Renewable Natural Gas from cows

I bet you guys thought we’d never be talking about cow manure here at Schaper Energy….well, you were wrong!

There’s plenty of talk about natural gas and its usability for heating. A recent popular story featured the Russian natural gas pipeline, Nord Stream 2, that will be utilized to distribute gas to Germany under the Baltic sea, doubling the Russian gas supply to Germany. U.S. officials oppose the project, stating it would further increase Europe’s reliance on Russian gas and make regional infrastructure vulnerable to interruption, but what are the alternatives to importing or extracting natural gas? 

One of the promising answers comes in the form of Renewable Natural Gas (or ‘RNG’). It has the same properties as natural gas except that it is made from waste collected from livestock farms, landfills and products of food and beverage. In contrast, natural gas is extracted from the earth and is composed of organic matter that has been cooked in the Earth’s crust for millions of years.

The great thing about renewable natural gas is that it can be transported through the same pipelines that transport other gases, so in effect it is an identical substitute only produced through a different method. Renewable natural gas can also be converted to Liquified Natural Gas (LNG) or used directly as a fuel in the transportation sector.

How is Renewable Natural Gas Produced?

Organic waste used for production of RNG
Source: EPA RNG

Renewable gas is produced from organic waste as a byproduct of food or beverage production, cow manure in the dairy industry or other organic sources. This waste is treated with bacteria and produces biogas which later is converted into biomethane.

Biogas is mainly produced through a process called Anaerobic Digestion, which is a series of biological processes that use different types of bacteria to break down organic materials into biogas, primarily methane. Depending on the bacteria used, this process lasts 30-60 days and requires temperatures between 90°F and 140°F. Anaerobic digestion is conducted in the absence of oxygen, as the name suggests. The end product is biogas, which is a mix of methane (60-70%) and carbon dioxide (30-40%). More about this process can be found in this short pdf.

Anaerobic digestion process
Process of Anaerobic Digestion (AD)

The biogas is then distilled by removing water vapor, carbon dioxide, hydrogen sulfide and other impurities to become pure biomethane, which is indistinguishable from the methane found in typical natural gas.

Aside from energy applications, this process is also beneficial because it prevents unnecessary extraction activities and keeps the environment clean from organic waste. Air quality is improved with a reduction in waste evaporation and water is protected from toxic waste, pathogens and underground water contamination.

Where Can RNG Production be Used Best?

Renewable gas can be used in many fields; however, dairy farming and transportation seem to be ideal choices due to the amount of the greenhouse gases (GHG) that both industries generate.

In virtually all industrial activities, GHG emissions have been lowered, with exception of dairy farming and transportation. Despite the fact that new cars use cleaner fuel, every year more and more transport vehicles are produced and driven causing the amount of GHG to continually rise. 

California has tried to address these two problems through regulation and incentives. The state is home to the largest dairy industry in the US, with over 1.7 million cows producing milk and 1,300 producing dairies. This amounts to around 18.5 percent of all milk and dairy products consumed in the United States. 

Emissions from the California dairy industry increased by 23.8% between 2000 and 2016, which is a huge figure. On the other hand, transportation carbon emissions have also gone up every year since 2013.

California has over 25.5 million cars and 5.7 million trucks on the roads. The state’s transportation sector is responsible for about 41% of the state’s inventory of 429.4 million metric tonnes of carbon dioxide equivalent (2016 Inventory).

California has tried to address this issue by passing AB 32, the California Global Warming Solutions Act of 2006. This act required California to reduce its GHG emissions to 1990 levels by 2020, a reduction of approximately 15 percent below emissions expected under a “business as usual” scenario. This meant implementing new technologies and processes to help lower GHG emissions over a 20 years period. 

The regulation has yielded results, as shown by the period from 2000 to 2016 which demonstrated a general reduction of 9% in greenhouse gas emissions. This was accomplished in large part by establishing the Low Carbon Fuel Standard (LCFS) program and the Cap-and-Trade program. 

The Low-Carbon Fuel Standard (LCFS) is a set of rules enacted to reduce carbon intensity in transportation fuels when compared to conventional petroleum fuels, such as gasoline and diesel. The most common low-carbon fuels are liquid biofuels and natural gas from sources outside of extractive industries.. The LCFS was recently updated with new targets to reduce carbon footprint by 20% by the year 2030, the previous target being a 10% reduction by the year 2020. Carbon reduction is measured by average carbon intensity (CI, in gCO2e/MJ) of transportation fuels that are used. Reduction in CI is reduction in greenhouse gases GHG. The plan for reducing CI/GHG by 20% till 2030 can be seen on the image below.

Performance of California’s LCFS (2011-2020)
Performance of California’s LCFS (2011-2020)

Renewable natural gas, particularly the type made from cow manure, prevents methane emission into the atmosphere by capturing the digested gas and converting it into a fuel with a very low carbon footprint; in fact, it’s actually carbon negative (it removes carbon from the atmosphere). By using manure RNG as a transportation fuel, you can actually earn LCFS credits. EcoEngineers estimated in their December 2020 discussion with Iowa State University and IEDA that LCFS credits can lead to realized prices of up to ~$80/mmbtu for cow gas RNG projects, 18.7x higher than the prevailing trading price of Henry Hub natural gas as of this writing.

The Cap-and-Trade program follows the same logic as LCFS, only it’s targeted for legal entities in the industry. Regulated entities in California pay a fee to the state for their GHG emissions. This revenue funds the incentives for non-regulated sectors, like agriculture, to voluntarily reduce emissions. These programs serve as a powerful incentive for dairies to install digesters for Anaerobic Digestion. This allows them to produce their own RNG, which can later be sold or traded as excess emission credits with entities that pollute more.

It is estimated that at least 2,000 cows are needed to make the digester viable, which would be a covered lagoon digester producing gas for pipeline injection. Estimates for this type of facility involve 2,500 cows and 3 million dollars, with the cost of installation varying greatly based on the dairy’s location, size, manure management and surrounding infrastructure.

Having bigger farms with more cows reduces the cost; each additional 1,000 cows reduces the cost per cow of digester projects by 15-20%.This particular estimation is only applicable to California, as costs in other states can vary.

If we take the US as a whole, there are 32.4 million beef cows and 9.3 million dairy cows. By some estimates, cow power alone has the potential to make up 20.5% of all current use of natural gas in transportation. If we add the other sources of RNG like landfill waste, wastewater treatment plants, and other types of manure waste such as poultry and swine, this number can go much higher.


Renewable natural gas holds big promise for the future. Although it’s still more expensive than fossil-based natural gas, if we follow the trend of an expanding dairy industry and organic waste disposal, the need for a system that will convert greenhouse emissions into something useful becomes obvious. Connecting these industries with the transportation sector via incentives creates a wider system where these energies could be recycled and used for transportation, heating, generating electricity and other needs. Over time, RNG processes could become less expensive and more available, making renewable natural gas a viable alternative to regular natural gas. 

Andrew Schaper is a professional engineer and principal of Schaper Energy Consulting.  His practice focuses on advisory in oil and gas, sustainable energy and carbon strategies.

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