Part of the book: Lactic Acid Bacteria
Anaerobic digestion, a process that ultimately generates methane and carbon dioxide, is common in natural anoxic ecosystems where concentrations of electron acceptors such as nitrate, the oxidized forms of metals and sulphate are low. It also occurs in landfill sites and wastewater treatment plants. The general scheme of anaerobic digestion is well known and comprises four major steps: (i) hydrolysis of complex organic polymers to monomers; (ii) acidogenesis that results in the formation of hydrogen and carbon dioxide as well as non-gaseous fermentation products that are further oxidized to hydrogen, carbon dioxide and acetate in (iii) acetogenesis based on syntrophic metabolism and (iv) methanogenesis. Approaches to the analysis of methane-yielding microbial communities and data acquisition are described. There is currently great interest in the development of new technologies for the production of biogas (primarily methane) from anaerobic digestion as a source of renewable energy. This includes the modernization of landfill sites and wastewater treatment plants and the construction of biogas plants. Moreover, research effort is being devoted to the idea of separating hydrolysis and acidogenesis from acetogenesis and methanogenesis under controlled conditions to favour biohydrogen and biomethane production, respectively. These two stages occur under different conditions and are carried out in separate bioreactors.
Part of the book: Fermentation Processes
The general scheme of anaerobic digestion is well known. It is a complex process promoted by the interaction of many groups of microorganisms and has four major steps: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The aim of the study was to prepare a systematized list of the selected enzymes responsible for the key pathways of anaerobic digestion based on the Kyoto Encyclopedia of Genes and Genomes database resource. The list contains (i) key groups of hydrolases involved in the process of degradation of organic matter; (ii) the enzymes catalyzing reactions leading to pyruvate formation; (iii) the enzymes of metabolic pathways of further pyruvate transformations; (iv) the enzymes of glycerol transformations; (v) the enzymes involved in transformation of gaseous or nongaseous products of acidic fermentations resulting from nonsyntrophic nutritional interactions between microbes; (vi) the enzymes of amino acid fermentations; (vii) the enzymes involved in acetogenesis; and (viii) the enzymes of the recognized pathways of methanogenesis. Searching for the presence and activity of the enzymes as well as linking structure and function of microbial communities allows to develop a fundamental understanding of the processes, leading to methane production. In this contribution, the present study is believed to be a piece to the enzymatic road map of anaerobic digestion research.
Part of the book: Anaerobic Digestion