Screening High Efficient Inoculum Strains And Studying On Fermentation Effect Of Maize Straw At Low Temperature For Methane Production

The production of plant straw in China is high for the vast crop acreage. Straw is a bio-resource with a large variety of organism, however the current utilization level is low. The main patterns of famers to deal with the straw are combustion and abandonment, it is a waste of resource and pollution to the environment. Fermenting methane can transform straw waste into clean energy, which has an important meaning to both waste treatment and energy field.Biogas has a vast potential prospect as a clean reproducible biomass energy all over the world. However, there are still some common problems during the process, such as: long fermentation period, low methane production, unstable fermentation system, these problems are more serious in low temperature fermentation. Addition of high efficiency microbial group, improve the environment can obviously enhance the performance of methane fermentation. This study use different samples from different environments to select excellent inoculum for low temperature fermentation, and optimize the ratio of total solids content and carbon nitrogen of substrate. In addition, to further intensify the fermenting effect of the strains. We analyzed the structure and composition of the strains with high throughput sequencing, result is as followed:(1) We collect sludge from Zhalong and Qunli wet land, biogas slurry of middle-temperature fermentation, cow dung as inoculum to ferment maize straw under 20°C. Through measuring the gas output, methane content, VFA and other datas, we found out that cow dung was the best inoculum: methane produced earlier than the others; peak of daily production is 310mL; total gas production is 1896 m L; peak of methane content is 40.8%, total methane production is 525 m L. Through analyzing strains after inoculation, main microorganism in the system are: Bacteroidetes, Firmicutes, Proteobacteria and Spirochaetae. Among them, Firmicutes and Bacteroidetes are predominately ruled. Among the archaea order, there are Methanosarcinales, Miscellaneous Crenarchaeotic Group(MCG)and Methanomicrobiales, Methanomicrobiales is the main strain. Among genus, there are Methanosaeta, MCG and Methanosarcina, Methanosaeta rules.(2)We optimized the condition of 20°C maize straw fermentation, during the carbon nitrogen ratio experiment, we found out that the best ratio is 25:1, under this term, peak of daily production is 123 mL, total gas production is 1168 m L and peak of methane content is 32%. Total solids content experiment showed that best solids content ratio is 10%, peak of daily gas production is 123 m L, total gas production is 1168 m L, peak of methane content is 32%. Synthesize both results, we confirmed that best condition of maize straw fermentation is solids content ratio 10%, carbon nitrogen ratio 25:1.(3)We used dung fermented sample to enrich methanogens and received stable strains after 6 generations, methane content is 45%, gas production is 46 mL. Flora analysis indicated that Firmicutes is dominant bacteria, Methanocorpusculum and Candidatus_Methanomethylophilus are the main archaea. To compare with the other strains, enriched methanogens had advance in every respect, total gas production increased 9% and total methane production increased almost 30%.