Biogas is a renewable gaseous fuel generated from organic materials including agricultural residues, manure, municipal waste, plant matter, sewage, wastewater, green waste, and food waste. Biogas is produced industrially via anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester or other type of bioreactor. The gas composition is primarily methane () and carbon dioxide () with small amounts of hydrogen sulfide () produced as a byproduct. Biogas is typically saturated with water vapour as a result of anaerobic micro-organisms living in water. Trace quantities of volatile organic compounds and siloxanes can also vapourize into biogas, if they are present in the biomass feedstock.
Biogas is considered to be a renewable energy resource as the methane can be combusted to release energy. This energy release allows biogas to be used as a fuel. Biogas and its derivatives are used for multiple purposes including heat for cooking, electricity generation, and as a vehicle fuel. At a high level, biogas is a carbon-neutral fuel in so far as emissions of carbon dioxide from its combustion are matched by carbon dioxide pulled from the atmosphere to produce biomass. In practice, the carbon intensity of biogas can vary depending on emissions from the production of biomass and the processes used to produce and upgrade biogas. In some applications, the capturing of biogas can avoid emissions of methane reducing overall emissions.Liebetrau, J., Ammenberg, J., Gustafsson, M., Pelkmans, L., Murphy, J.D. (2022). The role ofbiogas and biomethane in pathway to net zero. Murphy, J.D (Ed.) IEA Bioenergy Task 37, 2022
Biogas can be upgraded to natural gas quality specifications by stripping carbon dioxide and other contaminants. Biogas that has been upgraded to interchangeability with natural gas is called renewable natural gas (RNG). RNG can be used as a drop-in fuel in the gas grid or to produce compressed natural gas as a vehicle fuel.
Production Biogas is produced by microorganisms, such as methanogens and sulfate-reducing bacteria, performing anaerobic respiration. Biogas can refer to gas produced naturally and industrially.
As of 2026, biogas production primarily comes from large-scale industrial plants.
Natural
In soil, methane is produced in anaerobic environments by methanogens, but is mostly consumed in aerobic zones by methanotrophs. Methane emissions result when the balance favors methanogens. Wetland soils are the main natural source of methane. Other sources include oceans, forest soils, termites, and wild ruminants.
Industrial
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. This process produces biogas which can be used as a fuel. Industrial biogas production can either be purpose-built such as anaerobic digesters built to process manure and organic waste or can harvest biogas produced as byproduct from landfills or wastewater treatment plants.
Biogas plants A biogas plant is the name often given to an anaerobic digester that treats farm wastes, municipal organic waste and/or energy crops. Industrial biogas plants process organic material in an air-tight tank to create anaerobic conditions. The material is heated to either mesophilic (~) or thermophilic (>) and held for a typical retention time of two to thirty days. Biogas produced from these facilities is either combusted for electricity production using a combined heat and power system or upgraded to biomethane for use in vehicles or natural gas distribution systems.
These plants can be fed with energy crops such as maize silage or biodegradable wastes including sewage sludge and food waste. Feedstock type significantly influences methane yield: fats and food waste can produce up to 800 m³ of gas per tonne of dry matter, while animal manure yields approximately 20-30 m³ per tonne, though it offers greater process stability. During the process, the micro-organisms transform biomass waste into biogas and digestate. Higher quantities of biogas can be produced when the wastewater is co-digested with other residuals from the dairy industry, sugar industry, or brewery industry. For example, while mixing 90% of wastewater from beer factory with 10% cow whey, the production of biogas was increased by 2.5 times compared to the biogas produced by wastewater from the brewery only.
Landfill gas
Landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a similar way to biogas. The waste is covered and mechanically compressed by the weight of the material that is deposited above. This material prevents oxygen exposure thus allowing anaerobic microbes to thrive. Biogas builds up and is slowly released into the atmosphere if the site has not been engineered to capture the gas. Landfill gas released in an uncontrolled way can be hazardous since it can become explosive when it escapes from the landfill and mixes with oxygen. The lower explosive limit is 5% methane and the upper is 15% methane.Safety Page, Beginners Guide to Biogas , www.adelaide.edu.au/biogas. Retrieved 22.10.07.
The methane in biogas is 28 times more potent a greenhouse gas than carbon dioxide. Therefore, uncontained landfill gas, which escapes into the atmosphere may significantly contribute to the effects of global warming. In addition, volatile organic compounds (VOCs) in landfill gas contribute to the formation of photochemical smog.
