Study On Hydrogen Production System And Microbial Community Structure By Anaerobic Fermentation

Economic development,energy and the environment are common concern to the whole world and all mankind,and that are also important issue in China's social and economic devel-opment.Bioenergy,as a renewable and environment friendly energy source,has unparalleled superiority.Bio-hydrogen production technology from wastewater has become one of the re-search hotspots in environmental biotechnology.Microbial community structure of Activated sludge has a decisive influence on hydrogen production efficiency.Therefore,using modern molecular biology methods to elucidate the relationship between microbial community struc-ture and hydrogen production efficiency,can be useful for achieving targeted construction and optimization of high-efficiency hydrogen-producing communities.The research on the ethanol-type fermentation microbial community is still in the initial stage.This experiment used the CSTR reactor and the IC reactor as the acid-producing phase,and the hydrogen-producing rate and the wastewater treatment performance of the system are investigated using the molasses wastewater and the beer wastewater as the substrate.the com-ponents of the liquid-phase end products of each phase can be used to investigate the physio-logical and metabolic characteristics of the hydrogen-producing fermentation system.The Study on the physiological and metabolic characteristics of the hydrogen-producing fermenta-tion system,we can further understand and summarize the system response parameters,the ac-tion law between the community and the fermentation type contribute to the succession of the target top-level communities.The operating conditions of the corresponding system are con-trolled in order to obtain the maximum yield of the target product and the energy yield,which can further provide the basis for further exploring the productivity potential of the anaerobic digestion system.In the study of optimum hydraulic retention time?HRT?of CSTR hydrogen production system,the maximum hydrogen production rate was 1.42 L/L/d,and the maximum COD re-moval rate was 38.67%under the HRT of 6 h.In the study of optimization organic load rate?OLR?,the maximum hydrogen production rate of 1.94 L/L/d was achieved under the OLR of 36 kg COD/m3/d,with the COD removal rate of 36.09%-38.28%.The effects of different fixed carriers on the hydrogen production efficiency and treatment efficiency of the system were studied.It was found that the polyurethane exhibited higher hydrogen production rate and higher organic treatment efficiency than zeolite and bioceramic under the same operating con-ditions.The CSTR hydrogen production system of was started with molasses wastewater as sub-strate.After 18 days' start-up and operation,the ethanol-type fermentation process was formed,and the maximum gas production rate of the system could reach 6.15 L/d?34th day?.The maxi-mum hydrogen content in the fermentation gas was 41.51%?29th day?,and the maximum hy-drogen production rate?HPR?was 2.47 L/d?34th day?.Three anaerobic sludge samples were collected for high-throughput sequencing,and the total OTU number was 788.Stable hydrogen production stage had a larger microbial diversity than original anaerobic sludge and acclimated activated sludge.The relative contents of Proteobacteria,Firmicutes,Actinobacteria,Chlor-oflexi,and Bacteroidetes were 48.62%,22.43%,18.43%,2.24%and 2.21%,respectively,and the relative contents of them were 48.62%,22.43%,18.43%,2.24%and 2.01%respectively.The relative content of Hyphomicrobium,Rhodobacteraceae_unclassified,Romboutsia,and Proteiniclasticum were 8.11%,6.07%,5.35%and 3.83%,respectively.The brewery wastewater was used as the substrate to start up the CSTR hydrogen produc-tion system.The ethanol fermentation was formed on the 17th day,and the ethanol-type fer-mentation was maintained in the subsequent operation process.During the start-up operation,the gas production rate of the system is stable at 5.75-6.45 L/L/d,the hydrogen production rate is 2.50-2.72 L/L/d,and the hydrogen content is 39.38%-43.42%.There are 14 categories of microorganisms in hydrogen-producing sludge,in which Saccharibacteria,Proteobacteria,Ac-tinobacteria,Bacteroidetes were the dominant genus,and the relative contents were 49.20%,31.52%,9.36%,3.21%,3.13%and 2.56%,respectively.The microbe can be divided into 220 families,among which Saccharibacteria_norank,Alphaproteobacteria,Betaproteobacteria,Actinobacteria were the dominant,the relative content was 49.20%,12.17%,11.98%,9.36%,respectively.In the optimization test of hydraulic retention time?HRT?of IC hydrogen production sys-tem,the optimum was 4 h,the hydrogen production rate was 1.75 L/L/d,and the hydrogen content was kept in the range of 37.47%-41.77%.During the stable operation of IC system,the removal rate of COD was stable at 34.15%-36.91%,and the stable ethanol fermentation type was maintained.By comparing hydrogen production at different organic loads?24,36,48 kg COD/m3/d?,with the operation of the system,the highest hydrogen production rate of 2.43 L/L/d was achieved at the OLR of 36 kg COD/m3/d.As the system load continues to increase,the hydrogen production rate of the system decreases,so the optimal organic load of the system was determined to be 36 kg COD/m3/d.Molasses wastewater was used as the substrate to start the IC hydrogen production sys-tem,the maximum gas production rate and hydrogen production rate were 16.20 L/d 10.39 L/d.The microbial communities in inoculation stage?L1?and ethanol-type fermentation stage?L5?were studied by high-throughput sequencing.The ACE index and Chao index of L1 were higher than that of hydrogen production sludge sample?L5?,which indicated that the microbial richness and diversity of inoculation sludge were higher.There were 19 phyla in LI,Actinobacteria,Firmicutes,Proteobacteria,Bacteroidetes)were the dominate phyla with the relative content of 66%,14%,12%and 7%.The microbial community in inoculated sludge?L1?was divided into 226 genera,of which 13 genera accounting for more than 0.5%,of which Propionibacterium and Propionibacteriaceae_unclassified were dominant "genera",the rela-tive contents were as high as 50.62%and 12.88%,respectively.In L5,the microorganisms in-creased to 20 phyla,the content of Firmicutes increased to 55%,and the content of Actinobac-teria decreased to 26%.The microorganisms were divided into 230 genera and 14 genera were over 0.5%.Among them,the sum content of Lactobacillus and Propionibacterium was as high as 50.62%.Brewery wastewater was used as the substrate to start the IC hydrogen production system.The maximum hydrogen production rate of the system was 1.31 L/L/d,and the highest net COD removal rate was 28.77%in the first chamber of IC.The maximum gas production rate,hydrogen production rate and hydrogen content of 15.17 L/L/d,7.83 L/L/d and 53.75%were achieved under the OLR of 10.5 10.8?±1.2?kgCOD/m3/d.The removal rate of COD was sta-ble at 35.44%?±4.04?,and the pH was stable at 4.15?±0.09?,which was favored for ethanol-type fermentation.According to the high-throughput sequencing results,the first reactor of the IC reactor had a much higher microbial diversity than that the sludge mixed zone and the sec-ond reactor.Among the three samples,Firmicutes and Proteobacteria were the most abundant at the phylum lever,and the relative contents of Clostridia and Gammaproteobacteria were the highest at class lever.Clostridium_sensustricto_1unclassified and Raoultella_unclassified were the common dominant bacteria at the species lever,and the relative contents were 83.67%,37.32%and 65.0%,respectively.The dominant bacteria in ethanol-type hydrogen-pro-ducing sludge were Xylella with the relative content of 35.43%.