Enhanced removal of phosphate and ammonium by MgO-biochar composites with NH3·H2O hydrolysis pretreatment
2020
Xiao, Ran | Zhang, Han | Tu, Zhineng | Li, Ronghua | Li, Songling | Xu, Zhongyang | Zhang, Zengqiang
In this study, a novel MgO-biochar composite was generated for nutrient recovery from biogas slurry using magnesium chloride (MgCl₂) and ammonia hydroxide (NH₃·H₂O). Biochar properties, including pH, CEC, pHpzc, magnesium content, surface area, and total pore volume (Vₜₒₜₐₗ), were evaluated. Moreover, the removal of NH₄⁺ and PO₄³⁻ in both single and bi-solute system were investigated. Results indicated that NH₃·H₂O pretreatment and MgO-coating enhanced biochar pH, CEC, and pHpzc. Additionally, there were generally higher surface area and Vₜₒₜₐₗ in MgAWS₅₅₀. 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) < MgAWS₅₅₀ (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 MgASW₅₅₀. 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 (MgNH₄PO₄·6H₂O) further enhanced N and P in the bi-solute system.
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