Generating RNG from Dairy Cow Manure

Gevo expects to generate renewable natural gas, or RNG, by collecting manure from dairy farms. This concept fits in with our philosophy of addition by subtraction: We simultaneously seek to reduce greenhouse gas emissions (GHGs) as we figure out ways to generate usable renewable energy from the process.

According to Our World In Data, food production accounts for 25 to 35 percent of global GHGs, with more than 7 billion tons of carbon dioxide of that amount attributed to livestock and fish farms. Livestock contributes emissions to this measurement in a few different ways:

  • Enteric fermentation is gas produced by microbes in the digestive system of livestock animals, chiefly methane. It is emitted through belching and flatulence, and this usually increases when the animals are fed starchy food.
  • Manure management contributes to GHGs. As manure is left to decompose, it releases greenhouse gases, including methane.
  • Management of pastureland is also a factor, as the ground emits carbon dioxide.

Renewable Natural Gas Can Help Reduce Greenhouse Gas Emissions

Renewable natural gas is expected to be a key renewable energy source for transportation needs. RNG-fueled vehicles are estimated to result in up to 95 percent lower emissions than those fueled by gasoline or diesel on a lifecycle basis, according to a US Department of Energy study RNG is proving to be a key fuel in the energy transition.

Download the Argonne National Laboratory Frequently Asked Questions about Renewable Natural Gas for Transportation here.

Capturing Emissions on the Farm

By installing anaerobic digesters on dairy farms, we will capture vast quantities of manure generated in an enclosed structure. Using complex microbial communities to break down the manure, the digesters capture the methane gas that would otherwise go into the atmosphere. This biogas is an energy source that comes from natural processes that have captured carbon from the atmosphere.

Cows and other livestock eat plants. Any corn, hay, grass, or other plant matter—which may include Gevo’s high-protein animal feed—that the animal consumed has drawn carbon dioxide from the air through photosynthesis into plant matter. As the animal processes the feed to get its own energy to move around, produce milk, etc., the carbon that the plants took from the atmosphere goes back into the atmosphere. This carbon system adds critical protein and nutrients to the food chain.

Livestock, however, doesn’t use up all the nutrients contained in its feed sources. Many important nutrients remain in the manure. These nutrients persist in the remaining manure after it comes out of the digester. This manure can be spread on farm fields to replenish the soil, obviating the need for synthetic inputs, saving the farmer money while also eliminating still another source of pollution.

Adding to the Food Chain while Reducing GHGs

Nutrition experts and dietitians tell us, protein is a key factor in human nutrition. Gevo uses sustainably grown, No.2 yellow dent corn to produce high protein animal feed for aquaculture and pet food, as an example. The nutrients in the corn are concentrated in those animal feeds, through that process there is a residual starch that is removed. This starch has very little nutrient value and would require excess energy, and inherently fossil fuel emissions to purify it for human consumption. Gevo further processes the residual starch into hydrocarbons like jet fuel and renewable gasoline. This is done with Gevo’s proprietary process, which has been piloted in Luverne, MN for years.

It’s this kind of forward-thinking land use, where an acre of farmland produces food and also contributes to clean energy, that will allow the world to achieve net-zero carbon emissions in both agriculture and transportation, while continuing to support the nutrient needs of people globally.

RNG Creates Clean Energy and the Promise of Marketable Sustainability

Sustainability is coming, and it will become an important factor in the decisions that are made every day up and down the supply chain.

Of course, the RNG itself has sustainability value, and some programs will readily add any additional factors that show reduced GHGs. Two examples are California’s Low Carbon Fuel Standard (“LCFS”) program and the U.S. Environmental Protection Agency’s Renewable Identification Number (“RIN”) program.

Dairy farmers who partner with us and install manure digesters could reap benefits from RNG production, since this added factor would be expected to improve the farms’ overall sustainability. At the very least these digesters will lay the groundwork for more efficient recycling of nutrients and better soil health.

Some think that farms who install digesters will have a more appealing product. If sustainability is tracked like we think it will be, and using the Argonne GREET model or a similar model that tracks carbon intensity and greenhouse gas emissions over the entire lifecycle of products including their supply chain, then farms that reduce the lifecycle inventory of their products can pass that sustainability on to their customers.

In the case of a dairy farm, the milk from a farm that uses manure digestion to reduce its carbon intensity could be more valuable to a cheese or ice cream manufacturer who wants to sell sustainably sourced and produced products to its customers. The farmer gets a higher price for milk output per gallon because it has the added sustainability value that has been verified.

How Gevo Uses Clean Energy

Every Btu of RNG and every gallon of energy-dense liquids, including sustainable aviation and renewable gasoline, and even every pound of green hydrogen, that Gevo expects to sell into the market could eliminate of the equivalent of the fossil fuels burned. Gevo is developing plans to use biogas, utilizing an on-site anerobic digester (like a water treatment plant) to heat or otherwise power its production facility. Every Btu or Watt of energy used in our production that can be supplied by renewable energy sources is one more factor that reduces our carbon intensity. This is why Gevo has chosen to utilize clean sources for both the thermal demands of the plant (biogas) and the electrical demands (wind). Our lifecycle analysis will show one piece of our sustainability metrics, and could then be shared with our customers, who benefit from enhanced sustainability. Our energy-dense liquids and RNG products are being designed to store renewable energy in ways that it can be readily adapted to today’s vehicles, aircraft, boilers, furnaces, and fuel transportation and storage infrastructure. The goal is to achieve net-zero carbon emissions. Once there, we will pursue negative carbon emissions, to help reduce the effects of GHGs in the atmosphere and to draw carbon back from the atmosphere into the ground where Mother Nature put it.