Forward osmosis promoted in-situ formation of struvite with simultaneous water recovery from digested swine wastewater

Livestock wastewater contains a large amount of nutrients that are available for recovery. In this study, a proof of concept process based on forward osmosis (FO) was proposed and investigated for in situ formation of struvite from digested swine wastewater. This FO system took advantage of a drawback – reverse solute flux (RSF) and used the reverse-fluxed Mg2+ for struvite precipitation, thereby accomplishing recovery of both water and nutrient. With 0.5 M MgCl2 as a draw solution, high-purity struvite formed spontaneously in the feed solution and the water flux through the FO membrane reached 3.12 LMH. The precipitated struvite was characterized and exhibited a similar composition to that of commercial struvite. The FO system achieve >50% water recovery and >93% ammonium nitrogen removal from the digested swine wastewater; in particular, it obtained >99% phosphate recovery, much higher than 60.7% removal via direct MgCl2 addition (without FO treatment). The recovered products (both struvite and water) could potentially generate a value of 1.35 $ m−3. The results of this study have demonstrated the feasibility of nutrient recovery from livestock wastewater promoted by FO treatment.