Ammonia and phosphorous precipitation through struvite crystallization from swine wastewater with high suspended solid

摘要

Anaerobic effluent of swine wastewater contains high concentration of suspended solid (SS), phosphate (PO4-P), ammonia nitrogen (NH4+-N), and heavy metals such as copper (Cu) and zinc (Zn), posing eutrophication and environmental risk if it was discharged into water body. Struvite crystallization is a promising way to simultaneously recover NH4+-N and PO4-P from wastewater. However, the information is very limited for recovering NH4+-N and PO4-P through struvite from wastewater containing high SS and heavy metals. In this study, the precipitation of NH4+-N and PO4-P through struvite process from real swine wastewater was investigated. The results showed that the amount of formed struvite precipitate of NH4+-N and PO4-P from swine wastewater increased as pH increased from 7.5 to 10.0. The recovery of NH4+-N and PO4-P reached the maximum of 71% and 85%, respectively, at pH 9.5. The contents of Cu and Zn in the struvite precipitates were up to 130 mg kg(-1) and 400 mg kg(-1), respectively. When polymeric aluminum (PAC) and polyferric sulfate (PFS) were separately added as coagulants, 23.9%-40.0% and 17.3%-32.4% of SS were correspondingly removed. In the following struvite crystallization process, 79% of NH4+-N and 100% of PO4-P were precipitated. The contents of Cu and Zn in struvite precipitates declined to 53 mg kg(-1) and 152 mg kg(-1), correspondingly. Combined flocculation and struvite crystallization process can effectively remove SS from the liquid, increase the recovery of NH4+-N, and decrease content of Cu and Zn in struvite precipitate, reducing the environmental risk of struvite as fertilizer.