Anaerobic Digestion

Livestock slurry releases methane and nitrous oxide into the air.
Anaerobic digestion captures these gases and turns them into clean, renewable energy.

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The Climate Issue

Slurry isn’t just waste. It’s a major source of emissions. Left in open tanks or lagoons, it breaks down anaerobically and releases methane, a gas over 80 times more potent than CO₂ in the short term.

Even with careful spreading, slurry contributes nitrous oxide and ammonia, harming air quality and raising the farm’s footprint. Yet this organic material contains valuable energy, if captured before it escapes.

Today, most of that energy is lost into the atmosphere.

The Solution: Anaerobic Digestion

Anaerobic digestion (AD) is a controlled process that breaks down slurry and other organic matter in sealed tanks. Instead of releasing methane to the air, it collects it and uses it as biogas, an on-farm energy source that can power generators, boilers, or be upgraded to biomethane.

The leftover material, called digestate, is rich in nutrients and can be spread as fertiliser with lower emissions and odour. On dairy farms, AD helps close the nutrient loop, cut greenhouse gases, and create new income from renewable energy.

Unlock Farm-Level Impact

Key Benefits applying Anaerobic Digestion

Cut Methane

Capturing methane from slurry before storage prevents one of the largest sources of GHG on livestock farms.

Renewable Energy

Biogas can power the farm, reduce reliance on fossil fuels, and generate income when sold to the grid.

Fertiliser Use

Digestate is more plant-available than raw slurry, easier to handle, and releases fewer emissions when spread.

Impact of Applying Anaerobic Digestion

Anaerobic digestion (AD) reduces methane emissions during storage, produces biogas that can offset fossil fuel use, and creates digestate that retains fertiliser value. AD also supports nutrient circularity and helps reduce synthetic fertiliser dependence.

Research from Teagasc and EU models shows that AD systems processing 5,000–10,000 tonnes of slurry per year can:

Cut methane emissions by 65–90%
Lower GHG intensity by 0.05–0.09 kg CO₂-eq/kg milk
Generate 200–400 MWh of energy annually
Deliver net benefits only where capital costs, energy prices, and policy supports align

While AD can deliver strong environmental gains, system viability depends on installation costs, energy revenue, and support schemes. Farmers must assess feasibility on a case-by-case basis.

Scenario	Slurry sent to AD	Energy Output (MWh/year)	GHG Emissions	% GHG Reduction
0% sent to AD	-	-	0.960 kg CO₂-eq/kg milk	0% kg CO₂-eq/kg milk
50% sent to AD	50%	200	0.911 kg CO₂-eq/kg milk	5.1% kg CO₂-eq/kg milk
100% sent to AD	100%	400	0.870 kg CO₂-eq/kg milk	9.4% kg CO₂-eq/kg milk

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Considerations

Capital Investment

AD systems are expensive to install, especially for smaller farms. Grants, cooperatives, or shared digesters may be needed to reduce risk.

Feedstock Volume

Successful operation requires steady input of slurry and/or other biomass. Farms must ensure consistent supply and storage logistics.

Operational Expertise

AD plants require skilled management. Gas handling, digestate storage, and system maintenance are essential for safety and efficiency.

Implementation

Anaerobic digestion is a long-term investment. But for suitable farms, it offers a high-impact way to reduce emissions and build energy independence. Here’s how to approach it.

1. Assess suitability. Farms with high livestock numbers and sufficient slurry volume are best suited. Consider site access, zoning, and integration with current systems.

2. Explore funding. Look for CAP, EU Innovation, or national renewable energy grants. Group investment with neighbours can help reach a viable scale.

3. Plan for digestate use. Ensure spreading and nutrient plans make full use of the digestate, replacing synthetic fertiliser and closing nutrient loops.

Behind the Research

ODOS Tech was founded by Cian White and Alejandro Vergara, two sustainability specialists with deep expertise in agricultural climate action.

Alejandro (left), a PhD in environmental engineering from University College Dublin, helps farmers measure their carbon footprint and implement mitigation strategies to reduce their impact. Cian (right), a researcher at Trinity College Dublin with a PhD in ecology, works on restoring nature to increase biodiversity on farms using satellite imagery to monitor habitats.

Together, they helped lead the carbon and nature-based work for the Farm Zero C project at Shinagh Farm, one of Europe’s first net-zero dairy pilots. At ODOS, they build smart, science-based tools to help agri-food businesses protect the environment and restore nature.

Research

Teagasc MACC

Teagasc analysis shows that AD is one of the most effective tools for reducing methane on livestock farms, especially when combined with nutrient recycling.

Farm Zero C Pilot

At Shinagh Farm, potential for a small-scale digester was assessed to reduce emissions from slurry, improve nitrogen efficiency, and generate heat for buildings.

EU Renewable Energy Strategy

The EU views AD as a key pillar of the Renewable Energy Directive. It supports biomethane development and offers policy incentives for on-farm installations and grid injection.