Nitrogen Transform Process And Microbial Community Analysis Of Pig Manure Anaerobic Digestion In Thermo-,Meso-,and Psychro-State

With the continuous improvement of people’s living standards and the upgrading and optimization of China’s industrial structure,China’s livestock and poultry breeding industry is developing more and more rapidly,and the level of large-scale breeding is constantly improving.A large number of excrement produced by livestock and poultry breeding industries without effective treatment also brings a serious burden to the environment.Anaerobic digestion process can be used to recycle livestock and poultry manure and convert organics into methane fuel.Using anaerobic digestion technology to treat organic waste to the environment decontamination and recycle green energy biogas,becomes one of the ideal choices in the world.Anaerobic digestion technology is widely used in wastewater treatment.With the wide application of anaerobic digestion technology in engineering,the role of nitrogen transformation in the global biological nitrogen cycle is becoming more and more important.However,most researchers focused on how to improve the efficiency of methane production in anaerobic digestion process,but paied few attention to the nitrogen transformation microorganisms,functional genes and expression in anaerobic digestion process.For example,nitrous oxide is one of the existing forms of nitrogen,which has a stronger greenhouse effect than methane.The anaerobic digestion process will release nitrous oxide,but its release and generation process are rarely reported.In this study,the upflow carbon fiber fixed bed anaerobic reactor was used to construct a low temperature(15 ℃),medium temperature(37 ℃)and high temperature(55 ℃)anaerobic digestion system,which was operated stably for 160 days,monitored the nitrogen occurrence and gas production during operation,and extracted the total DNA of membrane sludge and fluid sludge By using 16 S PCR and Metatranscriptome,we analyzed the composition and differences of communities including nitrogen cycle related microorganisms in high,medium and low temperature,predicted nitrogen transformation related functional genes,and measured the expression of nitrogen transformation functional genes.The results are as follows:(1)In the process of building a medium and low temperature anaerobic digestion system,with the increase of the organic load of the influent,the gas production of P15(15 ℃),M37(37 ℃),T55(55 ℃)reactors gradually increased,the ammonia nitrogen concentration generally increased,the nitrate and nitrite concentration rapidly decreased in the early start-up stage,and stable in the middle and later stages,and the nitrous oxide concentration in the whole anaerobic digestion process was relatively higher For stability.Under 40000 mg / L organic load,low temperature gas production is stable at 7.5l/d,medium temperature gas production is stable at 25 L / D,and high temperature gas production is stable at 32 L / d.The concentration of low-temperature methane production is the highest,stable at about 80%,followed by hightemperature methane production,stable at about 77%,and stable at about 75% at medium temperature.In the later stage of stabilization,the ammonia nitrogen content of low temperature P15,medium temperature M37 and high temperature T55 reactors fluctuated up and down at 880 mg / L,1588 mg / L and 1871 mg / L,respectively;the nitrate was stable at about 3.3 mg / L,7.82 mg / L and 14.3 mg / L;the nitrite was stable at about 0.11 mg / L,0.43 mg / L and 1.6 mg / L.(2)Under the condition of high and medium temperature,Firmicutes are the dominant species in the reactor,and the highest relative abundance of Euryarchaeota is followed by Firmicutes at low temperature.In addition,Proteobacteria,spirochaeta and syntrophites also have high relative abundance.Temperature has the greatest influence on the methanogenic composition of the reactor microorganism,and the difference of the bacterial composition is the second.Biofilm sludge and fluid sludge formed different microbial community structure.The abundance of Archaea in low-temperature and high-temperature coated sludge was higher than that in fluid sludge,and there was no significant difference in medium temperature.(3)The number of nitrogen fixing microorganisms in the low temperature anaerobic digestion reactor is higher than that in the medium temperature(more than the number of OTUs,i.e.higher relative abundance).The main ammonia oxidizing bacteria in the anaerobic digestion reactor are AOB,belonging to gamma Proteobacteria.In addition,a small number of nitrososphaeria belonging to AOA was found.More AOB was found in the low-temperature anaerobic digestion reactor,and it was mainly distributed in the membrane sludge,which was consistent with the distribution of AOB in the medium temperature and opposite to the distribution of AOB in the high temperature.The results showed that there were no anammox microorganisms in the anaerobic digestion reactor at different temperatures.Denitrifying microorganisms are mainly distributed in the fluid sludge,and the abundance of denitrifying microorganisms in the high,medium and low temperature coated sludge is close to that in the low temperature fluid sludge,and the abundance of denitrifying microorganisms in the low temperature fluid sludge is higher,mainly belonging to gamma Proteobacteria,and the denitrifying microorganisms in the high temperature reactor mainly belong to Bacilli.(4)Nitrogen fixation is the main way of nitrogen transformation in anaerobic digestion reactor.The second is the dissimilation reduction of nitrite to ammonia,followed by denitrification.No anaerobic ammonia oxidation was found in the anaerobic digestion reactor.In this study,16 S Amplification Sequencing and Metatranscriptome were used to explain the composition of nitrogen transformation related microorganisms and the expression of functional genes in the high,medium and low temperature anaerobic digestion system,uncovered the transformation differences of nitrogen under different temperature conditions in the anaerobic digestion process,enriched the global biological nitrogen cycle process,and provided important theoretical guidance of engineering application.