Short-term effect of acetate and ethanol on methane formation in biogas sludge

Abstract

Biochemical processes in biogas plants are still not fully understood. Especially, the identification of possible bottlenecks in the complex fermentation processes during biogas production might provide potential to increase the performance of biogas plants. To shed light on the question which group of organism constitutes the limiting factor in the anaerobic breakdown of organic material, biogas sludge from different mesophilic biogas plants was examined under various conditions. Therefore, biogas sludge was incubated and analyzed in anaerobic serum flasks under an atmosphere of N2/CO2. The batch reactors mirrored the conditions and the performance of the full-scale biogas plants and were suitable test systems for a period of 24 h. Methane production rates were compared after supplementation with substrates for syntrophic bacteria, such as butyrate, propionate, or ethanol, as well as with acetate and H2+CO2 as substrates for methanogenic archaea. Methane formation rates increased significantly by 35 to 126 % when sludge from different biogas plants was supplemented with acetate or ethanol. The stability of important process parameters such as concentration of volatile fatty acids and pH indicate that ethanol and acetate increase biogas formation without affecting normally occurring fermentation processes. In contrast to ethanol or acetate, other fermentation products such as propionate, butyrate, or H2 did not result in increased methane formation rates. These results provide evidence that aceticlastic methanogenesis and ethanol-oxidizing syntrophic bacteria are not the limiting factor during biogas formation, respectively, and that biogas plant optimization is possible with special focus on methanogenesis from acetate.

Abundance, rather than composition, of methane‐cycling microbes mainly affects methane emissions from different vegetation soils in the Zoige alpine wetland

“…The OM and NN seem to promote the growth of both methanogens and methanotrophs, as they were positively correlated with all abundances (Figure 4) and have positive effects on microbial abundance (Figure 5a). The positive correlation with OM can be easily understood, as the decomposition of OM provides energy and nutrients for microbial growth (Fontaine, Mariotti, & Abbadie, 2003;Refai, Wassmann, & Deppenmeier, 2014). It has been shown that the abundance of methanogens are significantly increased by OM addition (Asakawa, Akagawa-Matsushita, Koga, & Hayano, 1998).…”

Immediate Effects of Ammonia Shock on Transcription and Composition of a Biogas Reactor Microbiome

“…Eight small-scale fed batch reactors used in the experiment were set up as previously described by Refai et al (2014a,b). Briefly, 200 g of biogas reactor material was transferred under anaerobic conditions to 1-L gas-tight glass bottles sealed with butyl rubber stoppers and locked with aluminum screw caps.…”

“…Due to low sampling material amounts, the replicated samples from the four individual reactors per treatment condition and sampling point were combined. Acetate and butyrate concentrations were determined by gas chromatography as previously described (Refai et al, 2014a).…”

Long‐term investigation of microbial community composition and transcription patterns in a biogas plant undergoing ammonia crisis

“…Samples were collected in sealed plastic bottles, transported under cooled conditions and stored in the laboratory at À80°C until nucleic acid extraction. Methane production of the biogas reactor samples was measured as previously described (Refai et al, 2014). Shortly, 20 g of biogas reactor material was transferred into 120 ml serum flasks under anaerobic conditions, sealed with a rubber stopper and purged with N2/CO2 (50/50%, 1 atm) for 10 min.…”