| Agriculture is an important part of China’s economic development,but with the development of agriculture,the pollution caused by the environment has become a long-term hidden danger.Among many agricultural environmental problems,the environmental pollution caused by livestock and poultry farming represented by pig farms should not be underestimated.The swine wastewater has high NH4+-N concentration,low C/N and high BOD5 concentration.Unreasonable discharge will trigger the epidemic of infectious diseases,as well as eutrophication of water and increase of nitrate and nitrite in water.Threatening the lives of nearby residents.At present,the commonly used treatment methods of swine wastewater are anaerobic treatment,aerobic treatment and anaerobic-aerobic combination treatment.However.the traditional treatment methods of swine wastewater have some shortcomings,such as complicated operation and management,poor stability,long residence time of wastewater,large area and so on.Because of its unique treatment characteristics.immobilized microorganism technology has become a better choice in the field of livestock and poultry wastewater treatment.In view of this,this study used immobilized microorganism technology to treat swine wastewater,and investigated the treatment performance of immobilized microorganism technology at different carrier filling rate,hydraulic retention time(HRT)and C/N operation conditions.Secondly,combined with the single factor experiment results and the basic principle of response surface analysis method,orthogonal experiments of three factors and three levels are carried out to optimize the operating conditions of the system and analyze the interaction between various factors.Then,the swine wastewater was treated at optimal conditions,and the microbial community structure in the system was analyzed to understand the system treatment characteristics and the microbial community structure changes in the system.Finally,combined with the current development and pollution status of pig industry in Yanbian area,the promotion and application of this technology in the pig industry in Yanbian area is analyzed.Through the study of this paper,the following conclusions are obtained:1)Based on the carrier filling rate,HRT and C/N as variables,the results of the treatment characteristics of the pig farm wastewater under different conditions were studied.When the carrier filling rate was 20%,the carrier microbial concentration in the system reached a maximum of 47 mg/PUFcm3.When the HRT is 24 h and the C/N is 5,the TN removal rate is optimal.2)Response surface methodology(RSM)results showed that the optimal operation conditions for TN removal from pig farm wastewater by immobilized microorganism technology were HRT 27.5 h,carrier filling rate 25%,C/N 5.48.At this time,the predicted and measured TN removal rates are 79.73%and 74.81%,respectively.There is no significant difference between the predicted and measured values.The model can effectively predict TN removal rates.Among the three factors selected in this study,the effect on TN removal rate is carrier filling rate>C/N>HRT.3)High-throughput sequencing results showed that the microbial community diversity in the system decreased with the operation of the system,while the microbial community diversity in the denitrification pool was generally higher than that in the nitrification tank.Proteobacteria and Bacteroides,Betaproteobacteria,Hydrogenophaga and Flavobacterium are the dominant phylum,class and genera of immobilized microorganisms for the treatment of swine wastewater.4)As a result of microbial community function prediction,the microbial community function in the system is mainly based on "amino acid metabolism","carbohydrate metabolism" and "energy metabolism" and other "metabolism".However,there was no significant difference in microbial community function between the five groups of samples.As the system operates,the enzymes involved in nitrogen conversion increase,and the nitrogen transformation ability of the system microbial community is strengthened.5)From 2008 to 2017,the pig industry in Yanbian area showed an upward trend,reaching the highest value in 2010 and the lowest value in nearly 10 years in 2011,then slowly increased and gradually stabilized,reaching 339.6 thousands pigs by 2017.In the past 10 years,the proportion of pig industry in livestock and poultry farming in Yanbian region decreased first and then increased.In 2017,the proportion of pig industry increased significantly,reaching 20.36%of livestock and poultry farming,which was second only to beef cattle farming as the main livestock and poultry farming species in Yanbian region.6)In 2017,the fecal and urinary production of pig industry was 341.95 kt,and the production of BODs,COD,TN and TP were 6772.98 t,7262.04 t,1379.5kt and 459.05 t,respectively.In the counties(cities)of Yanbian,the amount of excrement and various pollutants in Dunhua accounted for the most,accounting for 30.2%of the whole state;while Tumen was the least,accounting for only 5.3%of the whole state,and the difference between other counties(cities)was not significant After treatment,the concents of COD and TN concents of pig farm were 2302.79 t and 347.49 t respectively.Using immobilized microorganism technology to treat swine wastewater could significantly reduce the pollutant emissions. |
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