Study On Biogas Production By Anaerobic Fermentation Of Kitchen Waste And Its Microbial Community Structure

With the rapid development of the catering industry,a large number of kitchen waste has been discharged into the natural environment,causing great damage to the ecology.Using anaerobic fermentation technology to treat kitchen waste into clean energy biogas for people to use,not only avoid the pollution caused by kitchen waste,but also can alleviate the problem of energy shortage.In this study,kitchen waste was used as raw material to carry out the experimental study on biogas production by batch fermentation of kitchen waste and semi-continuous fermentation of kitchen waste,and the biogas production performance was recorded and analyzed to explore the differences in biogas production performance under different environmental conditions.In the microbial part,Mi Seq high-throughput sequencing technology was used to analyze the strains in the anaerobic fermentation system to explore the characteristics of microbial community structure under different conditions and at different fermentation periods in the anaerobic fermentation system.In this study,microbial analysis was carried out while kitchen waste was treated,which provided theoretical reference for the development and utilization of biomass energy,and played a certain guiding role in the biogas production performance of kitchen waste by anaerobic fermentation and the study of microbial community structure characteristics in the process of anaerobic fermentation.The experimental results were as follows:（1）In the batch anaerobic fermentation experiment,when the temperature to room temperature,the concentration in the fermentation was 6%under the conditions of batch fermentation experiments,biogas production performance is best,fermentation period is relatively stable,the cumulative gas production rate of14.20 L,cumulative production from 8.52 L,nissan’s largest volume of 2500 ml,at this time of Gas production rate of pool volume is 0.31 m³·m^-3·d^-1,TS gas rate is0.56 L·（g TS）^-1,VS gas rate is 0.35 L·（g VS）^-1;When the temperature is 30℃and the fermentation concentration is 6%,the batch fermentation experiment has the best biogas production performance,the fermentation cycle is relatively stable,the cumulative gas production is 19.10L,the cumulative methane production is 11.46L,the maximum daily gas production is 2600m L,the tank capacity gas production rate is 0.43 m³·m^-3·d^-1,the TS gas production rate is 0.76 L·（g TS）^-1,the VS gas production rate is 0.47 L·（g VS）^-1.When the temperature is 35℃and the fermentation concentration is 8%,the batch fermentation experiment has the best biogas production performance,the fermentation cycle is relatively stable,the cumulative gas production is 32.70L,the cumulative methane production is 19.62L,the maximum daily gas production is 7800m L,and the gas production rate of the pool capacity is 0.73 m³·m^-3·d^-1,the TS gas production rate is 0.73 L·（g TS）^-1,and the VS gas production rate is 0.54 L·（g VS）^-1.When the temperature is 40℃and the fermentation concentration is 10%,the batch fermentation experiment has the best biogas production performance,and the fermentation cycle is not stable.The cumulative gas production is 37.90L,the cumulative methane production is 22.74L,and the maximum daily gas production is 7,000 m L.At this time,the gas production rate of the tank capacity is 0.84 m³·m^-3·d^-1,the gas production rate of TS is 0.58L·（g TS）^-1,and the gas production rate of VS is 0.47 L·（g VS）^-1.When the temperature is 45℃and the fermentation concentration is 8%,the batch fermentation experiment has the best biogas production performance,and the fermentation cycle is not stable.The cumulative gas production is 43.50L,the cumulative methane production is 34.80L,and the maximum daily gas production is 9100m L.At this time,the gas production rate of the tank capacity is 0.98 m³·m^-3·d^-1,the gas production rate of TS is 0.97 L·（g TS）^-1,and the gas production rate of VS is 0.72 L·（g VS）^-1.（2）In the semi-continuous anaerobic fermentation experiment,the maximum daily gas production was 8.50 L,the maximum gas production rate（VS）of raw material was 0.35 L·（g VS）^-1,and the organic load was 3.00 g VS·L^-1·d^-1under the condition of normal temperature.Under fermentation temperature of 30℃,the maximum daily gas production is 23.50L,the maximum gas production rate（VS）of raw material is 0.98 L·（g VS）^-1,and the organic load stage is 3.00 g VS·L^-1·d^-1.Under the fermentation temperature of 35℃,the maximum gas production per day was27.00 L,and the maximum gas production rate（VS）of raw material was 1.13L·（g VS）^-1,which appeared at the stage of 2.50 g VS·L^-1·d^-1.Under the fermentation temperature of 40℃,the maximum gas production per day is 23.00L,the maximum gas production rate（VS）of raw material is 0.96 L·（g VS）^-1,and the organic load stage is 2.50 g VS·L^-1·d^-1.Under the fermentation temperature of 45℃,the maximum daily gas production was 27.00L,and the maximum gas production rate（VS）of raw material was 1.13 L·（g VS）^-1,which appeared at the stage of 3.00 g VS·L^-1·d^-1 organic load.Regardless of the temperature,the p H value generally showed a trend of first decreasing-then stabilizing-and then decreasing,basically stabilizing around 7.8～8.3.The overall methane content in the biogas produced by the fermentation system all showed an upward trend.When the fermentation system tended to be stable,the methane content in the biogas maintained between 55-65%.