Poultry manure conversion into eco-friendly materials: synthesis of Mg-/Al-based biochars, characterization and application for phosphorus recovery from aqueous solutions

This work explores the conversion of raw poultry manure (RPM) into tailor-made biochars for an efficient phosphorus (P) recovery from aqueous solutions. To this end, three RPM-functionalized biochars with Mg (RPM-B-Mg), Al (RPM-B-Al), and Mg/Al-layered double hydroxides (RPM-B-Mg/Al-LDHs) were synthetized, deeply characterized, and then tested for P recovery under various experimental conditions. Biochar characterization showed that RPM-B-Mg/Al-LDHs had enhanced texture and surface chemistry linked to the formation/deposition of Mg- and Al-based nanoparticles. In addition, this biochar exhibited the highest P recovery rate from effluents (78 mg g⁻¹). This recovery process seems to occur heterogeneously on multilayers through electrostatic interactions, ligand exchange, surface precipitation as AlPO₄ and Mg₃(PO₄)₂, and complexation. Phosphorus desorption from these P-loaded biochars was significantly dependent on the pH of eluent solutions with the highest desorption yield observed at an initial pH of 9.0 (88%). All these findings indicate that the use of Mg/Al-LDHs-loaded poultry manure biochar can be considered a sustainable material for P recovery from aqueous solutions. Furthermore, the P-loaded biochar could be reused in agriculture as a low-cost biofertilizer in P-depleted soils.