Mechanism and Behavior of Phosphorus Adsorption from Water by Biochar Forms Derived from Macadamia Husks

High phosphate content in water causes eutrophication, leading to many risks to the aquatic environment and human health. This study used biochar derived from macadamia husks at the pyrolysis temperatures (300, 450, and 600℃) to remove P from water. Adsorption parameters such as initial pH, biochar dosage, initial P concentration, and adsorption time when biochar was exposed to the P solution were determined. The results show that pH 4 is optimal for P removal with biochar pyrolyzed at 300 and 450°C, while pH 6 gives biochar 600°C, biochar dosage 10 g.L−1, concentration Initial P 25-200 mg.L−1 and adsorption time 40 minutes for 3 types of biochar. The maximum P adsorption capacity is 20.07, 20.03, and 20.03 mg.L−1 corresponding to 3 forms of biochar 300, 450, and 600°C. P adsorption data were consistent with the Freundlich isotherm model for all three biochar forms. The pseudo-second-order kinetic model was suitable for all three types of biochar, showing that the main adsorption mechanism is a surface chemical reaction. The study suggested that hydrogen bonding plays an important role in the adsorption of P onto biochar derived from macadamia husks. This study indicates that biochar derived from macadamia husks pyrolyzed at temperatures of 300, 450, and 600°C are all potentially effective and low-cost adsorbents for phosphate removal from water.