Elucidating the function of MgO precursors on the adsorptive removal and recovery of water phosphorus

Abstract

Phosphorus (P) recovery with MgO-based adsorbents (MBA) is an effective method for water management and eutrophication prevention. However, the function of MgO precursors on the adsorptive removal and recovery of water P has not yet been sufficiently studied. Therefore, five distinct precursors, namely MgCl2·6H2O, Mg(NO3)2·6H2O, Mg(CH3COO)2·4H2O, Mg(OH)2, and Mg5(OH)2(CO3)4·xH2O, were employed to synthesize MgOs, resulting in the formation of corresponding calcination products identified as CH-MgO, NI-MgO, AC-MgO, HY-MgO, and BC-MgO, respectively. The surface morphology, Brunauer-Emmett-Teller specific surface area (SBET), total pore volume (TPV) and average pore size (APS) of the MgOs were impacted by their precursors, which affected their ability for P recovery. The flower-like BC-MgO showed the highest adsorption capacity (mg P/g) for P (426.2), followed by AC-MgO (398.1), CH-MgO (329.5), HY-MgO (296.6), and then NI-MgO (274.9). BC-MgO recovered 56.2 % of total P (TP) and 61.7 % orthophosphate (ortho-P) from livestock wastewater, and 56.3 % TP and 95.9 % ortho-P from sewage treatment effluent. P adsorption was pH dependent and positively correlated with the adsorbents SBET and TPV. Surface complexation and deposition, ligand exchange, and electrostatic attraction were the main processes involved in P adsorptive capture and its recovery. The leaching of Mg2+ into water was negligible from all studied MgOs, particularly BC-MgO and AC-MgO. The recovered P from the P-loaded BC-MgO enhanced seed germination and root growth and thus might be used in soil as an alternative P fertilizer. Based on those findings we can conclude that BC-MgO showed high potential applications for the removal and recovery of P from wastewater under wide range of water pH and therefore can be used for remediation of P-rich water. Those results are meaningful for MBA engineering application, preventing water eutrophication, producing alternative P fertilizers, and achieving sustainable development goals in future.