| In order to improve the biogas production performance in anaerobic digestion of cattle manure in cold regions.This study carried out the sequencing batch anaerobic digestion experiments with cattle manure at medium?37??and low temperatures?15??20?and25??for 50 days.The effects of temperature on the changes of routine parameters in biogas daily yield,biogas accumulation,volatile fatty acids concentration,and COD concentration were studied.In addition,the changes of different enzyme activities?cellulase,hemicellulase,protease and amylase?and microbial community structure characteristics during the whole anaerobic digestion process under different temperature conditions were emphatically analyzed,and comparing the differences in enzyme activity and microbial community structure under different temperatures.This study can provide a reasonable data reference and an effective biological basis to improve biogas production efficiency and stabilize operations for the biogas project in the cold regions of northern China.The results and conclusions are as follows:Firstly,by comparing the changes in biogas production characteristics during the anaerobic digestion of cattle manure at medium and low temperature,the anaerobic digestion of cattle manure at 37°C experimental group had better gas production performance,and the maximum methane yield was on the 6th day,which was 19.18 m L·g VS-1,the cumulative gas production is 403.64 m L·g VS-1,The experimental group at 15°C,20°C,and 25°C reachd the maximum daily yields of methane on days 37th,25th,and 18th,respectively,which was6.92 m L·g VS-1,9.96 m L·g VS-1,and 14.40 m L·g VS-1.And the cumulative methane production was 176.66 m L·g VS-1,234.95 m L·g VS-1,270.31 m L·g VS-1,respectively.The concentration of volatile fatty acids in anaerobic digestion experiment groups at different temperatures increased first and then decreased,and finally stabilized,and the anaerobic digestion system of experimental group at 37°C showed the best p H stability.Then,the COD concentration in the digestive juices with different temperatures gradually increased with the increase of different kinds of enzyme activities.The maximum concentrations of COD in the experimental group were 14073.29 mg·L-1,12835.31 mg·L-1,13917.66 mg·L-1 and 14016.70 mg·L-1 at 15°C,20°C,25°C and 37°C,respectively.In the appropriate temperature range,the higher the temperature,the stronger the enzyme activity,and the maximum enzyme activities of different types are 242.81 U·m L-1,348.85 U·m L-1,164.31 U·m L-1 and 328.73 U·m L-1.At the same time,the results of 16s-r RNA sequencing of anaerobic digestion system of cattle manure at different temperatures are as follows,The species richness index,Chao1index,shannon index and simpson index of cattle manure anaerobic digestion experiment in the 37°C experimental group were the largest.The dominant bacteria at the gate level in anaerobic digestion of cattle manure at different temperatures were Bacteroidetes,Proteobacteria,The sub-dominant bacteria is the Firmicutes and the Euryarchaeota.The dominant flora at the genus level includes Vadin BC27-wastewater-sludge-group and Methanosaeta.The dominant methanogenic archaea of the methanogenic phase is Methanosateta,Methanospirillum and Methanoculleus.Finally,a first hydrolysis kinetic model was used to linearly fit the anaerobic digestion of cattle manure at different temperatures.It was found that as the temperature decreased,the hydrolysis rate constant k gradually decreased,and the 37?experimental group showed optimal methanogenesis performance.The Gompertz equation and the Logistic equation were used to non-linearly fit the relationship between the cumulative production and time of anaerobic digestion of cattle manure at different temperatures,and the fitted curves R2were greater than 0.99.The Gompertz equation and Logistic equation can better fit the sequencing batch anaerobic digestion process of cattle manure at different temperatures. |
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