Among different conversion processes for biomass, biological anaerobic digestion is one of the most economic ways to produce biogas from various biomass substrates In addition to hydrolysis of polymeric substances, the activity and performance of the methanogenic bacteria is of paramount importance during methanogenesis The aim of this paper is primarily to review the recent literature about the occurrence of both acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of particulate biomass to methane (not wastewater treatment), while this review does not cover the activity of the acetate oxidizing bacteria Both acetotrophic and hydrogenotrophic methanogens are essential for the last step of methanogenesis, but the reports about their roles during this phase of the process are very limited Despite, some conclusions can still be drawn At low concentrations of acetate, normally filamentous Methanosaeta species dominate, eg, often observed in sewage sludge Apparently, high concentrations of toxic ionic agents, like ammonia, hydrogen sulfide (H2S) and volatile fatty acids (VFA), inhibit preferably Methanosaetaceae and especially allow the growth of Methanosarcina species consisting of irregular cell clumps, eg, in cattle manure Thermophilic conditions can favour rod like or coccoid hydrogenotrophic methanogens Thermophilic Methanosarcina species were also observed, but not thermophilic Methanosaetae Other environmental factors could favour hydrogentrophic bacteria, eg, short or low retention times in a biomass reactor However, no general rules regarding process parameters could be derivated at the moment, which favours hydrogenotrophic methanogens Presumably, it depends only on the hydrogen concentration, which is generally not mentioned in the literature

The roles of acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of biomass to methane: a review

Anaerobic digestion (AD) is intrinsically a sequential complex chemical and biochemical process, and many factors (microbiological, operational, and chemical) can affect its performance. The great ...

Anaerobic digestion from the viewpoint of microbiological, chemical, and operational aspects — a review

The metagenome of a biogas-producing microbial community of a production-scale biogas plant fermenter analysed by the 454-pyrosequencing technology

Phylogenetic characterization of a biogas plant microbial community integrating clone library 16S-rDNA sequences and metagenome sequence data obtained by 454-pyrosequencing.

The position of high-rate anaerobic technology (HR-AnWT) in the wastewater treatment and bioenergy market can be enhanced if the range of suitable substrates is expanded. Analyzing existing technologies, applications and problems, it is clear that, until now, wastewaters with high lipids content are not effectively treated by HR-AnWT. Nevertheless, waste lipids are ideal potential substrates for biogas production, since theoretically more methane can be produced, when compared with proteins or carbohydrates. In this minireview, the classical problems of lipids methanization in anaerobic processes are discussed and new concepts to enhance lipids degradation are presented. Reactors operation, feeding strategies and prospects of technological developments for wastewater treatment are discussed. Long-chain fatty acids (LCFA) degradation is accomplished by syntrophic communities of anaerobic bacteria and methanogenic archaea. For optimal performance these syntrophic communities need to be clustered in compact aggregates, which is often difficult to achieve with wastewaters that contain fats and lipids. Driving the methane production from lipids/LCFA at industrial scale without risk of overloading and inhibition is still a challenge that has the potential for filling a gap in the existing processes and technologies for biological methane production associated to waste and wastewater treatment.

https://repositorium.sdum.uminho.pt/bitstream/1822/9653/1/Alves_MicBiotech%5b1%5d.pdf

Waste lipids to energy: how to optimize methane production from long‐chain fatty acids (LCFA)

We constructed a mesophilic anaerobic chemostat that was continuously fed with synthetic wastewater containing propionate as the sole source of carbon and energy. Steady-state conditions were achieved below the critical dilution rate of 0.3 d −1 with almost complete substrate degradation. The propionate-degrading methanogenic communities in the chemostat at dilution rates of 0.01, 0.08, and 0.3 d −1 were analyzed using molecular biological techniques. Fluorescence in situ hybridization with archaeal and bacterial domain-specific probes showed that archaeal cells predominated throughout the three dilution rates. Archaeal-16S rRNA gene clone library analysis and quantitative real-time polymerase chain reaction studies showed that hydrogenotrophic methanogen rRNA genes closely related to Methanoculleus was detected at a dilution rate of 0.01 d −1 , whereas rRNA genes closely related to the Methanoculleus and Methanospirillum genera were detected at dilution rates of 0.08 and 0.3 d −1 . The aceticlastic methanogen, Methanosaeta , was detected throughout the three dilution rates. Bacterial-rRNA gene clone library analysis and denaturing gradient gel electrophoresis demonstrated that rRNA genes affiliated with the genus Syntrophobacter predominated at the low dilution rate, whereas rRNA genes affiliated with the phylum Firmicutes predominated at the higher dilution rates. A significant number of rRNA genes affiliated with the genus Pelotomaculum were detected at dilution rate of 0.3 d −1 . The diversity of genes encoding acetate kinase agreed closely with the results of the rRNA gene analysis. The dilution rates significantly altered the archaeal and bacterial communities in the propionate-fed chemostat.

Microbial community of a mesophilic propionate-degrading methanogenic consortium in chemostat cultivation analyzed based on 16S rRNA and acetate kinase genes.

Yuko Mizuno

Papers

Microbial community of a mesophilic propionate-degrading methanogenic consortium in chemostat cultivation analyzed based on 16S rRNA and acetate kinase genes.

Microbial diversity of mesophilic methanogenic consortium that can degrade long-chain fatty acids in chemostat cultivation.