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What is "biogas"?

Biogas is the type of gas that is produced in an anaerobic digester. Biogas is mostly made of methane and carbon dioxide plus small amounts of some other gases. Biogas generally contains 55%-75% methane and 44%-24% carbon dioxide, with the other gases making up 1% or less of the mixture. Since biogas is made from organic material, it is sometimes also called “renewable natural gas.” Click here to learn more about biogas.

How is biogas used?

Biogas is lighter than liquid and rises to the top of the digester. From the top of the digester, tubes and pipes allow the biogas to slowly release from the tank into a container so it isn’t released into the air. Biogas can be used as fuel for a boiler to generate hot water or steam, or for an engine to power an electric generator to generate electricity. Biogas can also be “scrubbed”, meaning the carbon dioxide and other non-methane “contaminants” are removed, leaving purer methane gas. Methane is the prime component of natural gas so this scrubbed biogas can then be pressurized and injected in an existing natural gas pipeline, liquefied for other storage or even used as a vehicle fuel..

Is biogas toxic?

You shouldn’t breathe biogas. Biogas, due to its methane content, is flammable and should be dealt with in a safe and secure manner. Some of the trace gases that make up about 1% or less of biogas are acidic and can be corrosive to certain kinds of metals and need to be dealt with carefully. gs.

Is biogas a kind of renewable energy?

Yes. Anaerobic digester technology is employed world-wide to create renewable energy. Biogas produced from an anaerobic digester is comprised primarily of methane gas, which can be used instead of fossil fuels to produce energy. This “renewable natural gas” can substitute for fossil fuel natural gas for any need including heating, cooking and driving. Biogas can also be used as fuel to make clean electricity. All of these options provide us with the opportunity to turn organic “waste” and into a valuable renewable energy resource in a sustainable manner.

Isn't methane a greenhouse gas?

Methane is a greenhouse gas that is more than 20 times as damaging to the environment as carbon dioxide, but it has to be released into the air and atmosphere to take part in the “greenhouse effect.” That is why people who run anaerobic digesters are very careful to contain the biogas and not let it be released into the air—it should be used for energy! One of the benefits of anaerobic digestion is its ability to capture the methane that would normally be emitted into the air if the organic material was left to decompose in an uncontrolled landfill.

Anaerobic Digesters

What is "anaerobic digestion"?

Anaerobic digestion is the process by which naturally occurring bacteria, which can only live in places where there is no air, break down organic, biodegradable material over time and converts it to biogas and a natural fertilizer. In fact anaerobic means “no oxygen.”  Click here to learn more about anaerobic digestion.

What is an "anaerobic digester"?

An Anaerobic Digester is a large, air-tight container or tank that contains no oxygen. The tank is filled with organic material and maintained at an optimum temperature for anaerobic bacteria to digest the material. Depending on what you put into it, the contents can be wet or dry.

How big is an anaerobic digester?

From the size of a large refrigerator to the size of small building. The size of the digester depends on how much organic material will be fed into the digester, and how quickly that specific digester can break down the organic material.

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How many operational anaerobic digesters are there in the U.S.?

The U.S. has over 2,200 sites producing biogas: 250 anaerobic digesters on farms, 1,269 wastewater treatment plants using an anaerobic digester (~860 currently use the biogas they produce), 66 standalone (non-agriculture and non-wastewater) anaerobic digesters, and 652 landfill gas projects. The potential for U.S growth is huge. We count nearly 13,500 sites ripe for development today: 8,241 dairy and swine farms and 3,888 wastewater treatment plants (including ~380 who are making biogas but not using it) which could support a digester and 440 untapped landfill gas projects. For comparison, Europe has over 10,000 operating digesters and some communities are essentially fossil fuel free because of them. If fully realized, these biogas systems could produce enough energy to power 3.5 million American homes and reduce emissions equivalent to removing 800,000 to 11 million passenger vehicles from the road.

How many anaerobic digesters are there in operation the rest of the world?

It is hard to say exactly, but the number is in the hundreds of thousands or over a million. Anaerobic digesters are at work on every continent except Antarctica. Countries like India, China, and some Western European countries have been employing anaerobic digesters for decades.

What makes an anaerobic digester work?

The key is to keep the microscopic bacteria, which break down the material fed into the digester, living and constantly multiplying inside the digester. The bacteria require a sufficient amount of organic feedstock, vitamins, supplements, and some water to live. The bacteria also thrive in a warm environment without large fluctuations in the acidity levels. Like all living things, the bacteria work better without toxins.

