Biogas from Dairy Manure

A biogas system, often called an anaerobic digester, captures gas given off as manure breaks down and uses it for power, heat or fuel. It can work well on the right farm and be a poor fit on the wrong one.

Key points

Biogas systems capture methane from manure and turn it into energy.
They fit confinement herds with steady manure collection best.
Costs, labor and permits are significant, so verify every figure.
Biogas and manure structures are confined space hazards.
Visit operating farms and compare written quotes.

How a digester works

Manure is collected and fed into a sealed tank or covered lagoon. Microbes break it down without oxygen and produce biogas, which is mostly methane. The gas is cleaned and then burned in an engine to make electricity and heat, or processed for other uses.

What is left, called digestate, still holds nutrients and is usually applied to crops under a nutrient management plan.

The size of the system should match the manure supply. Too little manure leaves an engine underused, and too much without enough storage or handling causes trouble. Ask the vendor to show the manure assumptions in writing.

Is your farm a good fit?

Digesters work best where manure can be collected regularly and in quantity, such as in confinement barns with scraped or flushed alleys. Grazing herds that spread manure on pasture collect much less. Herd size, manure consistency and bedding type all affect results.

Ask whether the project makes sense on your own manure supply or whether it depends on bringing in outside material, which brings its own rules.

Bedding matters more than many farmers expect. Some bedding materials break down well in a digester and some do not, and sand can settle and cause problems. Ask the vendor how your current bedding would be handled before you commit.

Reliable manure collection
Herd size and stability
Bedding type and solids
Distance to utility connections
Staff time for daily monitoring

Costs, income and programs

Digesters take large investment and ongoing labor. Income can come from power sales, heat use, reduced bedding costs or payments tied to environmental programs, but terms change and are not guaranteed. Ask for written projections that show how they were calculated.

Check with USDA, your state energy office, your lender and your utility for current programs. Have an accountant and a lawyer review any contract. This is general information, not financial advice.

Ask about the full cost over many years, including repairs, engine rebuilds, labor and insurance. A cost estimate that only covers construction leaves out much of what you will actually spend.

Safety around biogas

Biogas is flammable, and it can release gases that are dangerous or deadly in enclosed spaces. Digesters, pits and tanks are confined spaces. Never enter without proper training, air monitoring, rescue plans and equipment.

Follow manufacturer, OSHA and extension guidance. Keep ignition sources away from gas lines and equipment. Train every worker on emergency procedures and post warning signs.

Hot work, welding and grinding near gas equipment need a permit process and a trained crew. Ask the vendor for a written lockout and emergency plan, and walk every employee through it before the system starts up.

Never enter tanks or pits alone
Use trained crews for maintenance
Keep flames and sparks away from gas
Test and ventilate before any work
Keep emergency contacts posted

Managing the system day to day

A digester is a living system that needs steady feeding, temperature control and monitoring. Plan for daily checks, regular maintenance of engines and pumps and a plan for downtime.

Ask the vendor about service response times, spare parts and training. Talk to farms that have operated a system for several years, not only new ones.

Keep a log of gas, power output, feed rates and temperatures. Small drifts in these numbers are often the first sign of a problem, and a good record helps the service technician fix it faster.

Common mistakes and what to ask

Common mistakes include overestimating gas output, underestimating labor and ignoring the cost of connecting to the grid. Another is overlooking air, water and odor permits.

Ask for references and visit working sites. Compare quotes and ask for performance guarantees in writing.

Talk with your neighbors before building. Odor, truck traffic and noise can matter to the people living nearby. Good communication early prevents misunderstandings later. Check local zoning and air permit rules as well.

Finally, keep a plan B. If the engine is down for a long stretch, you still have to handle manure and keep cows milked. Ask what the farm will do with gas and manure during repairs.

What manure supply does this design assume?
What permits are required?
What is the staffing requirement?
Who services the engine and how fast?
What if gas output falls short?

When to get help: Contact your state environmental agency about permits, your utility about connection, and your lender before committing. Ask your extension specialist to review projections.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

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