Renewable natural gas (RNG or biogas) can be a substitute for pipeline quality gas and gas used for transportation fuel either as compressed natural gas (CNG) or liquefied natural gas (LNG). By reclaiming methane from landfills, livestock operations, and wastewater treatment plants, RNG is being used to produce electricity and to fuel large trash and recycling vehicles. Use of RNG in the clean transportation sector has strong potential to help states meet their federal and state fuel standards for reduced petroleum product use. RNG is derived from organic waste materials as well as from degradable carbon sources such as wood, paper and cardboard. Typical sources include:
- Landfills: At landfill sites, methane is extracted, collected, and then processed until it is clean enough for use.
- Livestock operations: At livestock facilities like dairies and pig farms, farmers may collect manure and place it in an anaerobic digester that produces methane, or they may maintain a lagoon that contains manure, which is then covered to capture the methane.
- Wastewater treatment plants: At these treatment plants, biogas is recovered during the digestion of solid materials that are removed from wastewater treatment. Once biogas is recovered at such facilities, it is processed until water, carbon dioxide, hydrogen sulfide, and other impurities are removed.
The gas is then cleaned to the appropriate specifications which vary depending on the ulimtate destination and use of the gas (e.g., to a power plant for electric generation, into a pipeline where it is mixed with other sources of natural gas, or for use as a transportation fuel).
While it is helpful that RNG can be used as a substitute for traditional natural gas, it is also valuable because it meets the requirements as an advanced biofuel under the U.S. Renewable Fuel Standard (RFS). The RFS was authorized by Congress as part of the Energy Policy Act of 2005 and then expanded under the Energy Independence and Security Act of 2007. Its goal is to reduce greenhouse gas emissions and create a more robust renewable fuel sector while reducing U.S. reliance on imported oil.
RNG from plant sources is considered a carbon-neutral fuel because it comes from organic sources that once absorbed carbon dioxide from the atmosphere during photosynthesis (as opposed to fossil fuels which release carbon that previously was trapped underground). RNG has even greater benefits when it's produced from organic waste that would otherwise decay and create methane emissions. By capturing more greenhouses gases than it emits, this RNG reduces man-made carbon emissions into the atmosphere.
As of March 2015, there were close to 645 operational projects at landfills around the country. Most, however, convert biogas into electricity rather than using it as transportation fuel. As of January 2015, there were also 247 anaerobic digesters operating at commercial livestock facilities nationwide. Lastly, there are approximately 1,500 anaerobic digesters being used in the U.S. at 16,000 wastewater treatment plants.