Phosphorus recovery from swine wastewater by struvite precipitation: compositions and heavy metals in the precipitates

Recovering phosphate and ammonium as struvite from swine wastewater has gained importance as a means of relieving water eutrophication and the scarcity of phosphorous rock resources. Recently, it has been generally accepted that the quality of recovered products can facilitate the market development of nutrient recovery. In this work, the compositions and heavy metals in the recovered products of struvite recovered from swine wastewater were investigated by dosing industrial-grade (IG) MgO and Mg(OH)(2) as the low-cost magnesium sources. Results revealed that struvite (34.4-40.4% weight ratio) was the dominant mineral in the precipitates, mixing up with amorphous calcium phosphate (7.8-9.5%) and residual IG-MgO or IG-Mg(OH)(2) (9.0-19.3%). The inactive components of organic matter and refractory materials occupied significant parts of the precipitates, with their levels of 14.1-20.6% and 18.9-24.4%, respectively. It was noticeable that Cu and Zn in the collected solids were above the legal limits, suggesting that pretreatment methods were necessary to remove heavy metals from swine wastewater before struvite recovery.