Does something specific have to be grown to feed into an anaerobic digester?

Certain crops like corn and grasses can be used to feed anaerobic digesters, but most organic waste materials like manure, and food scraps work even better than specially grown crops.

Are digesters cold or hot?

To keep the right bacteria alive and multiplying, many of the larger digesters are kept at or above 30 to 38 degrees Celsius or 86 to 100 degrees Fahrenheit. Digesters can also work at temperatures that are both lower and higher than this. Because the bacteria working in the digester are very sensitive to temperature, cooler digesters take more time to break down the biodegradable feedstock, while hotter ones may break down the biodegradable feedstock more quickly.

What kinds of material can be digested in an anaerobic digester?

Theoretically, any organic material can be broken down through anaerobic digestion. Wasted or spoiled food, plant clippings, animal manure, meat trimmings, and sewage after it’s been treated are especially well suited to this type of digestion. Inorganic material such as rocks and dirt, and man-made materials such as plastic, metal cans, and glass, will not be broken down through anaerobic digestion. In addition, woody wastes do not digest well because their strong fibers are naturally resistant to degradation and also the anaerobic bacteria.

How long does it take to break down the organic material in the digester?

It varies based on the type of organic material you feed into the digester and the design of the digester. Simpler organic compounds, such as simple sugars, fats and proteins, will digest fairly quickly. More complex organic compounds may take 30 plus days to completely digest, especially fibrous materials like cellulose, the major constituent of paper, paperboard, and card stock and of textiles made from cotton, linen, and other plant fibers), . The operating temperature of the digester also has a significant impact on the time it will take to break down the material.

What is organic material?

Organic material is something that was living and can decay. Wasted or spoiled food, plant clippings, animal manure, meat trimmings, and sewage are common types of organic material used with Anaerobic digestion. In contrast, inorganic material includes things like rocks, dirt, plastic, metal and glass.

By "organic" do you man "Certified Organic" food?

No. By “organic” we mean what chemists refer to as an “organic” material – the carbon-based material from which all living things are made. Man-made materials such as plastic and glass, and some other natural materials like rock, sand, metals, and dirt are called “inorganic materials”. Inorganic materials will not be broken down in an anaerobic digester.

What materials yield the most biogas?

When put into an digester, fats, oils and greases (industry lingo: FOGs) and food waste create the most biogas. For this reason, many dairy farms that have digesters add local food scraps to the manure in their digesters to increase the amount of biogas produced. Digesting different materials is called co-digestion. (Image source: Basisdaten Biogas DeutchlandThe Climate TrustBioCycle and OWS, Inc.)

How can I get involved in promoting anaerobic digestion in America?

Contact us at info@americanbiogascouncil.org. If you would like to become a member of the American Biogas Council, or if you would care to learn more about our council, please click on “Become a Member” at the top of this page. Anyone can join and your membership dues will be used to advance biogas and anaerobic digestion as a renewable energy technology in America.

Is there a wholesale price for renewable natural gas (RNG) sold for vehicular fuel?

Typically, the producer can expect to receive avoided cost of cogeneration (COG, i.e, the commodity) plus a negotiated percentage of the value realized from sale of the RIN (renewable identification number attached to the gallon equivalent of fuel) and LCFS (low carbon fuel standard) credit, if in CA, associated with the amount of gas produced.

That price will of course be variable month to month. A fixed, wholesale price for RNG that will be sold as vehicle fuel doesn’t exist at this time. To create it, any seller of RNG vehicle fuel would have to risk (or somehow hedge) their exposure to variable RIN, LCFS and NG commodity pricing (which is based on what the market will bear at any one time) in order to offer a fixed price to the producer.

Environmental Benefits

What are the environmental benefits of biogas?

Biogas systems are one of the most effective solutions for waste management. They protect our climate, air, water, and soil by recycling organic material, like food waste and manure, into renewable energy and soil products while also reducing GHG emissions.

Without biogas systems, tons of carbon emissions would be released into our air, and more fossil fuels would be used to fuel our economy and create synthetic fertilizers to grow our crops. When operated properly, biogas systems create healthier soils by returning nutrients to the earth and producing reliable, carbon-offsetting, baseload renewable energy. While there are many sources for renewable electricity, and the U.S. has large stores of natural gas, biogas systems do something these other sources can’t – recycle the massive volumes of food waste in this country, which makes up 30-40% of all garbage in the U.S., as well as other organic wastes from farms and water treatment facilities. Without biogas systems, these waste streams, when unmanaged, create a host of environmental issues.

