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Biogas Basics Biogas has the capability to fuel the more than 100,000 natural gas vehicles in the United States and roughly 11.2 million vehicles worldwide. In fact, 10% to 15% of current fossil natural gas use could potentially be displaced by 2025 if biogas was produced from current available agricultural, landfill, and industrial organic waste sources. Biogas used in natural gas vehicles is perfect for high-mileage fleets, such as buses, taxis, and the trucking industry.

What is biogas?

Biogas—also known as biomenthane, swamp gas, landfill gas, or digester gas—is the gaseous product of anaerobic digestion (decomposition without oxygen) of organic matter. When processed to purity standards, biogas is called renewable natural gas (RNG) and can substitute for natural gas as a vehicle fuel.

Biogas is usually 50% to 80% methane and 20% to 50% carbon dioxide with traces of gases such as hydrogen, carbon monoxide, and nitrogen. In contrast, natural gas is usually more than 70% methane with most of the rest being other hydrocarbons (such as propane and butane) and traces of carbon dioxide and other contaminants. When oxygen is introduced to carbon monoxide, hydrogen, and methane, it oxidizes or combusts.

How is biogas produced and distributed?

Biogas is a product of decomposing organic matter, such as sewage, animal byproducts, and agricultural, industrial, and municipal solid waste. Biogas must be upgraded to a purity standard to fuel vehicles or to be distributed via the existing natural gas grid.

Refining biogas means increasing the proportion of methane and decreasing the amount of carbon dioxide and contaminants through absorption, adsorption, membrane separation, or cryogenic separation.

Landfills are the third-largest source of

human-related methane emissions in the United States. Methane can be captured from landfills and used to produce biogas. Methane gas collection is practical for landfills at least 40 feet deep with at least 1 million tons of waste.

Animal manure is the second most popular feedstock for biogas. Recovery systems at livestock operations can produce renewable energy in cost-effective ways. Animal manure can be collected and delivered to an anaerobic digester to stabilize and optimize methane production. The resulting biogas can be used to fuel NGVs. One cow can produce enough manure each day to create three-kilowatt hours of electricity. The U.S. Environmental Protection Agency (EPA) estimates 8,200 U.S. dairy and swine operations could support biogas recovery systems with the potential to generate more than 13 million megawatt-hours and displace about 1,670 megawatts of fossil fuel-fired generation collectively per year.

Biogas recovery systems are also feasible at some poultry operations.

RNG can be distributed via existing natural gas distribution routes. Because these technologies are not developed and tested fully

Biogas is produced using an anaerobic digester (decomposition without oxygen), such as the one pictured in Janesville, Wisconsin. yet, distributing renewable natural gas via the pipeline grid is not common practice.

How is biogas used?

Biogas can be used to generate electricity, fuel vehicles, and heat homes. To produce electricity, biogas can be fed directly into a gas-fired combustion turbine, which in turn powers a turbine generator. To be used in vehicles, the gas must be refined and can then be used in NGVs. Additionally, biogas can be compressed into liquid natural gas (LNG) and used to heat homes and power compressed NGVs.

Benefits of biogas Biogas can be an alternative to conventional transportation fuels. The benefits of biogas are similar to the benefits of natural gas.

Additional benefits include: • Increased Energy Security—Biogas offsets non-renewable resources, such as coal, oil, and fossil fuel-derived natural gas. Producing biogas creates U.S. jobs and benefits local economies.

• Fewer Emissions—Biogas reduces emissions by preventing methane release in the atmosphere. Methane is 21 times stronger than carbon dioxide as a greenhouse gas.

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Wisconsin Clean Cities · www.wicleancities.org · Page 2 • Better Economics—Biogas can reduce the cost of complying with EPA combustion requirements for landfill gas.

• Cleaner Environment—Producing biogas through anaerobic digestion reduces landfill waste and odors, produces nutrient-rich liquid fertilizer, and requires less land than aerobic composting.

