Simultaneous capture removal of phosphate, ammonium and organic substances by MgO impregnated biochar and its potential use in swine wastewater treatment

Metal oxide-biochar composites have been used for removing pollutants from aqueous systems. In this work, optimized MgO-impregnated porous biochar was prepared using an integrated adsorption-pyrolysis method for absorption of phosphate, ammonium and organic matter (humate). Results revealed that the MgO-biochar was comprised of nano-sized MgO flakes and nanotube-like porous carbon. Mg content had significant effects on the development of the nanotube-like porous carbon structure in MgO impregnated biochar and its adsorption capacity for phosphate, ammonium and humate. The adsorption isotherms fitted by Langmuir model illustrated that the optimized adsorbent, 20% Mg-biochar, exhibited maximum adsorption capabilities of more than 398 mg/g for phosphate, 22 mg/g for ammonium, and 247 mg/g for humate, respectively. The phosphate adsorption fitted the pseudo-second-order kinetic model, while ammonium and humate adsorption were best described by the intra-particle diffusion model. The existence of Cl−, NO3−, SO42−, K+, Na+ and Ca2+ ions had no significant impacts on humate adsorption, but the presence of SO42− and Ca2+ affected the phosphate adsorption, and the presence of K+, Na+ and Ca2+ ions inhibited ammonium adsorption. Characterization of adsorbents by X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) before and after treating swine wastewater revealed that struvite crystallization, electrostatic attraction, and π–π interactions contributed to the adsorption of phosphate, ammonium and humate. The results demonstrated that the optimized MgO-biochar could be employed as an effective adsorbent for the simultaneous removal and recovery of phosphate, ammonium and organic substances from nutrient-rich livestock wastewaters.