How do biogas systems help our climate and air?

Biogas systems dramatically reduce odor from common waste materials and treat other air contaminants, like hydrogen sulfide, while reducing greenhouse gas (GHG) emissions. Moving manure from open lagoons to a covered, airtight biogas system significantly reduces naturally occurring GHG emissions via its capture and conversion to renewable electrical, thermal, or liquid forms of energy or fuel. Most biogas systems reduce carbon emissions in transportation by about half compared to fossil fuels. The least GHG emitting biogas systems are so carbon negative they reduce carbon emissions six times more than a battery-electric vehicle running on 100% wind or solar power compared to a gasoline vehicle.

How do biogas systems help our water?

Biogas systems, when properly operated, can help the farmer to optimize the volume and ratio of nutrients used in the soil. During the digestion process, several physical, chemical, and biological conversions take place. The resulting digestate has odor and pathogens virtually eliminated and more importantly produces a readily available form of nutrients in the soil. This may allow farmers to target more precise application of these nutrients. This provides the potential for increased crop yields while reducing environmental losses. Additionally, the qualities of the digestate facilitate the use of solids/nutrient separation technologies that can further aid optimization of nutrient application in the soil and reduce the needs for synthetic fertilizers produced from fossil fuels.

How do biogas systems help our soil quality?

Biogas systems recycle manure while producing renewable energy and soil products. Digestate, the material remaining after the digestion process, can be used, or sold as fertilizer and has been shown, in some studies, to boost crop yields by 10-30%, reducing the need for chemical fertilizers. Nutrients in digested material are more readily absorbed by plants compared to raw manure. In addition, nutrient capture systems can be added on to biogas systems. It also is easier to remove excess nitrogen or phosphorus nutrients from digested manure than from raw manure because many chemical bonds have been broken. This allows farmers to use the right volume and ratio of nutrients needed and minimize the additional purchase of synthetic fertilizers. In addition, the carbon contained in the organic matter that makes up the digestate helps to restore or improve the organic matter content of the soils where it’s applied.

How does biogas help reduce effects of climate change?

Biogas is made up of methane and carbon dioxide, which are powerful greenhouse gases. If not processed in a biogas system, the organic waste our society produces would naturally generate these gases. Anaerobic digesters are designed to not only capture these gases, so they do not escape to the atmosphere, but use them to also offset the use of fossil fuels for energy. This is a win-win for climate change because methane is removed from the atmosphere and fewer fossil fuel is used by renewable biogas-generated electricity, heat or fuel. This is how many biogas systems are carbon negative, meaning they remove more carbon from the atmosphere than they ever put into it. Biogas systems help address not only the climate but also other environmental challenges simultaneously.

Is biogas from manure a clean alternative to fossil fuels?

Biogas is a renewable source of energy that is a direct replacement for non-renewable, carbon-intensive fossil fuels. Without biogas systems, tons of carbon emissions would be released into our air from the waste our society produces, and more fossil fuels would be used to create synthetic fertilizers to grow our crops. Additionally, biogas systems reduce carbon emissions in transportation by at least half compared to fossil fuels. Vehicles fueled by renewable natural gas can reduce carbon emissions six times faster than wind or solar charged battery-electric vehicle.

Does biogas increase GHG emissions?

No. Biogas systems are one of the most effective solutions for reducing GHG emissions, while also addressing our need to manage our waste. Biogas systems protect our air, water, and soil by recycling organic material, like food waste and manure, into renewable energy and soil products, while also reducing GHG emissions. In fact, Biogas systems reduce carbon emissions in transportation by at least half compared to fossil fuels. And vehicles fueled by renewable natural gas can reduce carbon emissions six times faster than wind or solar charged battery-electric vehicle.

What role do livestock play in emitting GHG emissions?

Livestock’s role in greenhouse gases often gets overstated. Livestock contribute to about 6% of emissions worldwide and 4% in the U.S., whereas the majority of GHG emissions are driven by the energy and transportation sectors. Additionally, with genetic and other technological advancements within the livestock industry, the number of animals providing our food products is decreasing, thus reducing GHG emissions and bringing the livestock industry closer to net zero carbon emissions. The use of anaerobic digesters to capture methane that would otherwise be emitted by farms has led to a 30% reduction of California dairy emissions already, and many more can be built increasing that reduction. Further, feed additives could help reduce methane emissions from cows directly. It’s thanks to biogas systems and other environmental solutions that the U.S. dairy industry has set a commitment to achieve carbon neutrality, optimized water usage and improved water quality by 2050.

