Effect of Spatial Differences in Microbial Activity, pH, and Substrate Levels on Methanogenesis Initiation in Refuse

Abstract

The initiation of methanogenesis in refuse occurs under high volatile fatty acid (VFA) concentration and low pH (5.5 to 6.25), which generally are reported to inhibit methanogenic Archaea. One hypothesized mechanism for the initiation of methanogenesis in refuse decomposition is the presence of pH-neutral niches within the refuse that act as methanogenesis initiation centers. To provide experimental support for this mechanism, laboratory-scale landfill reactors were operated and destructively sampled when methanogenesis initiation was observed. The active bacterial and archaeal populations were evaluated using RNA clone libraries, RNA terminal restriction fragment length polymorphism (T-RFLP), and reverse transcription-quantitative PCR (RT-qPCR). Measurements from 81 core samples from vertical and horizontal sections of each reactor showed large spatial differences in refuse pH, moisture content, and VFA concentrations. No pH-neutral niches were observed prior to methanogenesis. RNA clone library results showed that active bacterial populations belonged mostly to Clostridiales, and that methanogenic Archaea activity at low pH was attributable to Methanosarcina barkeri. After methanogenesis began, pH-neutral conditions developed in high-moisture-content areas containing substantial populations of M. barkeri. These areas expanded with increasing methane production, forming a reaction front that advanced to low-pH areas. Despite low-pH conditions in >50% of the samples within the reactors, the leachate pH was neutral, indicating that it is not an accurate indicator of landfill microbial conditions. In the absence of pH-neutral niches, this study suggests that methanogens tolerant to low pH, such as M. barkeri, are required to overcome the low-pH, high-VFA conditions present during the anaerobic acid phase of refuse decomposition.

Mitigation of greenhouse gas emission from the cattle manure composting process by use of a bulking agent

“…Therefore, some active aeration into these zones would be required for further CH 4 mitigation. Compared to the water content, the other physical and chemical parameters that might have affected the methanogen composition, such as the C/N ratio or pH (Staley et al 2011), were not significantly different between the experimental and control piles, and thus these parameters would not have made a significant contribution and would not have been the reason for the CH 4 mitigation in the manure compost. On the other hand, the CH 4 mitigation obtained in this study could also be explained by the enhancement of CH 4 oxidation occurring in the pile surface zone.…”

Direct Interspecies Electron Transfer between Geobacter metallireducens and Methanosarcina barkeri

“…Another genus of acetoclastic methanogens, Methanosarcina, is often abundant in methanogenic soils and sediments (23)(24)(25), coal mines (26,27), landfills (28), and anaerobic digesters (29,30). Several studies suggested that Methanosarcina species could accept electrons from nonbiological extracellular surfaces (31,32).…”

Metabolic and microbial community dynamics during the anaerobic digestion of maize silage in a two-phase process

“…The VS c conversion degree in our reactor system was in a similar range like that in comparable two-phase systems (Cysneiros et al 2008), but lower than in one-phase CSTR with maize silage monodigestion (Mähnert 2007). This could be due to spatial differences in percolation systems which can result in inhomogeneous microbial activity and inadequate substrate degradation (Staley et al 2011). Consequently, stirred systems prevail compared to solid-state digesters in full-scale AD of energy crops showing that high-performance hydrolysis and efficient methanogenesis are not mutually exclusive when running simultaneously in one reactor.…”