Cascading biochar strategies for phosphorus and potassium recovery and reuse

Abstract

The sustainable management of phosphorus (P) and potassium (K) is becoming increasingly critical due to resource depletion and inefficient nutrient utilization in agricultural systems. In this context, biochar-based cascade systems are gaining attention for nutrient recovery, recycling, and efficient utilization. This review evaluates recent advances in biochar-based phosphorus and potassium recovery systems, with particular emphasis on nutrient dynamics, recovery mechanisms, modification strategies, and current research challenges. Low fertilizer-use efficiency in conventional agricultural systems has resulted in substantial phosphorus (P) fixation in soils and potassium (K) leaching, leading to nutrient loss, environmental pollution, and depletion of natural resources. Biochar, produced through the thermochemical conversion of biomass. It serves as a nutrient source, with the potential to retain, adsorb, and gradually release nutrients over extended periods, owing to biochar’s large surface area, high porosity, and abundance of surface functional groups that provide chemical binding sites for nutrients. The feedstock type, temperature, and conditions under which the materials are pyrolyzed, as well as post-processing of the resulting product, are key factors that define the nutrient dynamics of biochar. To enhance the performance of biochar for nutrient availability and recovery, ongoing investigations are exploring approaches to modification, such as co-pyrolysis, metal doping, nano-biochar production, and biochar-microorganism interactions. The biochar cascade enables sequential nutrient recovery, transformation, and utilization, forming a closed-loop pathway for Phosphorus (P) and Potassium (K) management. These systems mobilize immobilized soil phosphorus and potassium through physical and biological mechanisms to improve crop fertility and productivity. Despite these benefits, several challenges remain, including performance variability, lack of standardization, potential environmental hazards, and limited long-term field validation of the results. Future research should focus on long-term field validation, standardized assessment protocols, economic feasibility, and life-cycle assessment to facilitate the large-scale implementation of biochar cascade systems within sustainable agricultural and circular bioeconomy frameworks.