of LDH-BC-based P management were outlined.