| China is the largest producer of rice straw,although the rice straw resources are abundant,a large amount of rice straw has not been properly used or disposed,which will not only cause serious environmental pollution,but also lead to extreme waste of biological resources.With anaerobic fermentation technology as the core,methanation utilization can simultaneously realize the utilization of energy and fertilizer of rice straw,overcome the disadvantages of direct return of rice straw to the field,realize indirect return of rice straw to the field and biogas recovery,and promote material circulation,which is of great significance to ensure the sustainable and green development of agriculture.The presence of lignin and silica makes it difficult for rice straw to degrade,which makes it difficult for rice straw to be utilized by anaerobic fermentation.Therefore,in this study,rice straw and swine wastewater were used to domesticate soil microorganisms in paddy soil and the dominant microbial flora was constructed to promote rice straw hydrolysis,so that the soil enzyme activity tended to decompose straw form efficiently.The conditions of microbial hydrolysis of rice straw in domesticated paddy soil were optimized to produce and accumulate more fermentable small molecules such as TOC and VFA in the reaction system.In the optimal hydrolysis conditions,swine wastewater was added to the rice straw hydrolysis tank.After hydrolysis for a period of time,the hydrolysates were extracted in different proportions for anaerobic fermentation to produce methane,so that the rice straw hydrolysis completely,produce more small molecular organics,improve the conversion rate of rice straw and the content of methane produced by hydrolysate,and provide technical support for the subsequent industrial methane production and promote the industrial application.1)Paddy soil was domesticated under different conditions.The p H value in all groups gradually decreased in the first 15 days and then increased with the extension of domestication time.The total organic carbon content of mixed group(653.50 mg/L)was higher than that of RS group(521.50 mg/L)after 19 days.The sequence of carboxymethyl cellulose activity was as follows: mixed group(4.01 IU)> rice straw group(2.29 IU)> control group(1.03 IU)> swine wastewater group(0.87 IU).The ammonia nitrogen content showed a downward trend in all groups,which was associated with ammonia volatilization,nitrification and denitrification The cellulose/lignin ratio(5.25)and the degradation rate of lignin(51.96%)in mixed group were higher than those of other groups.According to high-throughput sequencing analysis of microorganisms in the samples,the richness and diversity of microbial communities in different treatment groups changed significantly.The addition of rice straw/swine wastewater in paddy soil could enrich degradable microorganisms due to competitive inhibition.Firmicutes(21.02%),Chloroflexi(12.48%),Proteobacteria(20.92%),and Bacteroidetes(25.78%)were the main fermentation phyla in mixed group during domestication.Lentimicrobium(1.68%),Sporobacter(0.61%),Macellabacteroides(0.68%),Ruminiclostridium?1(1.43%),Syntrophomonas(0.45%),Haliangium(1.33%),Anaerolinea(2.19%),Leptolinea(0.81%),DMER64(9.18%)and Roseimarinus(0.99%)in mixed group were mainly enriched in the process of domestication.These results indicated that the paddy soil microbial community domesticated in mixed group could degrade RS more efficiently,and mixed group was the best microbial soil for rice straw degradation.2)The conditions for producing small molecular organic matter(TOC and VFA)from rice straw hydrolyzed by soil microorganism were optimized.Through single factor and orthogonal experiment,the optimum conditions for the production of small molecular organic matter in the reaction system were as follows: reaction temperature37 ?,inoculation ratio(paddy soil: rice straw)2:1,C/N(40)and height of flooded level 8.5 cm.The confirmatory experiment showed that under the above conditions,the TOC and VFA contents in the hydrolysate of rice straw reached the highest on the third day,which were 10.45 g/L and 4.10 g/L,respectively.Meanwhile,using the hydrolysate produced under the optimal conditions of anaerobic fermentation methane production again proved that the use of rice straw hydrolysis acidification can provide sufficient substrate for the subsequent stage of methane production methane.3)The experiment of retaining hydrolysate in different proportion after adding swine wastewater in the rice straw hydrolysis tank for a certain time showed that the rice straw could be degraded completely and the yield of methane in the anaerobic fermentation of the hydrolysate could be increased by multi-stage hydrolysis treatment.The efficiency of rice stalk hydrolysis and methane production was evaluated through four hydrolysis processes of first,second,third and fourth stage hydrolysis and six different retention rates of 75%,65%,55%,45%,75-45%decreasing in turn and 45-75% increasing in turn.The results showed that: the p H of the reaction system was low(5.10)at the first stage,and gradually increased to weakly alkaline.The concentrations of small molecular organics such as TOC and VFA in primary hydrolysis were 4.77 g/L and 3.02 g/L,respectively,and the concentration of secondary hydrolysis decreased.In tertiary hydrolysis,the TOC of75%,65%,55%,45%,75-45% and 45-75% respectively decreased to 1.77,1.62,1.20,0.64,0.87 and 0.45 g/L,respectively.VFA concentration decreased to 1.04,0.45,0.15,0.08,0.26 and 0.11 g/L.Therefore,in the process of three-stage hydrolysis,the hydrolysis reaction of rice straw tends to end.In order to improve the economic efficiency of the hydrolysis,the two-stage hydrolysate of rice straw can be used in the actual operation.Meanwhile,when the retaining content is 45%,not only the TOC and VFA contents are the highest,which were 2.14 g and 7.51 g respectively,but also the methane production is the highest,which was 986.15 m L. |
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