Study On Biological Mechanism Of Nitrogen Transformation And Nitrogen Gas Release From Sewage Sludge Composting Regulated By Carbon

Sewage sludge is an inevitable by-product in the process of sewage treatment of urban sewage treatment plants.With the acceleration of urbanization construction and the improvement of sewage treatment system,sewage sludge yield is increasing year by year,and the secondary pollution problem caused by it is also increasing protruding.Aerobic compost is one of the mainstream technologies in the sewage sludge treatment industry at home and abroad because of its easy control and low cost.However,the nitrogen loss caused by ammonia and nitrous oxide emissions and environmental pollution are important issues that the process has not been solved for a long time in practical applications.Therefore,this study reduced the nitrogen loss by adding carbon source to control the nitrogen conversion process in compost,analyzed the relationship between the application of carbon source to control sewage sludge compost and nitrogen biotransformation,and investigated the effect of carbon source on ammonia assimilation,nitrification and denitrification,explored the mutual interaction between source intensification and the functional microbial population and related functional genes in the composting systems.And improved the carbon source control sewage sludge composting process.In this paper,the influence of carbon source regulation on chemical and chemical indexes and nitrogen conversion in sludge composting process is analyzed from the basis of the types of carbon source and the proportion of added carbon source.The breeding and function of ammonia assimilation microorganism were studied.The results showed that easily degradable carbon sources significantly promoted the degradation rate of compost organic matter.while the control of sucrose in nitrogen loss was the best,only 15.87%.The addition of sucrose reduces the concentration of NH₄⁺-N,delays the occurrence of NH₄⁺-N concentration peak,and the addition of sucrose reduces the ammonia volatilization.In addition,the addition of sucrose can promote the growth and reproduction of ammonia assimilation bacteria.At the same time,the relative abundance of two genus Bacillus and Wautersiella was improved.It was found that the addition of sucrose can promote the metabolism of carbon source in compost,accelerate the circulation rate of tricarboxylic acid,increase the content of?-ketoglutaric acid in the compost,and also increase the activity of glutamate dehydrogenaseGDH),the glutamine synthetase?GS?and glutamate synthetase?GOGAT?,thereby improving the ammonia assimilation ability of microorganisms.The study also obtained a group of ammonia assimilation function bacteria by plate separation screening and random compound selection.The bacteria agent can accelerate the composting process,improve the organic matter degradation rate and dehydrogenase activity,and also improve the ammonia assimilation in the compost.However,it may be that the bacteria agent accelerates the ammoniation in the initial stage of composting,thus weakening the ability of the bacteria agent to inhibit ammonia volatilization.The effects of carbon regulation on nitrification and denitrification and N₂O release in composting system were investigated by analyzing the variation of community structure and related functional gene abundance of nitrifying and denitrifying microorganisms.The addition of sucrose significantly reduced the volatilisation of N₂O in the compost.At the same time,the number of nitrifying bacteria in the sucrose group was more than that of treatment group during the entire composting process.The two treated denitrifying bacteria did not differ significantly in the first ten days of composting.At the same time,the addition of sucrose increased the abundance of amoA gene,reduced the abundance of hao gene,thereby limiting the conversion rate of NH₂OH-N to NO₂^--N,and increased the abundance of nxrA gene,thereby improving enzyme activity of nitrite redox and promoteed the conversion of NO₂^--N to NO₃^--N.The abundances of denitrification genes narG,nirS,nirK and norB in the sucrose treatment were lower than the control treatment.In addition,the spearman correlation analysis showed that the number of nitrifying bacteria was significantly positively correlated with NO₃^--N and nxrA.The addition of sucrose promoted the growth and reproduction of nitrifying bacteria,and the nitrification product NO₃^--N and the nitrite oxidoreductase gene nxrA abundance also showed a consistent rule,while the concentration of NO₂^--N and the amount of N₂O volatilization,narG,nirS and norB were positively correlated,indicating that denitrification in the compost is the main path of N₂O generated.In order to improve the practicability of carbon source enhanced sludge composting,and considering the biological effectiveness of carbon source and the feasibility of composting operation,this paper selected spent mushroom substrate?SMS?and molasses as carbon source to carry out technology research.The resluts showed that the addition of SMS and molasses could significantly improved the degradation rate of organic matter,especially in the mesophilic phase and thermophilic phase of composting.According to the maturity index,it could be found that the addition of SMS and molasses significantly accelerated the composting process and improved the maturity of compost products.The ammonia volatilization amount was reduced by 33.1%to 37.3%by the addition of SMS and molasses.In addition,the effect of joint addition of SMS and molasses on the control of N₂O volatilization was more effective.The cumulative volatilization of N₂O was only 17.8%²5.4%of the control treatment,and the nitrogen loss of SMS and molasses treatment decreased by 42.6%⁴7.6%.It indicated that the joint addition of SMS and molasses can effectively control the nitrogen-containing gas volatilization and nitrogen loss in composting of sewage sludge.