Biogas is a renewable fuel produced when microorganisms break down organic matter in the absence of oxygen. It’s primarily a mixture of methane (50 to 75%) and carbon dioxide (25 to 50%), with small amounts of nitrogen, hydrogen sulfide, ammonia, and water vapor. Because of its methane content, biogas burns much like natural gas and can be used for electricity, heating, cooking, and vehicle fuel.
What Biogas Is Made Of
The exact makeup of biogas depends on what organic material went into producing it, but methane and carbon dioxide always dominate. Real-world measurements across different biogas sources show methane ranging from about 50% to 70%, with carbon dioxide filling most of the remainder at 20% to 47%. Nitrogen typically makes up less than 8%, and oxygen stays below 0.5%.
The trace gases matter more than their small percentages suggest. Hydrogen sulfide, even in tiny concentrations, is corrosive and can damage engines and pipelines. Ammonia, siloxanes (compounds found in products like cosmetics and detergents that end up in waste streams), and water vapor also need to be managed before biogas can be put to most practical uses. The proportions of these impurities shift depending on the feedstock and the conditions inside the digester.
How Biogas Is Produced
Biogas forms through anaerobic digestion, a natural process that happens wherever organic material decomposes without air. Think of a compost pile, but sealed off from oxygen. The process unfolds in four stages, each driven by different communities of microorganisms working in sequence.
In the first stage, hydrolysis, bacteria break down complex organic molecules like fats, proteins, and carbohydrates into simpler sugars, amino acids, and fatty acids. During the second stage, acidogenesis, another group of bacteria converts those simpler molecules into volatile fatty acids, alcohols, and gases like hydrogen and carbon dioxide. The third stage, acetogenesis, transforms those intermediate products into acetic acid, hydrogen, and more carbon dioxide. Finally, in methanogenesis, specialized microorganisms called methanogens consume the acetic acid and hydrogen to produce methane, the energy-carrying component of biogas.
This entire chain happens inside sealed tanks called digesters at wastewater treatment plants, farms, and industrial facilities. It also occurs naturally in landfills, where buried organic waste decomposes underground and produces landfill gas, a form of biogas that’s often captured through extraction wells.
What Goes Into a Biogas System
Almost any organic material can serve as feedstock for biogas production. The major categories include animal waste (dairy manure, poultry litter), food processing waste, municipal solid waste, wastewater sludge, agricultural residues like straw and chaff, and dedicated energy crops grown specifically for digestion.
Not all feedstocks produce equal amounts of methane. Fodder beet, for example, yields 420 to 500 cubic meters of methane per tonne of volatile solids, making it one of the highest-performing energy crops. Maize whole crop produces 205 to 450, grass ranges from 298 to 467, and straw comes in at 242 to 324. Among food-related materials, banana fruit and stems generate roughly 940 liters of biogas per kilogram of dry weight, while potato tubers yield about 880 liters. These differences drive real decisions about which feedstocks to use in commercial digesters.
In practice, many biogas plants co-digest multiple feedstocks together. Mixing animal manure with food waste or energy crops often boosts overall gas production and keeps the microbial community stable.
Upgrading Biogas to Biomethane
Raw biogas, with its 50 to 65% methane content, has a lower energy density than natural gas. The carbon dioxide dilutes its heating value significantly. To make biogas interchangeable with conventional natural gas, it goes through a process called upgrading, which strips out the carbon dioxide along with hydrogen sulfide, water vapor, ammonia, siloxanes, and particulates.
The result is biomethane, sometimes called renewable natural gas (RNG), with a methane concentration high enough to meet pipeline quality standards. Biomethane can be injected directly into existing natural gas grids, compressed for use as vehicle fuel, or even converted into methanol for shipping fuel. This flexibility is what makes biomethane particularly valuable: it slots into infrastructure that already exists, without requiring new engines, pipelines, or appliances.
How Biogas Is Used
The simplest and most common use is burning biogas on-site to generate electricity and heat simultaneously through combined heat and power (CHP) systems. A farm with a manure digester, for instance, can power its own operations and sell surplus electricity back to the grid. Biogas-fueled generators can also ramp up production when electricity demand spikes, giving grid operators a dispatchable renewable energy source, something wind and solar cannot always provide.
Beyond electricity, upgraded biomethane fuels compressed natural gas vehicles, particularly in bus fleets and heavy transport where electrification is harder to implement. It also serves as a feedstock for industrial heat in sectors like food processing and manufacturing. Long-distance heavy transport and shipping are emerging applications, since liquid fuels derived from biomethane can replace diesel and marine fuel oil in ways that batteries currently cannot.
Environmental Benefits
Biogas systems reduce greenhouse gas emissions in two distinct ways. First, they capture methane that would otherwise escape into the atmosphere from manure lagoons, landfills, and food waste. Methane is roughly 80 times more potent than carbon dioxide as a greenhouse gas over a 20-year period, so preventing its release has an outsized climate impact. Second, when biogas displaces fossil fuels, it avoids the emissions from extracting and burning coal or natural gas.
Life cycle analyses comparing biogas power plants to coal power plants illustrate the scale of this difference. For the same amount of energy produced (about 15.3 million megajoules), a coal plant emits roughly 33.3 million kilograms of carbon dioxide equivalent in greenhouse gases. A biogas plant producing the same energy registers near-zero net greenhouse gas emissions because the carbon released during combustion was recently absorbed from the atmosphere by the plants or consumed by the animals that generated the waste. The biogas system also produces about three times less particulate matter and roughly one-seventh the sulfur dioxide of coal.
There’s also a waste management benefit. Anaerobic digestion reduces the volume of organic waste, kills many pathogens in the process, and produces a nutrient-rich digestate that works as fertilizer, closing the loop between waste and agriculture.
Global Production Today
Germany is the world’s largest combined biogas and biomethane market, producing 329 petajoules in 2024, though its output has plateaued since around 2017. The United States leads in biomethane specifically, with production growing 2.2-fold since 2020, driven largely by landfill gas capture and dairy manure digesters incentivized by renewable fuel credits. France, Italy, and Denmark are among the fastest-growing markets in Europe.
The technology scales from a single household digester in rural India or sub-Saharan Africa, producing enough gas for daily cooking, all the way up to industrial facilities processing hundreds of tonnes of organic waste per day. This scalability is one of biogas’s defining strengths: it works in places with no electricity grid and in countries with sophisticated energy infrastructure alike.