Closed-Loop Process for Phosphorus Recovery from Poultry Litter

The anticipated depletion of phosphorus (P), a critical mineral, within the next 65−90 years highlights the urgent need to explore alternative sources. This study presents a three-step sustainable approach for P recovery from poultry litter, utilizing chemical leaching followed by precipitation and adsorption. A response surface methodology (RSM) optimization tool was used to minimize chemical oxygen demand/phosphate ratio (COD/P) leaching from poultry litter by optimizing process parameters such as leachate solution pH (3.46), stirring time (12.5 h), and poultry litter dosing (17.14 g/L). Subsequently, RSM was also employed to maximize P precipitation from leachate by optimizing pH (8.99), calcium (117.45 mg/L), and magnesium (167.52 mg/L) ion concentrations. The chemical precipitation process showed ∼94.16 ± 1.95% P recovery in the form of a mixture of struvite and hydroxyapatite. To achieve zero-liquid discharge (ZLD) and close the material loop, spent poultry litter was converted into iron-loaded biochar to treat the residual leachate solution (PO43− ≈ 30 ± 2.54 mg/L, COD ≈ 2560 ± 250 mg/L), achieving removal efficiencies of 82 ± 1.63% for P and 66 ± 3.01% for COD. The treated leachate was recycled and reused for the subsequent acid leaching cycle, and the P-loaded spent biochar can be repurposed as a soil fertilizer. By recovering P from poultry litter and utilizing the waste solid and liquid streams, this process closes the material loop and facilitates ZLD.