Phosphorus removal mechanism from liquid phase using digestatederived biochar

Phosphorus (P) pollution and minimizing its environmental impact on the water bodies are becoming public concerns. The biochar derived from the digestate of food waste (BC-DFW) possesses a porous structure, abundant metals, and other beneficial properties, making it a promising candidate for P removal. This study investigated the P removal efficiency and mechanism using various particle sizes of BC-DFW. Results indicated that the BC-DFW with a particle size of 40-80 mesh achieved over 90% P removal efficiency under an initial P concentration of 20 mg L-1. The pseudo-second-order kinetic model was more suitable for describing the P adsorption process by BC-DFW, compared to the pseudo-first-order kinetic model, suggesting that chemical adsorption may be the dominant mechanism for P removal. The various metals (i.e., Ca and Fe) presented in BC-DFW could react with H2PO4- , HPO42-, and PO4 3- to form chemical precipitations (i.e., Ca5(PO4)3OH). Additionally, the porous structure and functional groups of BC-DFW could also facilitate P adsorption through physical adsorption, functional group reactions, and ligand exchange. These findings provide compelling evidence for the effectiveness of BC-DFW as a potential adsorbent for P removal.