March 25, 2013

Renewable Natural Gas: Fueling Sustainable Transportation

Part 1: What is Renewable Natural Gas?

By Jonathan Morissette and Karen Graham 
Sustainable Energy Futures at Westport Innovations

This is the first in a series of blog posts that will highlight the market and environmental potential of renewable natural gas (RNG). Check back over the next six weeks as we explore the issues and opportunities for RNG in the transportation sector.

What is Renewable Natural Gas?

Renewable natural gas (RNG) is pipeline quality gas that can be used like fossil natural gas but is produced from what are called biogas and biomass feedstock sources, the technical term for any renewable, biological material such as plant matter or animal wastes. It can be a substitute for, or be blended with conventional natural gas for use in vehicle engines.

RNG is produced from a variety of sources, including:
  • Landfill gas 
  • Solid waste 
  • Municipal waste water 
  • Agricultural manure 
  • Forestry waste 
  • Energy crops 
RNG is produced in two ways: anaerobic digestion and thermal gasification.

Anaerobic digestion is the most commonly used and well-developed method. It requires only a low-oxygen environment for the organic matter to breakdown naturally by bacteria, and the equipment and process is commercially available.[i] This technique is best suited to using landfill and agricultural waste. The first biogas digester was built over 150 years ago, and the technology’s simplicity makes it appealing for a range of end uses who want alternative fuels, including transportation use. It’s in commercial use for transportation in parts of Europe, led by Sweden and Germany, and in the U.S., mainly California.

Thermal gasification is a mature and well-established industrial process developed to convert coal or organic matter into gaseous products by the application of high temperatures in oxygen controlled environments. Thermal gasification will help use promising second generation energy crops like poplar or willow trees and switchgrass. While thermal gasification of coal is a mature technology, thermal gasification of biomass into RNG is still pre-commercial with successful demonstration plants in Europe, and commercial scale implementation expected by 2020.[ii] 

The end product of organic matter breakdown is biogas, which is naturally discharged into the atmosphere where it contributes to smog and climate change (methane, carbon dioxide and nitrous oxide). Landfill sites are ideal for capturing and using biogas generated from decomposing waste. Many cities and smaller communities have developed projects to capture, clean and upgrade the biogas from their landfill sites. They use the RNG in their own applications (such as garbage pickup vehicles) or supply it to the pipeline grid. A benefit of RNG for transportation is that it turns waste (such as manure and food scraps) into usable vehicle fuel. By capturing these natural emissions before they enter the atmosphere, the air quality around the collection site is immediately improved and greenhouse gases (GHG) are reduced. Using RNG for transportation helps to reduce GHG emissions as the naturally-produced methane is converted to carbon dioxide, a less potent greenhouse gas.[iii]

Once produced and refined to pipeline quality RNG, this resource can serve any of the end-use applications that fossil natural gas does today. It can be compressed and dispensed as vehicle fuel, injected into pipeline networks, used to manufacture plastics or fertilizer, or liquefied for long-distance and heavy-duty transportation. Because RNG is interchangeable with fossil natural gas, the two fuels can be blended together in a range of proportions at either the pipeline or the pump. As long as RNG is pipeline (and vehicle engine) quality, it can be used wherever the market or regulatory environment supports it for transportation. In Sweden in 2011, 43.9 percent of all produced biogas was used as transport fuel, and in Germany some fueling stations offer 100 percent RNG for natural gas vehicles.[iv],[v]

Current estimates of RNG’s potential show the significant contribution it can make to fuel security and sustainability even in the near term. In the U.S. this renewable resource has been estimated at 4.8 trillion cubic feet, around 20 percent of total current U.S. natural gas consumption.[vi] Within the European Union, production is expected to reach 48bcm by 2020 with the potential for 200 bcm.[vii] 

[i] Brad Rutledge, “California Biogas Industry Assessment: White Paper,” WestStart-Calstart (April 2005): 
[ii] Salim Abboud et al.,“Potential Production of Methane from Canadian Wastes,” Canadian Gas Association (October 2010): ARCFINALReport-Oct72010.pdf. 
[iii] United States Environmental Protection Agency, “Landfill Methane Outreach Program—Benefits of Landfill Gas Energy,” last updated September 2012, accessed March 2013:
[iv] Gabriela Vanciu and Nina Miresashvili, “Biogas cars in Sweden: An emerging market,” Jönköping University (May 2012).
[v] NGV Journal, “Germany: 18 additional CNG filling stations now provide 100% biomethane,” last updated December 18, 2012, last accessed March 22, 2013.
[vi] National Petroleum Council, “Renewable Natural Gas for Transportation: An Overview of the Feedstock Capacity, Economics, and GHG Emission Reduction Benefits of RNG as a Low-Carbon Fuel,” (March 2012).
[vii] Floris van Foreest, “Perspectives for Biogas in Europe,” Oxford Institute for Energy Studies Working Paper series (December 2012).


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