Phosphate recovery from liquid fraction of anaerobic digestate using four slow pyrolyzed biochars: Dynamics of adsorption, desorption and regeneration.

Four slow pyrolyzed biochars produced from wood (WDB), corncobs (CCB), rice husks (RHB) and sawdust (SDB) were evaluated for adsorption, desorption and regeneration of phosphate (PO43--P) from anaerobically digested liquid swine manure. The PO43--P adsorption capacity increased followed by initial concentrations increasing. Maximum PO43--P adsorptions at initial 150 mg/L of PO43--P (highest load) were average of 7.67, 6.43, 5.73 and 5.41 mg/g for WDB, CCB, RHB and SDB, respectively. Pseudo second order kinetics model could best fit PO43--P adsorption, which indicated the chemisorption via precipitation was the main mechanism for PO43--P removal. The sorption process was reversible and the adsorbed PO43--P could be desorbed in both neutral (57-78%) and acidic solution environments (75-88%) for all biochars. Meanwhile, regenerated biochar could re-adsorb up to 5.62 mg/g at the highest initial PO43--P of 150 mg/L. The present finding implied biochar could be effectively used to recover PO43--P from anaerobic digestate.