What is Renewable Natural Gas?

From Scott Carlberg

Turns out there are two kinds of natural gas. One is from the ground. Petroleum exploration and production companies drill and find it in rock formations. The other is from, well, something else. It is called renewable natural gas (RNG) and often starts with waste from animals, even people sometimes.

RNG is in the Carolinas, too.

Some definitions to get us started.


Methane is a significant and plentiful fuel which is the principal component of natural gas. Burning one molecule of methane in the presence of oxygen releases one molecule of CO2 (carbon dioxide) and two molecules of H2O (water). However, because it is a gas and not a liquid or solid, methane is difficult to transport from the areas that produce it to the areas that consume it. Methane is a greenhouse gas.” (Source)

The Anaerobic Digestion Process. Visual courtesy of Environmental and Energy Study Institute (EESI) under a creative commons use.

Anaerobic digestion: 

“Anaerobic digestion is a series of biological processes in which microorganisms break down biodegradable material in the absence of oxygen. One of the end products is biogas, which is combusted to generate electricity and heat, or can be processed into renewable natural gas and transportation fuels. A range of anaerobic digestion technologies are converting livestock manure, municipal wastewater solids, food waste, high strength industrial wastewater and residuals, fats, oils and grease, and various other organic waste streams into biogas.” (Source)

Renewable Natural Gas: 

“RNG, also known as biomethane, is natural gas produced by the decomposition of organic matter under anaerobic (oxygen-free) conditions. The gas is captured and then purified to remove components such as water, carbon dioxide, and hydrogen sulfide. The major sources of RNG are landfills, animal manure, and solid waste extracted during wastewater treatment. The term renewable is used to describe this natural gas because it is derived from waste that is continuously produced by present-day activities. These waste sources naturally produce methane as they decompose, so RNG production captures methane that would otherwise escape into the atmosphere.” (Source)

RNG’s attractiveness is that it takes the cost of waste management and makes it a usable product or revenue option for the agriculture industry. Greenhouse gas emissions are reduced, fuel is made that can be used for transportation, and it can create employment, too.

This facility in Duplin County, N.C., gathers methane gas from five local hog farms and converts it to pipeline-quality natural gas. The gas is transported to a Duke Energy gas power plant where it is part of the fuel mix. It is the first time Duke Energy has used renewable natural gas from in-state farms at its power plants. (PRNewsfoto/Duke Energy)

Is there RNG in the Carolinas? Yes. Just under half of Smithfield Food’s carbon footprint is from methane emissions resulting from hog manure on company and contract farms. Some of those are using hog manure to make usable natural gas. From Smithfield: “Our newest endeavor is in Duplin County, North Carolina, where anaerobic waste digesters are now capturing biogas from some 60,000 hogs on five Smithfield contract farms. We view this project as a first step in what can serve as a model for many of our North Carolina farms to participate in manure-to-energy projects going forward.” 

Duke Energy and Dominion both have North Carolina ventures in RNG. A Duke Energy power plant is using renewable natural gas from North Carolina-based hog farms to produce electricity – the first application of the technology from in-state farms. Dominion Energy and Smithfield Foods  announced their first projects in North Carolina with a joint venture, Align Renewable Natural Gas (RNG), to capture methane emissions from hog farms and convert them into renewable energy for residential home heating and power for local businesses. (Source)

More is on the way. The North Carolina Utilities Commission approved Catawba Biogas LLC, a proposed poultry-waste biogas plant in Anson County, for a pilot program that will allow the facility to inject RNG to pipelines operated by Piedmont Natural Gas, a subsidiary of Duke Energy. (Source)

Finally, because the public often hear of fracking and natural gas in the same breath, some people ask if RNG involves fracking. It does not. Fracking is done to break open migration pathways for natural gas within rock formations. Since RNG comes from animals and plants, not rocks, there is no fracking involved.

Watch for more renewable natural gas news. It has a future. Several fleet operators, like UPS and Republic Services, have noted the way they are adopting alternative fuel vehicles, and agricultural applications appear to be growing. We’ll feature some of those uses soon.