by Christina Nagy-McKenna, Enerdynamics Instructor
Most of us think of natural gas as a reliable, plentiful fossil fuel. Less discussed is its renewable equivalent: biomethane, a biogas that is the result of the decomposition of organic matter. Once processed, this 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 waste water treatment plants, renewable natural gas (RNG) is being used to produce electricity and to fuel large trash and recycling vehicles. Use of RNG in the clean transportation section has strong potential to help states meet their federal and state fuel standards for reduced petroleum product use.
There are three major sources of biogas in the United States:
- 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 they then cover 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.
Depending on whether the gas goes directly to a power plant, a pipeline, or if it will be made into a transportation fuel, it is cleaned to the appropriate specifications.
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.
One of the most successful RNG projects in the U.S. can be found at the Waste Management Inc. Altamont Landfill in Livermore, Calif. A joint venture between WMI and Linde BOC, the project can consume more than 2,600 standard cubic feet per minute (scfm) of landfill gas and has an operational capacity of 13,000 LNG gallons per day. This LNG displaces more than 2.8 million gallons of diesel fuel per year. According to Waste Management, the project achieved a capture rate of 93 percent; it produces enough LNG to fuel 300 of its 491 LNG vehicles, which collect waste and recycling.
The Altamont project gives us a glimpse into what is possible in recovering landfill gasses and processing them into RNG. 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.
Thus, the potential for improvement and expansion is great. The time has come to acknowledge RNG as a viable form of natural gas and transportation fuel that may be well-suited to help reduce greenhouse gas emissions and meet renewable fuel standards goals.
Footnotes and references:
 Altamont Landfill Gas Purification, Testing, and Monitoring, Gas Technology Institute for the California Energy Commission, October 2013, page 2.
 Renewable Natural Gas (Biomethane) Production, U.S. Department of Energy – Energy Efficiency and Renewable Energy Alternatives Fuels Data Center, May 10, 2016, page 1.
Altamont Landfill Gas Purification, Testing and Monitoring, Final Project Report, Gas Technology Institute for the California Energy Commission, October 2013.
“Biogas/Biomethane for Use as a Transportation Fuel,” European Biofuel Technology Platform web site www.biofuelstp.eu, September 9, 2016.
“Biomass Explained,” U.S. Energy Information Administration, November 12, 2015.
Biomethane, NGV America web site www.ngvamerica.org., 2014 Inc., 2011.
Jaffe, Amy Meyers, The Feasibility of Renewable Natural Gas as a Large Scale, Low Carbon Substitute, UC Davis Sustainable Transportation Energy Pathways, Institute of Transportation Studies for the California Air Resources Board and the California Environmental Protection Agency, June 2016.
Renewable Natural Gas (Biomethane) Production, U.S. Department of Energy – Energy Efficiency and Renewable Energy Alternatives Fuels Data Center, May 10, 2016.
Resources – Education, The Coalition for Renewable Natural Gas website, www.rngcoalition.com.