Performance Of Methane Production In Two-stage Anaerobic Digestion And Microbial Ecological Regulation Mechanisms

The depletion of fossil fuel sources and environmental pollution caused by thedevelopment of world economy. It is urgent to seek novel resource utilizationtechnique of using organic wastes to produce renewable energy. Recently, anaerobicdigestion is widely applied to convert biomass waste into methane worldwide, and ithas received considerable economic and environmental benefits. However,application of anaerobic digestion technique mainly depended on traditionalexperience, and lacked of deep mechanism research on microorganisms. Therefore,the anaerobic digester operated at low efficiency and instability due to simpleconfiguration and process tequenology. It was hard for industrial application in lowtemperature regions. Furthermore, biogas slurry was disposed inappropriately couldcaused secondary pollution to environment. Disposal of biogas slurry to producebioorganic fertilizer was inhibited by technique of granulation and irrigation.Thus, based on practical problems and detailed studies during the anaerobicdigestion process, this study designed a two-stage anaerobic digestion system formethane production from cattle dung and co-digestion of rice straw and molasseswastewater. The research discussed the effect of psychrophilic conditions onmethane production and microorganisms via two technique route. The psychrophilicmethanogens were cultivated from natural habits, and domesticated frommethanogenic phase of two-stage anaerobic digesion. Futhermore, the feasibility ofusing of biogas slurry as substrate to produce bioflocculant was discussed. The mainresults obtained by this study were as follow.The acidification-phase using MFC technique could promote degradation andVFA production of cattle dung obviously, and which was beneficial to directionalconversation of VFA. The main VFAs found was acetate which occupied78%oftotal VFAs operated at8%TS, and the propionate concentration was inhibited.Microbial comminity of biofilm analysis revealed that bacteria were dominated byAcinetobacter sp., Pseudomonas sp., and Flavobacterium sp.. The acidified cattledung from40-d operation of acidification-phase were used for IC reactor. Biogasproduction reached1.21±0.047m³m_reactor^-3d^-1, and methane production was252.6±8.4L kg^-1VSfedwhich operated at an OLR of2.5kg VSaddm^-3d^-1and a HRTof40d. The dominant bacteria were Lutaonella sp., Sedimentibacter sp.,Proteiniphilum sp, and Clostridium sp., and archaea dominated by Methanosaeta sp.,Methanosarcina sp. and Methanobacterium formicicum during methanogenesis.Methane production from co-digestion of rice straw and molasses wastewaterwas studied. The ph of acidification-phase decreased dramatically to6.42, and concentration of acetate was3210mg/l which occupied72.2%of total VFAsoperated at8%TS after30days of operation. The dominant bacteria wereFirmicutes, Bacteroidetes and Proteobacteria. Biogas production reached1.12±0.046m³m_reactor^-3d^-1, which operated at a HRT of40d and an OLR of3.5kgVSaddm^-3d^-1. The dominant bacteria were γ-Proteobacteria and Clostridia. Thedominant archaea were Methanosaeta sp..Two group of psychrophilic methanogens were collected from nature habitat.Cumulative biogas production maintained stability after6generations cultivation,and biogas production reached180ml and195ml. The optimum biogas productionwas0.26m³m³reactord^-1operated at18°C. The dominant bacteria of psychrophilicmicrooganisms were Firmicutes and Bacteroidetes. Archaea could be identified wereMethanomicrobiaceae and Methanobacterium sp.. The effect of decreasingtemperature gradually on biogas production of IC reactor was studied. The biogasproduction achieved511.2±15.5and410.1±10.8ml L^-1reactord^-1while operating at25°C and22°C, respectively. The biogas production was fluctuant whiletemperature decreased to20°C. The dominant bacteria were Proteobacteria,Firmicutes and Bacteroidetes while operating at a temperature of30°C,25°C and22°C during a stable process. The most predominant bacteria were Proteobacteria at20°C, accounted for71.36%of total populations. Methanosarcina sp. dominatedduring low temperature operation process. The biogas production of Hailin biogasdigester in cold region reached0.625and0.35m³m_reactor^-3d^-1in winter and summerof operation. The domiant bacteria belonged to Proteiniphilum sp.、Spirochaeta sp.and Wolinella sp., which were found in animal digestive system. Methanosaeta sp.and Methanosarcina sp. were the dominant archaea.Fermentation liquor from different substrates were used to producebioflocculants. The maximum flocculation activity,92.45%was achieved when100-day fermentation liquor of rice straw during a dry fermentation process andconventional bioflocculants medium were mixed at an equal ratio. The bioflocculantyield was4.28±0.13g/L. Notably, Sporacetigenium sp.（46.7%） was the dominantmicrobial population during VFA accumulation time. Use of biogas slurry toproduce bioflocullant, which collected from Hailin digester, two-stage anaerobicdigestion of cattle dung and co-digestion of rice straw and molasses wastewater. Theflocculation activity were52.3%,91.3%and92.1%, while fermentation liquor andconventional bioflocculants medium were mixed at an equal ratio. The bioflocculantyield were1.75±0.03g/L,4.21±0.05g/L and4.18±0.04g/L, respectively.