Research On Pretreatment Of Livestock And Poultry Manure Fermenting Slurry And Phosphorus Recovery By Magnesium Ammonium Phosphate Crystallization

With fast intensive and large-scale development of livestock and poultrybreeding in China, environmental pollution became increasingly serious. Anaerobicfermentation was widely employed in aquaculture wastewater treatment, yet highconcentration of organic matter, nitrogen（N） and phosphorus（P） were contained inlivestock and poultry manure by anaerobic fermentation.Phosphorus is important influencing factor of eutrophication and non-renewableresources. Recovering nitrogen and phosphorus from livestock and poultry manurefermenting slurry by magnesium ammonium phosphate crystallization is of greatsignificance to lower costs of comprehensive treatment for aquaculture wastewater,realize sewage resource and sustainable use of nutrients.In addition to high concentrations of phosphorus, large number of suspendedmatter（SS） was contained in livestock and poultry manure fermenting slurry thatwould affect magnesium ammonium phosphate crystallization reaction and purity ofcrystallized product. The crystallized product was integrated with SS and hard toseparate. As a result, in order to recover phosphor, SS must be removed bypretreatment of fermenting slurry.Biological anaerobic treatment, chemical flocculation and physical treatmentwere employed to pretreat fermenting slurry in this study. Then for the method thatremoval efficient was better, the water sample after pretreatment was processed bymagnesium ammonium phosphate crystallization to recover phosphor. The influenceof pH value and Mg:P molar ratio on magnesium ammonium phosphate reaction wasstudied, and scanning electron microscope （SEM） and X-ray diffraction （XRD） wereemployed to detect and analyze the crystallized product. The study would exploresimple and easy technological approaches for the treatment of aquaculture wastewater and resource of nutrients.Results of study showed that cationic polyacrylamide（CPAM） was more efficientfor SS removal than other pretreatment. At SS of13500mg/L, a0.2%CPAM dosageof210mL that the actual dosage was1.02g/L could lower the SS to148mg/L,reaching a removal efficiency of98.9%.For the raw fermenting slurry, concentration of PO₄^3--P was72.5mg/L, at Mg:Pmolar ratio of1:1and the pH value9.5, phosphate removal efficiency was48.3%after reaction. Magnesium ammonium phosphate reaction was not complete which isdue to the high concentration of SS.After flocculating pretreatment, concentration of PO₄^3--P was about35mg/L,and magnesium ammonium phosphate crystallization process was used to recoverphosphorus. It showed that at Mg:P molar ratio of1:1, the optimum pH value was9.5,at which the phosphate removal efficiency was78%; while at Mg:P molar ratios of1.5:1and2:1, the optimum pH value was10.0, at which the phosphate removalefficiency was86.6%and91.9%. SEM and XRD were employed to detect andanalyze the crystallized product, and it showed that the product was magnesiumammonium phosphate.