What is the Anaerobic Digester, and How Does It Relate to Sustainable Farming and Products?

Farms can go green by using anaerobic digesters to process manure into renewable natural gas (RNG). Oak Ridge Dairy built an anaerobic digester, which contributes to cleaner air and reduces the “farm smell,” too. We clean the manure from the barns daily and deposit it into a big tank – the anaerobic digester. From there, the tank and nature start working.

Let’s get into why farms can benefit from an anaerobic digester!

Anaerobic Digester Process

As new technology becomes available, our waste management practices become more sustainable. Instead of renewable natural gas emissions going into the air, we can provide enough RNG to power hundreds of homes with our dairy farms’ digester.

The manure goes through five digesting stages before turning into renewables. Once complete, you have natural gas (methane) and solids that can be used as fertilizer for crops. We have a digester on the farm to handle all the manure our cows produce.

Step 1: Aerobic Decomposition

In the first stage, aerobic bacteria create a chemical reaction with moisture to break down organic molecules, including carbohydrates. During this process, the temperature of the manure increases to about 158 degrees Fahrenheit. This chemical reaction produces carbon dioxide and water vapor as the bacteria consumes any available oxygen. Once the bacteria ingests the oxygen, it triggers the next stage.

Step 2: Anaerobic Acidogenesis

The microbes that cause hydrolysis in this stage are poisoned by oxygen. These microbes can flourish once the oxygen has been depleted. Hydrolysis – a form of fermentation – produces hydrogen, carbon dioxide, water vapor, ammonia, nitrogen, and organic acids. Acidogenesis further reduces the mixture into hydrogen and carbon dioxide by converting simple molecules into fatty acids and hydrogen sulfide. This process requires heat energy, so the temperature of the waste decreases.

Step 3: Anaerobic Acetogenesis

The volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen during this stage. The temperature of the waste further drops to between 60 degrees Fahrenheit and 104 degrees Fahrenheit.

Step 4: Anaerobic Methanogenesis

The fourth stage is the most productive and longest. The microbes use up hydrogen to create methane and carbon dioxide. While this process in a landfill can take decades when in a contained tank, it can produce power for homes and vehicles.

Step 5: Aerobic Decomposition

In a landfill, the process returns to the first stage once the acetate is converted to methane. However, in a controlled environment, the solids are removed and converted to fertilizer, while the first stage starts over with fresh manure.

What Oak Ridge Dairy Gets Out of an Anaerobic Digester

In addition to fertilizer for our crops, we can pipe the methane and carbon dioxide mixture to a processor using existing piping. The processor separates carbon dioxide from methane. Before separation, methane has only half of the heating capacity of natural gas. However, once the two gasses are separated, methane has nearly the same heating capacity as natural gas and can be used to power a home or even run a biodiesel vehicle.

Just about five cows from our herd can produce enough methane to power one home or two diesel-equivalent vehicles for a year.

Our herd at Oakridge Dairy has the following offsets:

• 9,947,314 miles driven by a gasoline-powered vehicle.

• 450,934 gallons of gasoline are consumed.

• 9,278 barrels of oil.

• 1,387 tons of waste are recycled instead of going to landfill.

• 780 homes’ electricity use for a year.

Contact the Modern Milkman

Create an account with the Modern Milkman to support a green farm and get fresh milk and dairy products. We deliver milk from Oakridge Dairy plus fresh-baked goods from local farms.

We deliver weekly and have three different subscriptions:

• The Full Share: Your choice of any six products.

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We provide milk in glass half-gallon containers from Oakridge Diary, plastic gallon containers from Guida’s Dairy, butter, bread, rolls, eggs, yogurt, chocolate milk, sour cream dips, cookies, and more.

You can change your subscription weekly or add extras through our a la carte menu. Our milk goes from the cow to your front door – we guarantee that it is fresh as we milk the cows, pasteurize and homogenize the milk, then bottle it and send it on its way – all in 24 hours or less.

When you want fresh milk and want to support a green operation, visit the Modern Milkman and sign up for a subscription today.