| In China,maize straws have a large production,but degree of resource utilization is low.The low gas yield of methane fermentationprocess using straw as material is a main question.This studyoptimized the nitrogen type and the nitrogen concentration to improve the gas production of straw methane fermentation.Meanwhile,the microbial diversity and abundance change analysis in fermentation samples were performed to understandthe effect ofnitrogen on the efficiency of the maize straw methane fermentation.This study added urea(organic nitrogen)and ammonium nitrate(inorganic nitrogen)into biogas fermentation system and used maize straw as feedstock.Different nitrogen concentration gradient(0 g/L,1 g/L,2 g/L,4 g/L)was set in batch anaerobic fermentation experiments,and fermentation time was 30 d.The experimental results showed that the methane-producing efficiency was thehighest when the exogenous urea was 1 g/L,and the TS methane production rate was 217.50 m L/g.Nitrogen concentration of 1 g/L with urea was used in continuous anaerobic fermentation experiment in 25 L fermentation system.The results showed that: TS methane production rate of treatment group with nitrogen were significant higherthanthat of control,and the gas production peak of treatment groupalso appeared earlier than that of control.Addiionally,nitrogen treatment can significantly increase the degradation efficiency of cellulose and hemicellulose,and degradation efficiency of lignin was not significantly different between two groups.The high-throughput sequencing technology was used to study the microbial diversity and abundance change of fermentationsamples.The results showed that nitrogen can influence the bacteria diversity significantly,but had no effect on the archaea diversity.The effect of nitrogen on the abundance of bacteria and archaea significantly.The dominant bacteria phylums(bacteria abundance more than 9%)in the samples of the fermentation period included Bacteroidetes(22.5%-43.4%),Firmicutes(18.1%-36.6%),Spirochaetes(5.2%-14.1%),Proteobacteria(2.2%-11.1%),Chloroflexi(0.7%-9.1%),etc.In the initial stage of fermentation(10d),the number of Bacteroidetes in treatment group waslower than that of contol,and Sphirochaetes number in treatment group washigher than that of control.On genus level,bacteria in each of fermentation period showed significant diversity.The dominant archaea groups(archaea abundance more than 4%)in the fermentationperiod of the samples included Methanosaeta(36.7%-68.7%),Methanoculleus(3.8%-16.2%),Methanospirillum(5.2%-9.2%),Methanobacterium(1.5%-14.3%),Methanosarcina(0.6%-4.9%).In the initial stage of fermentation(10d),Methanosaeta number in treatment decreased comparing with that of contol,and the number of Methanoculleusin treatment increased comparing with that of control.Along with the fermentation,the abundance of Methanobacteriumin control group gradually enhanced.Bacteria showed more complex diversity than archaea.In metagenomics of 1 g/L nitrongen treatment in the initial stage,the percent of bacteria was 72.37% and the percent of archaea was 18.52% in the annotated sequences,and the dominant bacterium groups mainly participate in the degradation of fat,protein,cellulose and other molecular polymer.Functional genes annotation results indicated that both hydrogenotrophic and aceticlastic pathways were in fermentation system,and hydrogenotrophic pathway wasdominated.Sphaerochaeta species were abundant,which indicated an important role in maize straw methane fermentation.To sum up,the appropriate nitrogen concentration can significantly improve the TS methane yield of maize straw fermentation;nitrogen can influence the bacteria diversity significantly,but had no effect on the archaea diversity;The study about the effect of different nitrogen type and the nitrongen concentration on maize straw biogas fermentation,can provide theoretical guidance for improving maize straw methane production efficiency and the utilization of biomass straw resource. |
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