Phosphorus recovery from urine by CO2-activated biochar for sustainable slow-release fertilizer applications: Unveiling adsorption mechanisms by statistical physics modeling and predictive modeling with artificial neural networks

The global phosphorus crisis necessitates efficient phosphorus recovery, crucial for sustainable practices. This study introduces CAMLB, a CO2-activated Magnolia grandiflora leaf-based biochar, as an effective adsorbent for phosphorus capture from artificial urine and subsequently served as a sustainable slow-release fertilizer. Adsorbent characterization results implied the involvement of electrostatic attraction, ligand exchange, ion exchange, pore filling, hydrogen bonding, and surface precipitation in the adsorption process. Statistical physical outcomes reveals that the physical adsorption process is characterized by multi-ion adsorption, an inclined orientation, and an endothermic, reversible nature. Artificial neural network (ANN) models validate adsorption kinetics and isotherm data with high precision (R > 0.99). Additionally, spent biochar proves valuable as a slow-release fertilizer, promoting wheat germination and growth. Overall, this paper offers a circular economy approach for achieving the recycling of urine wastewater and agricultural waste and focuses on unraveling the mechanisms of phosphorus recovery.