Heavy metal sorption on struvite recovered from livestock wastewaters and release properties of granular forms.

Phosphorus recovery from wastewater is receiving more attention due to its non-renewable property. As copper (Cu) and zinc (Zn) usually occur in livestock wastewater, this study focused on metal sorption in struvite from swine wastewater and the release properties of granular struvite in solution with varying pH conditions (2, 4, 7). The results demonstrated pH values presented a slightly decreasing trend with increasing Cu/Zn ratio, and Zn exhibited higher sorption performance on struvite crystals than that of Cu. Under the high content of metals in the wastewater, Cu/Zn ratios in the wastewater contributed to varying metal binding forms and mechanisms, resulting in the difference in the leaching properties of nutrients and metal. For the granular struvite manufactured with the adhesion of alginate, the P release percentage achieved 30.3-40.5% after 96 h in the wastewater of pH 2, whereas they were only 5.63-8.92% and 1.05-1.50% in the wastewater of pH 4 and 7, respectively. Acid wastewater contributed to the release of two metals, and the release amount of Zn was higher than that of Cu, which is associated with their sorption capacity in crystals. During the latter soil leaching test of adding granular struvite, the NH-N and PO-P concentration in the effluent ranged from 0.34 to 1.26 and 0.62 to 2.56 mg/L after 96 h, respectively. However, the Cu and Zn could not be measured due to lower than the detection limit under varying treatments. Struvite might be accompanied by quicker metal leaching and slower nutrient leaching when surface sorption dominates in wastewater with lower metal concentrations.