| Ammonia(NH3)is one of the most important air pollutants,which not only participate in the formation of PM2.5,but also cause eutrophication of water and soil acidification.China is one of the countries with the most ammonia emissions,and livestock production is an important source of NH3 emissions.With the analysis of NH3 emission sources in recent years,it has been found that livestock housing and manure storage processes were the main sources of NH3 in pig farming.It is of great significance to study the NH3 production mechanism and mitigation technologies in pig manure to control NH3 emissions,regulate manure management,and improve the agricultural environment.The most representative pig manure from fattening period was chosen in this research.Firstly,the urease activity in pig manure was determined using the Michaelis-Menten kinetics,and the effects of temperature,pH,and the mixing rate on urease activity in pig manure were explored.Furthermore,the characteristics of NH3 emission and urea hydrolysis process when pig manure and urine began to mix were analyzed.In order to overcome the deficiency of acidifying pig manure with sulfuric acid,it was verified that lactic acid was used to acidify pig manure.The composition in pig manure and the characteristics of NH3 emissions during acidification were analyzed and compared by setting different target pH values Morever,the distillers' grains(DG)and vinegar residue(VR)were chosen as mitigation options to mix pig manure based on the rich organic acids in DG and VR,and different mixing ratios of pig manure and acid residue were set according to lactic acid titration The effect acid residue mixed pig manure on the NH3 emission reduction and composition were further analyzed and compared.The main conclusions are as follows:Urease in pig manure showed the best activity at a substrate urea concentration of 400 mM.The maximum urea hydrolysis reaction rate and Michaelis constant were 26.9±1.2 mmol[urea]kg-1 min-1 and 99.7±3.5 mmol[urea]l-1.The optimal urease activity occurred at 35?,pH 7.0 and 821.8 rpm of stirring.The hydrolysis of urea in urine was concentrated on the initial 8 h after the mixing of feces and urine and the hydrolysis of urea was faster than the formation of TAN(TAN=NH4++NH3).However,the release of NH3 was a slow and continuous processThe lactic acid need to consume more than sulfuric acid when adicify pig manure to the same target pH values.The results indicated that the acidification of lactic acid was more efficiency than sulfuric in short term,and the NH3 mitigation can reach 83%The acidification efficiency was mainly affected by the storage time and target pH values.The content of lactic acid in adicified manure was degraded 93%within 14 days at pH 5.5.At the same time,the addition of lactic acid would increase the level of the total soluble organic carbon(TSOC),reduce the degradation rate of dry matter(DM)and protein,but had less influence on NO3-and soluble phosphorus(SP)The NH3 mitigation efficiency of distiller's grains(DG)and vinegar residue(VR)can reach 61.4%and 56.6%and it was related to addition ratio of acid residue.The adicified process of DG and VR was different from the sulfuric acid and lactic acid The pH gradually decreased and then risen,and the lowest pH value appeared on the 9th day.The degradation of lactic acid in DG mixtures was mainly concentrated in the initial 9 days and the average degradation rate was 78%.Meanwhile,the acetic acid was generated during storage,and the peak value occured on the 15th day.The addition of acid residue can make more total carbon(TC)and total carbon(TN)retained in mixtures,but it would not affect the final C/N ratio.Furthermore,the using of acid residue made the DM and OM in the mixtures more stable,the degradation rate of TSOC was slower and the content of SP was reduced.The TAN and NO3-levels in mixtures were lower than those in untreated pig manure during the whole storage process... |
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