Renewable Natural Gas

What is renewable natural gas (RNG)?

Unlike conventional natural gas, RNG is not a fossil fuel and does not involve drilling. It is a renewable gas made from biogas that is fully interchangeable with natural gas. No matter how much we reduce waste, as long as we flush toilets, let food spoil, don’t eat onion peels, and raise animals, we will produce the waste that can be turned into biogas and in turn, RNG. Just like conventional gas, RNG can be used to create electricity, powering homes and businesses, and fueling vehicles. RNG is created from biogas, which is mostly methane and carbon dioxide. When the carbon dioxide and some trace elements in the biogas are removed, 95-99% pure methane remains, the same as conventional natural gas, except RNG been renewably produced by recycling organic material.

How is Renewable Natural Gas processed?

Converting biogas to RNG is a multistep process, with different steps to remove different constituents in the biogas to leave almost pure methane. Because biogas consists of mostly methane and carbon dioxide, with traces of other elements, producing RNG mostly consists of removing carbon dioxide. If the biogas has silicone compounds (from cosmetics and cleaning products in wastewater and landfill gas), or sulfur compounds (naturally occurring in our food waste and manure), those are removed as well. After the RNG is processed, it becomes interchangeable with traditional pipeline quality natural gas. You cannot tell an RNG molecule from a conventional gas molecule except the RNG was produced from renewable resources. RNG is versatile and can be used and delivered the same as conventional natural gas with a much better environmental footprint.

Can biogas be a replacement for fossil fuels?

Yes, biogas can replace any uses of conventional natural gas, a fossil fuel, and can help reduce dependency on natural resources. Methane is the principal gas in biogas, which is also the main component of natural gas. Therefore, biogas can replace natural gas in a variety of settings such as cooking, heating, steam production, electrical generation, vehicular fuel, and as a pipeline gas. In addition, when digested material is produced from a biogas system and used as a fertilizer, it replaces more fossil fuel since fossil fuel is used to make and transport all the chemical fertilizers used for agriculture and gardening.

Are there different forms of RNG?

RNG can be either compressed or liquefied. Both forms are used for transportation fuel.

Is RNG carbon free?

RNG can have many different carbon intensities depending on what waste resources it’s made from, how far it is transported, where it’s used, and how it is used. At worse, on a lifecycle basis, RNG produces half the carbon emissions of conventional natural gas. At best, it can remove 6-7 times more carbon emissions from the atmosphere than the use of natural gas and 6 times more than wind and solar used to power electric vehicles. That’s because emissions can be reduced by recycling waste that would otherwise emit methane emissions, and also by displacing fossil fuels in many ways.

What are the benefits of using RNG?

RNG can be used interchangeably with natural gas for heating, electricity, and the production of quality biomethane and transportation fuel. It can be injected into existing natural gas grids and used as a substitute for conventional natural gas. RNG has the potential to replace at least 10 percent of the natural gas being used in the United States and in some cases, gas utilities can use RNG to help them reach net zero carbon goals. The use of RNG reduces greenhouse gas emissions and increases domestic energy production while improving waste management systems.


Myths and Facts

Do biogas systems make farms larger?

There is no evidence that building biogas systems encourages larger farms. In fact, the total number of farms and farm animals has been slowly declining for more than 30 years. It is not economical for farmers to raise animals solely for manure production or to grow more crops to increase waste for biogas systems.

Expanding farms and herd sizes requires years of planning. The decision to increase a farm’s size has been, and continues to be, driven by food prices, or the consolidation of farms driven by the same factors. Tight farm margins and the low prices for many food products, which are primarily driven by the price consumers are willing to pay, are what cause farms to expand. Factors outside of farmers’ control, such as weather, the markets, rising input prices, and other fluctuations, make farming a tough business that requires thoughtful planning.

Biogas systems reduce air emissions and protect the water and soil on farms of all sizes. Some developers may be especially interested in larger farms because of the greater opportunities for carbon emissions reductions and increased profits. However, over 8,000 U.S. farms could benefit from a biogas system but don’t currently have one, and the majority of those are medium and small sized operations.

A biogas system has no effect on how many animals live on a farm or animal husbandry practices. Biogas systems lower greenhouse gas emissions, reduce odor, offer opportunities to improve soil health and keep nutrients from entering nearby waterways, among other benefits.

