Application Of A Novel Biochar Adsorbent And Membrane To The Selective Separation Of Phosphate From Phosphate-Rich Wastewaters

A novel biochar from Rosmarinus officinalis leaves (BRM) was employed for phosphate removal and recovery and compared with ZnO as a reference. Further, an adsorptive mixed matrix membrane suitable for practical adsorption applications in industry was fabricated by incorporating BRM particles in a polymeric matrix (PVC-BRM). The adsorption capacity of the BRM was tested by isotherm and kinetic experiments, and the adsorption properties of the membranes were evaluated by filtration experiments in a cross-flow system. Both BRM and PVC-BRM were characterized by analyzing their morphology and composition. The maximum adsorption capacity of BRM was 78.24 mg/g, and the adsorption of phosphate was endothermic and obeyed the Langmuir and Freundlich isotherms, indicating that multiple mechanisms are involved in the adsorption. BRM and PVC-BRM exhibited high removal efficiencies toward phosphate in a wide range of single and multi-component solutions. In a multi-component system, phosphate displayed preferential adsorption for BRM; in PVC-BRM, however, phosphate selectivity decreased. The adsorption of phosphate was pH-dependent and was enhanced in acidic conditions. The adsorption capacity increased with higher initial phosphate concentration for BRM and PVC-BRM, although removal efficiency decreased. Desorption efficiency was low in both BRM and PVC-BRM; however, 75% regeneration was achieved by NaOH in BRM. The membrane showed higher reusability than BRM. Adsorption mechanism studies revealed that the removal of phosphate was associated with ion exchange, electrostatic interaction, hydrogen bonding, ligand exchange, and precipitation with metal oxides and hydroxides. Besides, BRM exhibits excellent selective separation of phosphate from different wastewaters and agriculture runoff as secondary resources.