Novel CaO2-magnetic biochar for synergistic recovery of inorganic and organic phosphorus from water: Mechanisms and potential for agricultural use

Recovering phosphorus (P) from wastewater can reduce non-point source pollution and alleviate phosphate fertilizer resource shortage. This study prepared a novel CaO 2 -magnetic biochar (CaMC) from wheat straw via a pyrolysis-precipitation integrated method to capture phytic acid (IP6) and inorganic phosphate (Pi) from solution and livestock wastewater, and its agronomic benefits were tested through wheat pot experiments with microbial community analysis. Maximum capture capacities of CaMC were demonstrated to be 294.2 and 133.1 mg g −1 for Pi (2248.30 mg/L→1512.80 mg/L) and IP6. The pseudo-second-order kinetics, intra-particle diffusion model, and Langmuir model depicted the adsorptive capture process best. Pi was captured mainly through electrostatic attraction and precipitation of Ca 5 (PO 4 ) 3 OH and Fe 3 (PO 4 ) 2 (OH) 2 , whereas IP6 removal was first oxidized to Pi via Fenton-like reactions and then adsorbed in the same way as Pi. In addition, the P capture capacity of CaMC reached up to 6.46 mg g −1 in the treatment of real livestock wastewater. Percent adsorption was 27.48% for total P, 22.41% for Pi (76.53 mg/L→59.38 mg/L), and 60.87% for organic P by CaMC. In wheat pot experiments, CaMC-P enhanced both total and available P levels in the soil compared to untreated soil and fertilizer controls. The addition of CaMC-P in soil resulted in a 14% increase in plant dry weight relative to the untreated control. Microbial analysis revealed an increased relative abundance of phosphate-solubilizing microorganisms ( Mortierella and Pseudomonas ) in soils treated with CaMC-P. These findings conclude that CaMC is an excellent adsorbent for P recovery in wastewater and for enhancing soil fertility.