| Biological hydrogen production from organic wastewater has dual effect ofwastewater treatment and energy recovery. In current, this research subject hasreceived increasingly attention. Among different biological processes for hydrogenproduction, anaerobic fermentation is the most commercially feasible H2biologicalproduction method because of its potential of direct use of wastewater streams andorganic wastes and its high production rate Considering the key problems of thecurrent anaerobic fermentative hydrogen production process and the operationalcontrol methods, a new process entitled “anaerobic contact reactor (ACR)” wasdeveloped in this thesis. The present study attempted to investigate the performanceand control strategy of fermentative hydrogen production in ACR. The operationconditions and methods for establishing ethanol-type fermentation and acceleratingstart-up of ACR were highlighted in this study. Moreover, the mechanism of theformation of climax microbial community of the fermentative hydrogen productionwas revealed from the perspective of microbial ecology. At last, the significance ofhydrogen sink by homoacetogenesis was evaluated and the method of inhibition ofhomoacetogens was investigated， which was aimed to improve the hydrogenproduction capability of ACR.The novel invented hydrogen production process was comparised with acontinuous flow stirred tank reactor (CSTR) and a settler. The system had a bettercapability of holding higher biomass concentration since the sludge was recoveriedinto CSTR from the sedimentation tank, which promises that the ACR system couldoperate at high organic loading rate (OLR) and exhibit an excellent hydrogenproduction. In order to explore the feasibility of using this novel ACR system foranaerobic fermentative hydrogen production, the reactor was started-up with thechemical oxygen demand (COD) of5000mg/L and hydraulic retention time (HRT)of6h at35oC for the first time. The seed sludge used in this section was taken froma secondary sedimentation tank of a local beer wastewater treatment plant. Theresult showed that an ethanol-type fermentation type was established and the systemcould reach steady-state after55days of operation. After the reactor achievedsteady-state, the performance of ACR under OLR ranged from28to44kgCOD/m~3·d was evaluated. It showed that the Ethanoligenens harbinense YUAN-3turned to be more abundance as the influent COD increased, and the specifichydrogen production rate (SHPR) increased to3.51±0.45m~3/m~3·d when OLR wasincreased to44kgCOD/m~3·d.The characteristics of the microbial commnnity of the seed play a decisive role in the start-up proceeding of the fermentative hydrogen productiong systems and themetabolic pathway of the climax microflora. The results showed that ethanol-typefermentation occurred in all the three reactors seeded with different inoculums. Theseed sludge were collected from secondary sedimentation tank of a local beerwastewater treatment plant (R1), anaerobic acidogenic reactor (R2) and sewagesludge (R3), respectively. The reactors were operated under indentical conditions(HRT8h,COD5000mg/L). The results of molecular biology analysis showed thatthe species of microorganisms of R2was the most, followed by R1and R3, but theEthanolgenesis harbinense Yuan-3was most predominant in R3reaction system.Thus, the R3system gave both the highest hydrogen production rate of14.0L/d andspecific hydrogen production of sludge of11.1mmol H2/g VSS·d.When used the untreated, heat-shock and the aeration treated excess activatedsludge as seed sludge for starting up the ACR system, all the reactors could reachsteady-state and estabilish stable fermentative hydrogen producing microorganismin the systems under HRT of8h and COD of5000mg/L. Experimental resultsshowed that the species of microorganisms and the quantity of Ethanoligenensharbinense were the largest in the microbial community in the reactor which wasinoculated the sludge treated by aeration. As result, the hydrogen production ratewas the largest (16L/d) than the other two systems which inoculated the untreatedand heat-shock treated sludge. The results of the above experiments indicated thatthe microbial community would both change in the batch and continuous-flowfermentation hydrogen production system. The seed inocula collected from differentsources and the inoculated sludge treated by various pretreatment methods haddifferent original microbial community and the results indicated that the topmicrobial community of ethanol-type fermentation and butyrate-type fermentationwas directly dependent on the initial microbial community structure of theinoculums.The initial start-up sludge loading rate, pH and influent COD/N has indenpentsignificant influence on the performance of fermentative hydrogen production ofACR. The results found that the ACR could reach steady-state with ethanol-typefermentation only after14days of operation when the initial F/M ratio, COD, pH,influent COD/N and HRT was controlled at1.5gCOD/gVSS·d,5000mg/L,4.3-4.5,200and8h, respectively. On this basis, the influent COD and HRT of ACR systemwere further optimized for hydrogen production by response surface methodology.The result showed that the highest HPR of5.8m~3/m~3·d of the hydrogen productionreactor system was achieved when the OLR was63kgCOD/m~3·d, i.e. COD andHRT was controlled at11.3g/L and4.3h, respectively. As compared to the CSTR(with inner separator), the ACR had a better capability of holding bioamass and it isa promising bioprocess for fermentative hydrogen production. The hydrogen production could be influenced by the homoacetogenesis in thehydrogen production system by anaerobic mixed microflora. While, the activity ofhomoacetogenes could be inhibited by chloroform. The hydrogen production couldbe improved when adding chloroform into the the hydrogen production system.Experimental results showed that the role of hydrogen consumption byhomoacetogenesis significantly affect the hydrogen production, when used theinoculum that was collected from a local beer wastewater treatment plant. It foundthat the Eubacterium limosum and Eubacterium sp. SA11which were classified tohomoacetogens were disappeared in the profile of microbial community, while theEthanoligenens harbinense YUAN-3were enriched after additing0.1%(v/v)chloroform into the fermentative hydrogen system. The result showed that thespecific hydrogen production of the sludge was increased from11.7ml H2/gVSS·dto113.8ml H2/gVSS·d as the homoacetogenesis was inhibited by chloroform. Thehydrogen yield was increased from0.14molH2/mol-glucose to1.07molH2/mol-glucose simultaneously. |
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