Sustainable phosphorus recovery from livestock digestate using ultrasonic solubilization and Zr ferrite adsorption

An integrated method was developed to enhance phosphate solubilization and recovery from anaerobic digestate of livestock manure by combining sonication pretreatment with zirconium ferrite (Zr ferrite) adsorption. The effects of sonication energy densities (0-74 Wh/L) on organic matter and phosphorus solubilization were investigated. Sonication significantly increased dissolved chemical oxygen demand (COD) and decreased pH, with COD levels plateauing at higher energy inputs. Pretreatment effectively converted non-bioavailable residual phosphorus (Residual-P) into bioavailable forms (NaHCO₃-P and NaOH-P), thereby improving phosphorus recovery potential. Adsorption equilibrium data were best fitted by the Langmuir-Freundlich model, yielding a maximum adsorption capacity of 28.08 mg/g for sonicated digestate compared to 18.27 mg/g for raw digestate. Kinetic analysis indicated pseudo-first-order behavior, highlighting concentration-dependent adsorption. SEM and EDS analyses further confirmed more uniform phosphate deposition on Zr ferrite after sonication. Beyond enhancing phosphorus recovery efficiency, this integrated process contributes to mitigating eutrophication risks and improving environmental safety by reducing uncontrolled phosphorus discharge. These findings demonstrate that the proposed approach is not only technically feasible but also environmentally beneficial, providing a sustainable pathway for nutrient management and circular wastewater treatment.