Improved Methanogenic Communities for Biogas Production

Abstract

Last decade advances on methane microbial ecology in natural environments and man-made systems have introduced possibilities and challenges to biogas-producing processes. Mostly restricted to anaerobic environments, methanogens have also been detected in aerobic desertic soils, and their presence in extreme environments, such as hydrothermal vents, soda lakes, and Antarctic sediments, shows how ubiquitous and adapted they are to different environmental conditions. Most known methanogens belong to Euryarchaeota classes, producing methane from acetoclastic, hydrogenotrophic, or methylotrophic pathways. Recently discovered representatives in Thermoplasmata and Halobacteria classes, as well as in Bathyarchaeota and Vestretearchaeota, Phyla brought new insights on methanogenic diversity and their metabolic pathways. Biotechnological application of methanogens has been studied in bioreactors used for treatment of wastewater and waste. These bioreactors can be operated with acidogenesis and methanogenesis occurring in one stage or, with phase separation, acidogenesis followed by methanogenesis, with suspended and/or attached cells. Several factors have been studied to understand and optimize biogas production in bioreactors, such as temperature, organic load, and type of wastewater input. The biogas-producing communities received special attention following the development of metagenomics, metatranscriptomics, and single-cell genomic approaches. Coupled to the discovery of new methanogenic lineages, these methods revealed the complexity of microbial community structure and functions in both natural environments and bioreactors. However, a comprehensive view of these communities is still needed to improve current biogas-producing processes.