Strategy of Nutrient Recovery from Domestic Wastewater Using Magnesium‐Modified Agricultural‐Waste‐Based Biochars

Abstract This work presents a reasonable strategy of optimizing the N : P molar ratio of municipal wastewater to simultaneously restore N‐NH 4 + and P‐PO 4 3− via struvite precipitation employing biochar modified with magnesium as the seeding material. The phosphate removal efficiency and ammonium removal efficiency could reach up to 71 % and 100 %, respectively. The remaining phosphate can be restored by other techniques for low phosphate concentration input, such as electrocoagulation. The XRD patterns indicate the appearance of struvite with high nutrient contents including Mg, N and P in the resulting precipitate, suggesting its potential agricultural application. The biochar from rice husk and rice straw modified with MgCl 2 solution via a simple procedure could be used as a new seeding material in struvite precipitation to simultaneously restore phosphate and ammonium from wastewater. It has been found that modifying with MgCl 2 concentration of 0.5 M and 1 M were enough to improve 14.7 % and 26.5 % of the phosphate removal efficiencies of rice straw‐based and rice husk‐based biochar, respectively. Along with the highly compatible of the post‐precipitated product with soil amendment, the magnesium modified biochars from rice husk and rice straw were highly suitable for enhancing the restoration of phosphate and ammonium via struvite precipitation.