Study On Acid Production And Anaerobic Fermentation Performance Of Rice Straw Degraded By Composite Microbial System

Due to the complex chemical structure of rice straw,the hydrolysis acidification efficiency of rice straw is very low,which becomes the rate-limiting step of anaerobic fermentation.In recent years,studies have focused on using composite bacteria to pretreat rice straw for anaerobic fermentation.However,composite bacteria contain a wide variety of microorganisms,what’s more,their metabolic mechanism is not clear.Polyhydrolase secreted will produce multiple acidic products,including the acetic acid,which is beneficial to anaerobic fermentation,and on the other side,propionic acid,which inhibits fermentation.Composite strains in this article,through the pretreatment of rice straw,the purpose of it was to explore the degradation effect and acid production effect of rice straw by composite strains,and analyze the advantages of microbial flora in the process of fermentation bacteria and its related functions,in addition,the research on composite degradation strains of rice straw to produce acid half-and-half for the influence of two phase anaerobic fermentation,and on this basis,self-made sludge ceramsite biofilm with dehydrated sludge,clay and straw powder as raw materials was added in the anaerobic fermentation to improve the density of microorganisms,and the influence of ceramsite biofilm on anaerobic fermentation was verified,and the following conclusions were drawn:(1)The results showed that after 12 days of fermentation,the degradation rate of rice straw reached 89.02%,what’s more,cellulose and hemicellulose reached 80.51%and 88.73% respectively,and the degradation rate of lignin,the most difficult to degrade,also reached 62.68%.During this fermentation,the contents of acetic acid and butyric acid as the main acidizing products accounted for 48.34% and 33.19% of the total Volatile Fatty Acid(VFAs),respectively,the maximum contents of acetic acid and butyric acid were 2 278.36 mg/L and 1 485.89 mg/L,respectively.(2)16S rRNA sequencing technology and metagenomic sequencing technology were used to analyze the acid-producing fermentation process of rice straws pretreated by composite strains,and the results showed that: The composite strains were mainly composed of Cellulosilyticum,Prepotella,Pseudomona,Mobilitalea,Lysinibacillus,Clostridium and Oscillibacter,and their relative contributions to carbon metabolism were more than 45%.Among them,the relative contributions of Prepotella and Cellulosilyticum to fructose,mannose-metabolism and pentose transformation were the largest,reaching 20.90% and 11.98%.Pseudomona had the largest relative contribution to lignin degradation,which reached 7.5%.(3)The results of rice straw degraded by composite strains showed that the daily gas production was increased by 11.34%,and the methane contentand was 25.24%compared with the control,the cumulative methane production was 278.39 m L·g-1 vs.In order to fit the cumulative methane production,a modified Gompertz model was used,and it was found that the cumulative methane production in the experimental group was increased by 51.35% compared with the control group,and the methane production delay period was 4.67 d earlier than that in the control group.(4)According to the Riley three-phase diagram for the range of raw material chemical composition of ceramsite,the raw material composition of homemade sludge ceramsite: the dehydrated sludge content is 40%,the clay content is 50%,the rice straw powder content is 10%.The properties of the sludge ceramsite prepared according to this ratio,the single compressive strength of sludge ceramsite is 1.77 MPa,the specific surface area is 7.89×104 cm2/g,the acid resistance mass loss rate is 1.013%,the alkali resistance mass loss rate is 0.618%.(5)The self-made sludge ceramsite was added into the anaerobic fermentation with the acid solution produced by the composite bacteria degradation of rice straw.The results showed that the daily gas production and methane content were increased by9.36% and 4.27%,respectively,compared with the control,and the cumulative methane production was 288.91 m L·g-1 vs.The modified Gompertz model was used to fit the cumulative methane production,and it was found that the cumulative methane production in the experimental group was 3.07% higher than that in the control group,and the methane production delay period was 0.49 d earlier than that in the control group.