Investigation On The Recovery Of Nitrogen And Phosphorus From Swine Wastewater Through Struvite Process And Its Biosafty

Swine wastewater contains not only high concentrations of suspended matter（SS）and organic matter,but also high concentration of nitrogen and phosphorus and other nutrients.Cu²⁺,Zn²⁺and antibiotics are often used in livestock and poultry breeding.Most of them are excreted in the body,which may have adverse effects on biodiversity and ecological environment.Magnesium ammonium phosphate（struvite）precipitation could recover nitrogen and phosphorus at the same time,but the influence of SS on struvite precipitation and the deposition of the heavy metal and antibiotic resistance genes in the process of struvite precipitation are unclear.In this paper,the influence of high SS on the crystallization process of struvite and the deposition of the heavy metal and antibiotic resistance genes（ARGs）in struvite were investigated.The specific conclusions are listed as follows:（1）The effects of pH and N:P:Mg on the recovery of nitrogen and phosphorus in wastewater from high-strength SS aquaculture were studied.The results showed that the removal of pollutants increased with the increase of pH and the molar ratio of P:Mg to N.The recovery of NH₄⁺-N and PO₄^3--P when the pH increased from 7.5 to 10.0,which were up to 71%and 85%respectively.High SS has a certain inhibitory effect on the recovery of nitrogen and phosphorus from swine wastewater by struvite precipitation.The flocculation pretreatment of swine wastewater can increase the recovery rate ofNH₄⁺-N by 6%,the removal rate of SS by 20%and the removal rate of TCOD by10%.（2）The deposition of metal ions during the struvite crystallization was investigated.The results showed that the content of metal ions in the struvite precipitates under different pH and N:P:Mg changes greatly.At pH10,the content of Na,K,and Ca suddenly increases to 1³ times than at pH 9.5.The highest concentrations of Cu and Zn reached 130 mg kg^-1 and 400 mg kg^-1,respectively.The effect of flocculation on the removal of metal ions is poor.NaOH as a coagulant can reduce the metal ion content in struvite precipitates by 1 times.The minimum content of Cu and Zn can be reduced to53 mg kg^-1 and 185 mg kg^-1.（3）The deposition of ARGsduring the struvite crystallization was investigated.The results showed that the concentration of ARGs in struvite precipitates increased with the increase of pH,and the content of target ARGs in struvite precipitates increased 5¹0times compared with the concentration in swine wastewater.The concentration of ARGs in struvite precipitates increased by 2³ orders of magnitude,which ranged from1.0E+07copies g^-1 to 1.0E+12 copies g^-1.When the molar ratio of P:Mg to N increased from 1:0.7:0.7 to 1:1.1:1.1,the ARGs content in the struvite precipitate increased by0.5¹ orders of magnitude.PAC flocculation can reduce the concentration of tetW and sulI in wastewater by 1² orders of magnitude.