Is biogas safe for use in vehicles?

Yes. Biogas is used in natural gas vehicles (NGVs). NGVs meet the same safety standards as gasoline and diesel vehicles and also meet the National Fire Protection Association’s (NFPA) NFPA 52 Vehicular Fuel System Code. Natural gas has a narrow flammability range and, because it is lighter than air, dissipates quickly if released. NGV fuel tanks are strong and extremely puncture resistant.

How do biogas vehicles work?

Biogas vehicles are NGVs, and can operate in one of three modes: dedicated, bi-fuel, or dualfuel. Dedicated NGVs run on only natural gas.

Bi-fuel NGVs can run on either natural gas or gasoline. Dual-fuel vehicles run on natural gas and use diesel for ignition assist. Light-duty vehicles typically operate in dedicated or bi-fuel modes, and heavy-duty vehicles operate in dedicated or dual-fuel modes.

A CNG fuel system transfers high-pressure natural gas from the storage tank to the engine while reducing the pressure of the gas to the operating pressure of the engine’s fuel-management system. The natural gas is injected into the engine intake air the same way gasoline is injected into a gasoline-fueled engine. The engine functions the same way as a gasoline engine: The fuel-air mixture is compressed and ignited by a spark plug and the expanding gases produce rotational forces

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that propel the vehicle.

On the vehicle, natural gas is stored in tanks as CNG, or in some heavy-duty vehicles, as LNG, a more expensive option. The form chosen is often dependent on the range a driver needs. More natural gas can be stored in the tanks as LNG than as CNG.

How do biogas vehicles perform?

Natural gas vehicles are similar to gasoline or diesel vehicles with regard to power, acceleration, and cruising speed. The driving range of NGVs is generally less than that of comparable gasoline and diesel vehicles because, with natural gas, less overall energy content can be stored in the same size tank as the more energy-dense gasoline or diesel fuels. Extra natural gas storage tanks or the use of LNG can help increase range for larger vehicles.

In heavy-duty vehicles, dual-fuel, compressionignited engines are slightly more fuel-efficient than spark-ignited dedicated natural gas engines. However, a dual-fuel engine increases the complexity of the fuel-storage system by requiring storage of both types of fuel.

How much do biogas vehicles cost?

Light-duty NGVs cost $5,000 to $7,000 more than comparable gasoline vehicles, and heavyduty NGVs cost more than their counterparts by $30,000 or more. The price depends on the fuel-tank capacity and whether the vehicle is produced by an OEM or converted to run on natural gas. However, government incentives may be available to offset NGV costs. For more information, visit the AFDC’s Incentives and Laws section at www.afdc.energy.gov.

Due in part to the high octane rating and clean-burning properties of natural gas, some fleets have reduced maintenance and operating

costs for NGVs compared with conventional vehicles.

Who is using biogas in Wisconsin?

Many fleets in Wisconsin are exploring the use of biogas. One example is Dane County, who produces compressed natural gas for their NGVs from the Dane County landfill. The anaerobic digester is one of the first of its kind in Wisconsin. The CNG produced costs 20 cents per gasoline gallon equivalent.

One of Dane County’s new natural gas vehicles being fueled up with their landfill sourced renewable natural gas (biogas).

The county started converting landfill methane into electricity in the mid-2000s and now earns $4.3 million a year from the system. The system is anticipated to produce 100 gallons of CNG each day, enough to fuel many of their newly acquired NGVs through the Wisconsin Clean Transportation Program.

Similarly, the City of Janesville produces biogas from the City’s wastewater treatment plant and refines it into CNG for use in city vehicles. Janesville is saving thousands of dollars in fuel costs annually since the cost of the gas is less than one dollar per gallon. The project was supported by a $125,000 grant from the State of Wisconsin, and was a component of a comprehensive upgrade and expansion of the City’s wastewater treatment plant.

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