厌氧耗氢产甲烷混合菌群还原二氧化碳合成甲烷工艺及机理研究

Hydrogenotrophic methanogens dominated ex-situ microbiological biogas upgrading could not only achieve efficient conversion but also avoid methanogenesis inhibition due to VFAs accumulation and increased pH, thus giving advantages over in-situ upgrading. Considering that hydrogenotrophic methanogens are thermophilic microbes and might be easily influenced by reducing gas such as hydrogen sulfide and ammonia produced during anaerobic digestion, this project proposes to investigate ex-situ microbiological biogas upgrading in a separate anaerobic reactor by contacting hydrogen, carbon dioxide and enrichment cultures of hydrogentrophic methanogens. In this study, metabolic pathway, kinetics and mass transfer efficiency, and predominant microbial community under different ecological niche (thermophilic, hyper-thermophilic, presences of gases like hydrogen sulfide, ammonia, and methane) are examined. Moreover, optimal packing media and modified particles will be selected according to the mass transfer and bioconversion capability. With the obtained results, anaerobic rotating packed bed will be constructed and operated continuously under different conditions to explore the mass transfer characteristics and conversion efficiency. The microbial community structure, functional genes composition and distribution of hydrogenotrophic methanogens in the biofilm and suspended sludge will be examined by metagenomic analysis and Fluorescence in situ hybridization (FISH) technology, which will reveal the microbial metabolism in the mixed enrichment cultures. Meanwhile, mathematical model will also be developed to describe mass transfer and biochemical reactions occurred in the ex-situ system and applied for optimizing practical operation. The project will provide theoretical foundation and technical support for the application of ex-situ biogas upgrading, and enrich the knowledge of anaerobic biological treatment.

采用优势耗氢产甲烷菌，对厌氧消化产生的沼气进行异位生物提纯，可以避免原位生物提纯过程中pH升高，有机酸累积从而影响有机物厌氧消化等问题，并能获得较高的转化效率。本申请在前期研究的基础上，针对耗氢产甲烷菌多为嗜热菌属，以及沼气产生伴随还原性气体硫化氢、氨氮的产生，系统研究不同生境下（高温、超高温、还原性气体赋存）厌氧耗氢产甲烷混合菌群还原二氧化碳合成甲烷的条件调控和转化动力学，探明体系中关键酶活性、代谢途径及优势微生物群落特点；筛选适合生物转化及传质填料，探索采用厌氧滚筒填料床实现气体的高效传质转化，考察工艺运行特性及添加改性颗粒对气体利用效率、甲烷产率的影响；结合宏基因组测序等分子生物学手段探究异位提纯过程中微生物菌群变化规律，多菌的互营关系及代谢功能，并建立相关的传质-反应动力学模型，反馈优化实际操作。研究成果可为异位沼气生物提纯技术的工程应用提供技术支持和理论依据，并丰富厌氧消化理论。

与传统厌氧消化过程中的耗乙酸产甲烷途径不同，耗氢产甲烷途径所涉及的核心菌群间的协作关系，以及工况参数优化等方面仍需要探索。本研究旨在研究不同环境因子（温度、pH、还原性气体）下厌氧耗氢产甲烷代谢途径、转化动力学特性、微生物群落结构的迁移变化规律。温度和pH值是影响H2/CO2生物甲烷化的关键因素，对微生物尤其是古细菌群落有重要影响。随着温度从20°C升高到70°C，优势古菌由甲烷杆菌（67.6%）转变为甲烷热杆菌（97.7%）。然而，pH值为8.5-9.0的碱性条件选择了甲烷杆菌，尤其是在55°C时。CO转化为CH4的转化率为83-97%。长期5%的共驯化将滞后期从55℃的5小时缩短到1小时，70℃的15小时缩短到3小时。对于产氢产甲烷菌来说，CO2是首选的碳源，而不是CO，只有当CO2完全耗尽时才开始消耗CO。尽管CO的引入对产氢产甲烷菌群的影响不大，在产氢产甲烷菌混合培养中，乙酸氧化与产氢产甲烷是细菌与古生菌间的重要共营养途径。.选择传质好、生物持有量高的厌氧转筒反应器进行耗氢产甲烷实验，探究进气负荷与潜在氢源的重要组分CO对反应器运行特性的影响，并从微生物群落结构演替的微观角度对连续流产甲烷过程进行解析。对比不同形式的耗氢产甲烷反应器数据可以发现，水平转筒反应器的最大甲烷产率为11.6±0.3 L-CH4/Lreactor-day、氢气利用率高达95%，在运行参数上具有显著优势。甲烷日均产气量随着负荷的增加而升高，但过高的负荷会影响产甲烷效能。CO的引入增加了细菌的多样性，增强了细菌群落与主要产甲烷古菌M. thermautotrophicus的互营协作关系。上述研究结果可为基于外源供氢的耗氢产甲烷工艺的调控提供理论基础和技术支撑。