Faecal sludge Faecal sludge is a product of onsite sanitation systems. After collection and transport, faecal sludge can be treated as sewage in a conventional treatment plant, or independently in a faecal sludge treatment plant. Faecal sludge can be co-treated with organic solid waste in composting or in an anaerobic digestion system that includes biogas production. Resource Recovery and Reuse is a subprogram of the CGIAR Research Program on Water, Land and Ecosystems. It claims post-processing for energy recovery is economically feasible and would tackle sanitation, health and environmental issues.
Wastewater treatment accounted for 3-4% of US electricity consumption in 2025 (vs 0.5% for electric vehicle charging. Conventional treatment processes issue ~ 21 million metric tons of greenhouse gases annually. About half of the ~15,000 wastewater treatment facilities in the USA use anaerobic digestion, which typically converts <40% of the sludge into biogas. The rest typically is sent to landfills, releasing methane and CO2.
Dangers The content of toxic hydrogen sulfide presents additional risks and has been responsible for serious accidents. Leaks of unburned methane are an additional risk, because methane is a potent greenhouse gas. A facility may leak 2% of the methane.
Biogas forms an explosive mixture with air at concentrations between approximately 6% and 22% by volume. To eliminate this hazard during maintenance, empty digesters must be properly ventilated, cleared of gas, and monitored before entry. Crucially, the system must be designed and operated to prevent negative pressure, which can draw air in and create an explosive atmosphere. This is ensured by technical controls, such as automatic shut-off devices, not merely by avoiding a specific minimum pressure.Bontempo, Giannina; Maciejczyk, Manuel; Wagner, Lucas; Findeisen, Clemens; Fischer, Mareike; Hofmann, Frank (November 2016). Safety first! Guidelines for the safe use of biogas technology. Freising, Germany: German Biogas Association (Fachverband Biogas e.V.) and Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH. PDF. https://www.biogas.org/fileadmin/redaktion/dokumente/medien/broschueren/safety/Safety_Guidelines_english.pdf (accessed 27 October 2023).
Frequent smell checks must be performed on a biogas system. If biogas is smelled anywhere windows and doors should be opened immediately. If there is a fire the gas should be shut off at the gate valve of the biogas system.
Composition +Typical composition of biogasCompoundFormulaPercentage by volumeMethane50–80Carbon dioxide15–50Nitrogen0–10Hydrogen0–1Hydrogen sulfide0–0.5Oxygen0–2.5Source: www.kolumbus.fi, 2007Basic Information on Biogas , www.kolumbus.fi. Retrieved 2.11.07. The composition of biogas varies depending upon the substrate composition, as well as the conditions within the anaerobic reactor (temperature, pH, and substrate concentration). A 2025 study in Ethiopia concluded that agroecology (which influences ambient temperature), biogas plant design, and temperature significantly affect biogas yield quality. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55–75% methane, which for reactors with free liquids can be increased to 80–90% methane using in-situ gas purification techniques. As produced, biogas contains water vapor. The fractional volume of water vapor is a function of biogas temperature; correction of measured gas volume for water vapour content and thermal expansion is easily done via simple mathematics which yields the standardized volume of dry biogas.
For 1000 kg (wet weight) of input to a typical biodigester, total solids may be 30% of the wet weight while volatile suspended solids may be 90% of the total solids. Protein would be 20% of the volatile solids, carbohydrates would be 70% of the volatile solids, and finally fats would be 10% of the volatile solids. Biochemical oxygen demand (BOD) is a measure of the amount of oxygen required by aerobic micro-organisms to decompose the organic matter in a sample of material being used in the biodigester as well as the BOD for the liquid discharge allows for the calculation of the daily energy output from a biodigester.
Contaminants Sulfur compounds Toxic, corrosive and foul smelling hydrogen sulfide () is the most common contaminant in biogas. If not separated, combustion will produce sulfur dioxide () and sulfuric acid (), which are corrosive and environmentally hazardous., Other sulfur-containing compounds, such as thiols may be present.
Ammonia Ammonia () is produced from organic compounds containing nitrogen, such as the amino acids in proteins. If not separated from the biogas, combustion results in emissions.
Siloxanes In some cases, biogas contains siloxanes. They are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or other elements in the combustion gas. Deposits are formed containing mostly silica () or silicates () and can contain calcium, sulfur, zinc, phosphorus. Such white mineral deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means.
Debate
Arguments in favor With simple technology at the household level, the anaerobic fermentation of organic matter produces a stable and non-poisonous fuel which can be used for cooking, lighting, and farm machinery.
High levels of methane are produced when manure is stored under anaerobic conditions. During storage and when manure has been applied to the land, nitrous oxide is also produced as a byproduct of the denitrification process. Nitrous oxide () is 273 times more aggressive as a greenhouse gas than carbon dioxide and methane 27 times more than carbon dioxide.