Biogas is a renewable fuel produced when microorganisms break down organic matter in the absence of oxygen. It’s composed primarily of methane (40–75%) and carbon dioxide (15–60%), with small amounts of hydrogen sulfide, nitrogen, and water vapor. Because it contains methane, the same energy-carrying molecule in natural gas, biogas can be burned for heat, used to generate electricity, or refined into a direct substitute for natural gas.
How Biogas Is Made
Biogas forms through a process called anaerobic digestion, where bacteria decompose organic material in a sealed, oxygen-free environment. This happens naturally in swamps, landfills, and the guts of ruminant animals, but it can also be engineered in purpose-built tanks called digesters. The process unfolds in four stages, each driven by different groups of microorganisms working in sequence.
First, in hydrolysis, large organic molecules like fats, proteins, and carbohydrates are broken into smaller components. Next, acid-forming bacteria consume those smaller molecules and produce fatty acids and other intermediate compounds. In the third stage, those intermediates are converted into acetate and hydrogen. Finally, methane-producing microorganisms consume the acetate and hydrogen to generate methane, the energy-rich component of biogas. The whole process typically takes two to four weeks in a controlled digester, depending on temperature and what’s being fed in.
What Goes Into a Biogas Digester
Almost any organic waste can serve as feedstock. The most common sources are animal manure, food waste, crop residues, and sewage sludge. Different materials yield different amounts of methane. Cattle manure on its own produces roughly 147–204 liters of methane per kilogram of organic material, while swine manure yields 212–322 liters. Mixing feedstocks together, a practice called co-digestion, consistently improves output. Adding food waste or crop residues to animal manure can boost methane yields by 46% or more compared to digesting manure alone.
This flexibility is one of biogas’s practical advantages. A dairy farm can feed its digester with cow manure and leftover silage. A city can process food scraps from restaurants and grocery stores. A wastewater treatment plant can digest sewage sludge. In each case, waste that would otherwise decompose in the open (releasing greenhouse gases uncontrolled) is captured and converted into usable energy.
Energy Content and Upgrading to Biomethane
Raw biogas has a lower heating value of 16 to 28 megajoules per cubic meter, depending on its methane concentration. That’s roughly half to three-quarters the energy density of natural gas. The carbon dioxide diluting it is the main reason for the gap.
To close that gap, biogas can be “upgraded” by stripping out the carbon dioxide and trace contaminants like hydrogen sulfide. The result is biomethane, which is 95–99% methane and has a heating value of about 36 megajoules per cubic meter. At that purity, biomethane is chemically indistinguishable from natural gas. It can flow through existing pipelines, fuel standard natural gas vehicles, and power conventional gas boilers or appliances without any equipment changes.
Common upgrading methods include water or chemical scrubbing (dissolving the CO2 in a liquid), pressure swing adsorption (trapping CO2 on a solid material under pressure), membrane separation, and cryogenic separation (cooling the gas until the CO2 liquefies). Each approach has trade-offs in cost and efficiency, but all achieve the same end product.
How Biogas Is Used
The simplest use is burning biogas on-site for heat, which is common on farms in developing countries where a small household digester can replace firewood or propane for cooking. At a larger scale, biogas powers combined heat and power (CHP) units that simultaneously produce electricity and capture the waste heat for industrial processes or building heating. This is the dominant model in Europe, where biogas plants often feed electricity into the grid.
Biogas systems also offer something that solar and wind cannot: dispatchable power. Because operators can control the feeding rate and store gas, production can be ramped up when electricity demand peaks, helping stabilize a grid that relies heavily on intermittent renewables. Upgraded biomethane is increasingly used as a transport fuel, particularly for heavy-duty vehicles and long-haul trucks that are difficult to electrify. Compressed biomethane works in the same engines and fueling infrastructure designed for compressed natural gas.
Environmental Benefits
Compared to natural gas, biogas and biomethane supply chains achieve 51–70% lower greenhouse gas emissions on average, according to a 2024 study in Energy & Environmental Science. Those savings come from two directions: the methane burned would have been released into the atmosphere anyway as waste decomposed, and the energy produced displaces fossil fuels.
The climate math is significant because methane is 34 times more potent than carbon dioxide as a greenhouse gas over a 100-year period. Capturing it from manure lagoons or landfills before it escapes into the atmosphere prevents a powerful warming effect, while the carbon dioxide released when the biogas is burned is considered biogenic (part of the short-term carbon cycle, not adding new carbon from underground reserves).
Digestate: The Other Product
Biogas production doesn’t just yield energy. The leftover material, called digestate, is a nutrient-rich slurry containing nitrogen, phosphorus, potassium, and various micronutrients. It has been used as organic fertilizer in agriculture worldwide for decades, replacing synthetic fertilizers derived from fossil fuels. The digestion process also reduces pathogens and weed seeds compared to spreading raw manure, and it cuts down on odor.
Digestate isn’t without concerns. When the feedstock includes animal manure from livestock treated with antibiotics, the digestate can carry antibiotic residues, resistant bacteria, and trace heavy metals like zinc and mercury. Responsible use requires testing and, in many countries, regulatory limits on application rates to prevent soil and water contamination.
Safety Considerations
Biogas is flammable, and because it contains hydrogen sulfide (which is toxic even in small concentrations), leaks from digesters pose both explosion and health risks. Common leak points include membrane connections, cable pass-throughs in digester walls, flange joints, and viewing windows. Operators use methane-sensitive monitors, laser detectors, and infrared imaging to spot leaks invisible to the naked eye. Regular detection surveys are a standard part of plant maintenance.
For homeowners or communities near biogas facilities, the primary concern is odor from hydrogen sulfide, which smells like rotten eggs. Well-maintained systems with proper gas-tight seals and scrubbing equipment rarely produce noticeable odors outside the plant boundary.
Global Production Today
Global biogas production reached 1.76 exajoules in 2023, with generation capacity growing by 4% that year. Europe dominates the sector, accounting for 60% of global biogas investment in 2024. Germany alone operates thousands of farm-scale and industrial digesters. Growth is accelerating in other regions too, with notable expansion in Brazil and India, where agricultural waste is abundant and energy demand is rising.
As countries pursue net-zero emissions targets, biogas and biomethane are increasingly viewed as essential pieces of the puzzle. They offer a way to decarbonize sectors that are hard to electrify, from industrial heat to heavy transport, while simultaneously managing organic waste and producing fertilizer. The technology is mature, the feedstocks are everywhere, and the infrastructure to use the gas already exists.