Phosphorus recovery using magnesium-enriched biochar and its potential use as fertilizer

Phosphorus (P) recovery from wastewater using biochar is an alternative to P recycle and reuse. However, the impregnation of cations for biochar production is needed to enhance P removal. We aimed at studying the P adsorption and release capacity of biochar enriched with magnesium (Mg2+) and its potential use as fertilizer. Biochars were produced from poultry litter (PLB), pig manure (PMB), and sewage sludge (SSB) impregnated with MgCl2. Characterization comprised pH, Electrical conductivity, total nutrient content, moisture and ash contents, FTIR, XRD, Raman, and SEM-EDX. Phosphorus adsorption isotherms by biochars were obtained and P desorption was also studied. A pot experiment with maize in an Oxisol was performed with the P-loaded biochars, triple superphosphate – TSP (positive control) and no P application (negative control). PMB showed the highest P adsorption (68.0 mg g−1). The main mechanisms of P removal were through precipitation with cations, ligand exchange reactions and electrostatic attraction on the biochar surface. The P-loaded biochars promoted plant growth and accumulation of P in maize, which was similar or greater than TSP. In conclusion, Mg-impregnated biochar is a sustainable option to add value to organic residues and to recycle P to be reused as enhanced efficiency fertilizer.