（3）Through Miseq high-throughput sequencing of bacterial populations,it was found that the species composition of different samples after the start of fermentation was somewhat different,but it was still less than the number of OTU before fermentation,and the abundance of species in the batch fermentation system was greater than that in the semi-continuous fermentation system.Compared with the samples before fermentation,the bacterial richness index increased,but the microbial diversity index decreased,indicating that both raw materials and temperature would affect the microbial richness in the inoculum.After the fermentation,the species richness and species diversity of the fermentation system decreased,which indicated that the species diversity among the samples after the fermentation was less than that in the peak period of gas production.For anaerobic fermentation system composition and relative abundance of species analysis,on the level of the door,when the gas peak,dominant species of batch fermentation system mainly for the Firmicutes,Bacteroidetes,Synergistetes to each other,semicontinuous fermentation system in addition to this,the advantages of species and Thermotogae,Proteobacteria,Cloacimonetes,etc.At the order level,the dominant species in the batch fermentation system are mainly Clostridiales,Bacteroidales,Synergistales,etc.And the dominant population in the semi-continuous fermentation system,such as Petrotogales,Kosmotogales,Sphingobacteriales,etc.Which are not dominant in the batch fermentation system,are relatively high in abundance in the semi-continuous fermentation system.In division level,in the fermentation system have Porphyromonadaceae,Clostridiaceae＿1,Synergistaceae,Rikenellaceae for anaerobic fermentation system such as high relative abundance of flora,but in batch and semi-continuous system content is different,the advantage bacteria population at different temperatures is endless also and same,and in the same conditions of different fermentation periods,species,community structure also has very big difference,and the change of the present different characteristics.（4）By Miseq high-throughput sequencing of the archaea populations,it was found that the species diversity in the semi-continuous fermentation system decreased rapidly after the end of fermentation,while the species diversity in the batch fermentation system also decreased,but it still maintained to a certain extent.Compared with the peak of gas production,all kinds of indexes at this time decreased,and the decline rate of semi-continuous fermentation indexes was much greater than that of batch fermentation samples.Compared with the species composition in the peak period of anaerobic fermentation,the species composition after the end of anaerobic fermentation changed somewhat and generally showed a downward trend.In batch fermentation,when anaerobic fermentation in gas production peak,Methanosarcinaceae of the relative abundance of species in three different temperature of samples were 51.90%,79.43%and 81.39%,and when at the end of the fermentation,Methanosarcinaceae eight fold aureus the relative abundance of species in the three samples was 78.80%,58.68%and 46.69%,the fermentation in batch fermentation temperature is higher,At the end of fermentation,the proportion of Methanosarcinaceae was lower,and the relative abundance of Methanosaetaceae was increased to 25.50%and 45.51%at other temperature conditions,except that the relative abundance of Methanosaetaceae decreased to8.47%at 30℃.In semicontinuous fermentation,Methanosaetaceae the relative abundance of the mane is higher,in the dominant population,compared with gas peak in three and a half continuous fermentation samples were 33.23%,26.84%,45.71%,the relative abundance of,when the end of the fermentation,relative abundance into 50.86%,85.54%and 7.78%,and The Times of dominant population Methanosarcinaceae the relative abundance of the eight fold aureus into 12.64%,8.43%and 81.45%,in addition to the dominant population,The relative abundance of non-dominant populations decreased with the end of batch fermentation,while the relative abundance of non-dominant populations increased with the end of semi-continuous fermentation.（5）Through comprehensive analysis under different conditions of anaerobic fermentation system in different fermentation stages of microbial community structure change,can be concluded that microbial anaerobic fermentation and anaerobic fermentation system,the mutual relations between different microbial community structure caused the anaerobic fermentation of different gas effect,even the same kind of microorganism,in different fermentation conditions,or the batch fermentation and between continuous fermentation,or is it the same fermentation under the condition of the relative abundance of the different fermentation periods are not the same,that different environmental conditions to choose different microorganisms as the dominant population,on the other hand,different dominant population and caused the biogas production effect in different environments.