Phosphorus adsorption and recovery from waste streams using biochar: review of mechanisms, modifications, and agricultural applications

This literature review investigated the efficacy of both unmodified and modified biochars as an adsorbent for phosphorus (P) capture from waste streams. The review focused on critical design aspects including the maximum phosphate removal adsorption capacities, influence of pH, coexisting ions, and pyrolytic conditions on P adsorption. The adsorption mechanisms, including electrostatic interactions, ion exchange, and complexation, were elucidated to provide insights into the underlying processes. The review revealed that the maximum phosphate removal adsorption capacity was influenced by factors such as the biochar type, surface properties, pyrolytic conditions, and presence of hydroxyl (–OH), carboxyl (–COOH) functional groups. The pH of the solution was identified as a crucial parameter affecting the efficiency of phosphate adsorption. Coexisting ions, notably carbonate anions, exhibited negative impacts on the phosphate removal process. Furthermore, this review discusses the characterization techniques used to assess biochar properties and adsorption mechanisms. Challenges related to biochar scalability, regeneration, stability, and metal leaching are addressed. Moreover, this review explored agricultural applications of P-laden biochar and found P-enriched biochar holds promise as a slow-release fertilizer for soil enrichment. This review highlights the role of biochar in promoting sustainable P management by integrating its application in wastewater treatment and agricultural reuse.