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Environmental and spatial factors affecting microbial ecology and metabolic activity during the initiation of methanogenesis in solid waste .

机译：环境和空间因素影响微生物生态和代谢活动的甲烷生成的起始固体废物。

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摘要

Anaerobic decomposition of organic matter occurs in both natural (e.g., soil, peat bogs, digestive tracts) and engineered (e.g. landfills, anaerobic digesters) ecosystems. The primary end-products of anaerobic decomposition are methane (CH4) and carbon dioxide (CO2). Upon landfilling, rapidly degradable materials within the refuse anaerobically decompose resulting in an accumulation of volatile fatty acids (VFAs) and a commensurate drop in pH to a minimum ranging between 5.5 and 6. These low pH, high carboxylic acid conditions have been shown as inhibitory to methanogenic Archaea in analogous ecosystems such as peat and the rumen. In contrast to these findings, methanogenesis initiation occurs under these conditions, indicating the mechanism by which methane production begins in refuse is poorly understood.;There are two theories for how methane production initiates in landfills. One is that methanogenic Archaea (i.e. methanogens) tolerant to the low pH, high VFA conditions consume acids until the bulk pH is suitable for the establishment of methanogens that grow under pH-neutral conditions. The second theory is that spatially isolated areas of neutral pH exist while bulk pH is acidic and these localized regions of neutral pH act as initiation centers for methanogenesis. The goal of this study was to test these two theories and validate their importance relative to methanogenesis initiation in refuse.;To evaluate methanogen acid tolerance in decomposing refuse, three liquid inocula were derived: (1) refuse just entering active decomposition, (2) well-decomposed refuse and, (3) peat. Under high VFA concentrations, results showed methanogenesis initiation occurred at pH minima of 6.25, 5.75 and 5 for actively decomposing refuse, well-decomposed refuse and peat, respectively. The hydrogenotrophic Methanoculleus genus facilitated methane initiation in actively decomposing refuse (pH 6.25) while Methanosarcina triggered methane production in well-decompose refuse (pH 5.75). In peat, methanogenesis was facilitated by an uncultured Methanosarcinales. This is the first study to fully characterize methanogens responsible for methane initiation under low pH, high VFA conditions and suggests acid tolerance (pH 5--6.25) is relatively common provided sufficient acclimation time. However, methane production rates at lower pH were found to be 3 to 6 fold lower than those at neutral pH.;To evaluate the spatial influences on methanogenesis initiation, fresh refuse was placed into triplicate laboratory scale reactors, decomposed to the anaerobic acid phase, and destructively sampled when methanogenesis initiated. Large differences were observed spatially in refuse pH, moisture content and VFA concentration. No pH neutral niches were observed in reactors prior to methanogenesis. RNA clone library results showed most bacterial activity was attributed to the Clostridiales order. Methanogenic Archaea activity at low pH was catalyzed by Methanosarcina barkeri. After methanogenesis, pH neutral conditions developed in high moisture content areas containing substantial populations of M. barkeri. These areas expanded with increasing methane production, forming a unified reaction front that advanced into low pH areas. In the absence of pH neutral niches, this study suggests methanogens tolerant to low pH, such as M. barkeri , are required to overcome the low pH, high VFA conditions typically present during the anaerobic acid phase of refuse decomposition.
机译：有机物的厌氧分解发生在自然（例如土壤，泥炭沼泽，消化道）和工程（例如垃圾填埋场，厌氧消化器）生态系统中。厌氧分解的主要最终产物是甲烷（CH4）和二氧化碳（CO2）。填埋后，垃圾中可快速降解的材料厌氧分解，导致挥发性脂肪酸（VFA）积累，pH值相应下降至5.5至6之间的最小值。这些低pH，高羧酸条件已显示出抑制作用在类似生态系统（例如泥炭和瘤胃）中产甲烷的古生菌。与这些发现相反，在这些条件下发生甲烷生成，这表明人们对垃圾中甲烷产生的机理了解甚少。垃圾填埋场中甲烷的产生有两种理论。一种是能耐受低pH值，高VFA条件的产甲烷古细菌（即产甲烷菌）会消耗酸，直到大量pH值适合建立在pH中性条件下生长的产甲烷菌为止。第二种理论是存在中性pH的空间隔离区域，而整体pH呈酸性，而这些中性pH的局部区域充当甲烷生成的起始中心。这项研究的目的是检验这两种理论，并验证它们相对于垃圾中甲烷生成的重要性。为了评估分解垃圾中甲烷生成酸的耐受性，得出了三种液体接种物：（1）垃圾刚刚进入活性分解状态，（2）腐烂的垃圾，以及（3）泥炭。在高VFA浓度下，结果显示甲烷分解起始发生在pH最小值为6.25、5.75和5时，分别用于主动分解垃圾，分解良好的垃圾和泥炭。氢营养型甲烷菌属促进了甲烷的主动分解（pH 6.25），而甲烷甲烷藻触发了分解良好的垃圾（pH 5.75）中甲烷的产生。在泥炭中，未经培养的甲烷八叠球菌促进了甲烷生成。这是第一个充分表征甲烷甲烷在低pH值，高VFA条件下引发甲烷的特征的研究，并建议在足够的适应时间下耐酸性（pH 5--6.25）相对普遍。但是，发现在较低pH值下的甲烷生成速率比在中性pH值下的甲烷生成速率低3到6倍。为了评估对甲烷生成起始的空间影响，将新鲜垃圾放入一式三份的实验室规模反应器中，分解为厌氧酸相，甲烷生成开始时进行破坏性采样。在空间上观察到垃圾pH，水分含量和VFA浓度差异很大。在甲烷化反应之前，在反应器中未观察到pH中性壁ni。 RNA克隆文库结果表明，大多数细菌活性均归因于梭状芽胞杆菌。甲烷甲烷八叠球菌（Methanosarcina barkeri）催化低pH值下产甲烷的古生菌活性。产甲烷后，在含有大量巴氏支原体的高水分含量区域发展了pH中性条件。这些区域随着甲烷产量的增加而扩展，形成了统一的反应前沿，并发展到低pH值区域。在没有pH值中性利基的情况下，这项研究表明需要耐受低pH值的产甲烷菌，例如M. barkeri，才能克服通常在垃圾分解厌氧酸阶段出现的低pH和高VFA条件。

著录项

  • 作者

    Staley, Bryan Fleet.;

  • 作者单位

    North Carolina State University.;

  • 授予单位 North Carolina State University.;
  • 学科 Engineering Environmental.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 234 p.
  • 总页数 234
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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