Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. Biogas is produced by anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester, biodigester or a bioreactor. The gas composition is primarily methane and carbon dioxide and may have small amounts of hydrogen sulfide, moisture and siloxanes. The methane can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used in fuel cells and for heating purpose, such as in cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.
Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In anoxic environments, it is the final step in the decomposition of biomass. Methanogenesis is responsible for significant amounts of natural gas accumulations, the remainder being thermogenic.
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The reaction is represented by this equilibrium:
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.
An acetogen is a microorganism that generates acetate (CH3COO−) as an end product of anaerobic respiration or fermentation. However, this term is usually employed in a narrower sense only to those bacteria and archaea that perform anaerobic respiration and carbon fixation simultaneously through the reductive acetyl coenzyme A (acetyl-CoA) pathway (also known as the Wood-Ljungdahl pathway). These genuine acetogens are also known as "homoacetogens" and they can produce acetyl-CoA (and from that, in most cases, acetate as the end product) from two molecules of carbon dioxide (CO2) and four molecules of molecular hydrogen (H2). This process is known as acetogenesis, and is different from acetate fermentation, although both occur in the absence of molecular oxygen (O2) and produce acetate. Although previously thought that only bacteria are acetogens, some archaea can be considered to be acetogens.
Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies exist: (i) direct partial combustion of methane to methanol and (ii) Fischer–Tropsch-like processes that convert carbon monoxide and hydrogen into hydrocarbons. Strategy ii is followed by diverse methods to convert the hydrogen-carbon monoxide mixtures to liquids. Direct partial combustion has been demonstrated in nature but not replicated commercially. Technologies reliant on partial combustion have been commercialized mainly in regions where natural gas is inexpensive.
Acidogenesis is the second stage in the four stages of anaerobic digestion:
Methanosarcina is a genus of euryarchaeote archaea that produce methane. These single-celled organisms are known as anaerobic methanogens that produce methane using all three metabolic pathways for methanogenesis. They live in diverse environments where they can remain safe from the effects of oxygen, whether on the earth's surface, in groundwater, in deep sea vents, and in animal digestive tracts. Methanosarcina grow in colonies.
Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.
The bioconversion of biomass to mixed alcohol fuels can be accomplished using the MixAlco process. Through bioconversion of biomass to a mixed alcohol fuel, more energy from the biomass will end up as liquid fuels than in converting biomass to ethanol by yeast fermentation.
In biology, syntrophy, syntrophism, or cross-feeding is the cooperative interaction between at least two microbial species to degrade a single substrate. This type of biological interaction typically involves the transfer of one or more metabolic intermediates between two or more metabolically diverse microbial species living in close proximity to each other. Thus, syntrophy can be considered an obligatory interdependency and a mutualistic metabolism between different microbial species, wherein the growth of one partner depends on the nutrients, growth factors, or substrates provided by the other(s).
Digestate is the material remaining after the anaerobic digestion of a biodegradable feedstock. Anaerobic digestion produces two main products: digestate and biogas. Digestate is produced both by acidogenesis and methanogenesis and each has different characteristics. These characteristics stem from the original feedstock source as well as the processes themselves.
Methanobacterium is a genus of the Methanobacteria class in the Archaea kingdom, which produce methane as a metabolic byproduct. Despite the name, this genus belongs not to the bacterial domain but the archaeal domain. Methanobacterium are nonmotile and live without oxygen, which is toxic to them, and they only inhabit anoxic environments.
Methanobrevibacter smithii is the predominant methanogenic archaeon in the microbiota of the human gut. M. smithii has a coccobacillus shape. It plays an important role in the efficient digestion of polysaccharides (complex sugars) by consuming the end products of bacterial fermentation (H2, acetate, formate to some extant). M. smithii is a hydrogenotrophic methanogen that utilizes hydrogen by combining it with carbon dioxide to form methane. The removal of hydrogen by M. smithii is thought to allow an increase in the extraction of energy from nutrients by shifting bacterial fermentation to more oxidized end products.
Greenhouse gas emissions from wetlands of concern consist primarily of methane and nitrous oxide emissions. Wetlands are the largest natural source of atmospheric methane in the world, and are therefore a major area of concern with respect to climate change. Wetlands account for approximately 20–30% of atmospheric methane through emissions from soils and plants, and contribute an approximate average of 161 Tg of methane to the atmosphere per year.
Power-to-gas is a technology that uses electric power to produce a gaseous fuel.
Hydrogenotrophs are organisms that are able to metabolize molecular hydrogen as a source of energy.
Methanogens are a group of microorganisms that produce methane as a byproduct of their metabolism. They play an important role in the digestive system of ruminants. The digestive tract of ruminants contains four major parts: rumen, reticulum, omasum and abomasum. The food with saliva first passes to the rumen for breaking into smaller particles and then moves to the reticulum, where the food is broken into further smaller particles. Any indigestible particles are sent back to the rumen for rechewing. The majority of anaerobic microbes assisting the cellulose breakdown occupy the rumen and initiate the fermentation process. The animal absorbs the fatty acids, vitamins and nutrient content on passing the partially digested food from the rumen to the omasum. This decreases the pH level and initiates the release of enzymes for further breakdown of the food which later passes to the abomasum to absorb remaining nutrients before excretion. This process takes about 9–12 hours.
Autogenerative high-pressure fermentation (AHPD) is a biogas production technique that operates under elevated gas pressure. This pressure is naturally generated by the bacteria and archaea through the gases they release. First described by R. Lindeboom of University of Wageningen (WUR) in 2011, a batch reactor was pressurized to 58 bar, yielding a methane concentration of 96% in the resulting biogas. This method is also commonly referred to as High Pressure Anaerobic Digestion (HPAD) in scientific literature.
Lutispora saccharofermentans, is an anaerobic bacteria. Lutispora saccharofermentans was first isolated from methanogenic enrichment cultures derived from a material collected from a lab-scale methanogenic landfill bioreactor.
