| The development of livestock and poultry industry in China ranks among the top in the world.Under the dual role of national support and social demand,the livestock and poultry industry shows a rapid and orderly development trend.However,the environmental pollution caused by improper disposal of livestock and poultry excrement is becoming more and more serious.Rational use of livestock manure resources can effectively reduce the use of fertilizer,reduce environmental pollution,and achieve the goal of human sustainable development.In this paper,the five most common kinds of livestock and poultry excrement were selected as the research object,aiming at a series of problems such as high harmfulness and high difficulty in resource recovery,the basic physical and chemical properties and characteristics were compared and analyzed,and the difficulties in treatment and utilization were discussed.On this basis,the new treatment methods of pig manure and duck manure were studied by Magnesium Ammonium Phosphate（MAP）precipitation technology,and the treatment process was optimized under the premise of ensuring the removal of nitrogen and phosphorus from fecal wastewater,a feasible solid-liquid separation technology of fecal wastewater was established,which improved the treatment effect.Using fresh livestock and poultry excrement as experimental material,the basic physical and chemical properties,such as p H,moisture content and ash content,and the water characteristics,the solid characteristics and the nitrogen and phosphorus content were investigated by different methods.The results show that dewatering of cow manure and sheep manure is of high energy consumption and difficulty,but the soluble nitrogen and phosphorus content is low,desiccant treatment should be considered.Pig and duck manure have wide particle size distribution and high nitrogen and phosphorus content,which can be solid-liquid separation.The ash content in chicken manure is high,and the undigested food residues are rich in large particles,which should be treated as feedstuffs.Based on these characteristics,the process of inorganic acid mineralization+MAP precipitation+lime milk coagulation was used to treat pig manure wastewater.The results show that the optimal treatment conditions are inorganic acid mineralization time of 2 h,MAP precipitation p H of 9.0,and the dosage of phosphoric acid,magnesium salt and lime milk are3.5,9 and 16 g/kg,respectively.Under this conditions,the removal rates of NH4+-N,TN,PO43--P,TP and turbidity are 75.60%,44.84%,95.52%,92.39%and 95.40%,respectively.Basis on the pig manure treatment process,two magnesium sources were selected for MAP precipitation treatment of duck manure wastewater,and the process optimization and economic analysis were carried out.The results show that the optimum process conditions of MAP precipitation with magnesium chloride as magnesium source are p H=9.5,the dosage Mg:P molar ratio is 1.5:1,and the TN and TP removal rates of wastewater are 36.34%and 89.29%,respectively.The TN and TP removal rates of the wastewater are 51.49%and 83.37%,respectively,in the MAP precipitation method with heavy magnesium oxide as the magnesium source at p H=9.5.According to the economic analysis,the alkali consumption of magnesium chloride treatment is high and the cost is high.Heavy magnesium oxide treatment cost is low,but the operation is difficult and the agent is more waste.The results show that the composition of livestock and poultry excrement is special and the physical and chemical properties are quite different,which has potential hazard and recovery value.MAP precipitation technology can remove nitrogen and phosphorus pollutants from fecal wastewater,and has obtain good application effects in the solid-liquid separation process of pig manure and duck manure.This research provides theoretical basis and technical support for the resource treatment of livestock and poultry excrement and the wastewater MAP precipitation recovery technology. |
