Enhanced removal of phosphate and ammonium by MgO-biochar composites with NH3 center dot H2O hydrolysis pretreatment

In this study, a novel MgO-biochar composite was generated for nutrient recovery from biogas slurry using magnesium chloride (MgCl2) and ammonia hydroxide (NH3 center dot H2O). Biochar properties, including pH, CEC, pHpzc, magnesium content, surface area, and total pore volume (V-total), were evaluated. Moreover, the removal of NH4+ and PO43- in both single and bi-solute system were investigated. Results indicated that NH3 center dot H2O pretreatment and MgO-coating enhanced biochar pH, CEC, and pHpzc. Additionally, there were generally higher surface area and V-total in MgAWS(550). The maximum adsorption capacities for NH4+ and PO43-, respectively, increased as WS550 (0.555 and 1.57 mg g(-1)) < MgWS550 (15.4 and 21.8 mg g(-1)) < MgAWS(550) (17.5 and 31.3 mg g(-1)). Moreover, higher removal efficiencies were achieved in the bi-solute system, and over 25% and 90% of NH4+ and PO43-, respectively, was removed from biogas slurry by MgASW(550). Mechanically, NH4+ removal was mainly attributed to ionic exchange, while PO43- adsorption on MgO-coated biochars was due to electrostatic attraction and precipitation. Furthermore, the formation of struvite (MgNH4PO4 center dot 6H(2)O) further enhanced N and P in the bi-solute system.