Two recent articles from the University of California Davis addressed whether manure subsidies are causing farmers to milk more cows in California and the value of methane from cow manure.

Do methane digesters cause greenhouse gases emissions and pollutants?

The limited carbon emissions produced by methane digesters are vastly outweighed by the significant emissions they reduce in almost all cases. Biogas systems protect air, water and soil by recycling organic material, like food waste and manure, into renewable energy and soil products. When not recycled, these organic materials release methane into the atmosphere, which is significantly more harmful to the environment than the negligible carbon dioxide emissions from methane digesters.

In transportation, biogas systems reduce carbon emissions by at least half compared to fossil fuels. Vehicles fueled by renewable natural gas can reduce carbon emissions six times faster than battery-electric vehicles charged by wind or solar.

The total amount of organic material produced in the U.S. includes 66.5 million tons of food waste, 11 trillion gallons of wastewater and manure, and agricultural waste from 8 billion cows, turkeys, chickens and pigs. If this waste is not recycled using a biogas system, it will continue to produce carbon emissions.

Do biogas system tanks cause environmental damage when they rupture?

Digester leaks are exceptionally rare because most of the 2,000 biogas systems in the U.S. are designed with safety mechanisms to protect those working on them and the environment. Biogas systems have physical retaining systems, such as ditches and culverts, that would physically contain a spill on the property, so material can be properly handled, and repairs can be made without material escaping.

Are there other organic waste management options?

Biogas systems and composting are the only solutions for waste management; other much less environmentally friendly disposal methods are landfills or incinerators. Unlike other options, biogas and compost systems protect the climate, air, water and soil by recycling organic material, like food waste and manure, into renewable energy and soil products while also reducing GHG emissions.

Do methane leakages make RNG (renewable natural gas) production climate intensive?

Since biogas systems prevent methane that would have otherwise been emitted if there were no biogas system, any methane loss less than 100% is an improvement to the climate. That said, leakage rates for anaerobic digesters have been found in peer-reviewed literature to be in the range of 0.4-14.9%. This correlates to 99.6-85.1% of methane emissions prevented. The California Air Resources Board in their GREET 3.0 model uses a default 2% leak rate.

Do biogas systems perpetuate the fossil natural gas industry?

Every molecule of renewable natural gas (RNG) produced and utilized is a molecule of methane emission avoided. If organic material, such as food waste, manure and wastewater sludge, is not recycled in a biogas or compost system, it will emit methane emissions into the atmosphere. Organic material must be recycled to reduce greenhouse gases.

The California Air Resources Board (CARB), a state government agency that uses the Argonne National Lab GREET model for carbon emissions, assumes a 2% leakage rate for biogas projects. By comparison, this is significantly less than the 5% electricity transmission losses reported by the U.S. Energy Information Administration (source).

According to CARB, the lowest carbon energy for transportation is from biogas produced by anaerobic digesters, then turned into RNG or electricity. The carbon intensity of each project is based on the entire lifecycle of renewable energy production and use, determined using the Argonne National Laboratory GREET model. The carbon intensity score for each project is approved by both third-party experts and CARB.

Is it worth investing in natural gas pipeline infrastructure in the U.S.?

While biogas may not completely replace natural gas, it does significantly reduce landfill waste, which natural gas and renewable electricity cannot do. Biogas systems offer giant opportunity in the U.S., which throws away 30-40% of all food. Investing in natural gas pipelines will aid the journey toward net-zero by preparing existing infrastructure for future clean fuels and, in the meantime, reducing harmful methane leaks from natural gas, according to a Columbia University report (source).

For some gas utilities, adding a percentage of negative carbon RNG can bring the utility’s carbon emissions to zero. Washington Gas plans to use RNG for one-third of its net-zero by 2050 goal (source), and SoCalGas announced aspiration to achieve net-zero greenhouse gas emissions in operations and delivery of energy by 2045 (source).


At this time, natural gas use is still required for the resiliency of the energy system and remains the most efficient way to produce large amounts of heat. In many Northern states, the electric grid simply cannot meet the heating needs during the entire winter.

Recycling of organic material with biogas systems is one of only two ways to reduce the enormous volumes of organic material produced annually in the U.S., including 66.5 million tons of food waste, 11 trillion gallons of wastewater, and manure and agricultural waste from 8 billion cows, turkeys, chickens and pigs.