Every year, vast quantities of wet organic waste—from farm slurries to food processing residues—are disposed of in ways that release methane straight into the atmosphere and risk polluting land and water. Anaerobic digestion (AD) offers a proven alternative: a controlled, oxygen-free process that breaks down this waste, captures the methane it produces, and turns it into usable energy, while leaving behind valuable fertiliser and compost by-products.
What Is Anaerobic Digestion?
Anaerobic digestion is the biological breakdown of organic material by bacteria in an oxygen-free (anaerobic) environment. It’s widely used as a waste treatment process, but its real value lies in the by-product it generates: a methane-rich biogas that can be burned to produce heat and/or electricity.
At its simplest, an AD system consists of three core components:
- A heated digester tank, where the breakdown of waste takes place
- A gas holder, which stores the biogas produced
- A gas-burning engine/generator set, if the biogas is being used to generate electricity
Depending on the nature of the waste and the operating temperature, up to 60% of the organic waste fed into the system can be converted into biogas. This biogas typically has a calorific value of 50–70% that of natural gas, and it can be burned directly in modified natural gas boilers or used to power internal combustion engines.
Up to 60% of input organic waste can be converted into biogas with a calorific value of 50–70% that of natural gas.
The system described in this datasheet has been engineered specifically to be high-rate, while also being capable of managing refractory (hard-to-break-down) solids—a combination that isn’t always easy to achieve in AD design.
How the Process Works
The digestion process happens inside a warmed, sealed, airless container—the digester—which creates the ideal environment for bacteria to ferment organic material. The tank must be kept warm and thoroughly mixed to maintain the conditions bacteria need to convert waste into biogas, a mixture predominantly made up of carbon dioxide and methane, along with small amounts of other gases.
The process unfolds in three distinct biological steps:
1. Hydrolysis (Decomposition)
Plant or animal matter is broken down into smaller, usable molecules such as sugars. This is the initial decomposition stage that prepares the waste for further breakdown.
2. Acid Formation
The decomposed matter is converted into organic acids by acid-forming bacteria.
3. Methane Formation
Finally, these organic acids are converted into methane gas—the valuable energy-rich component of biogas.
Temperature Control
Process temperature has a direct effect on the rate of digestion. Most systems operate in the mesophilic range (30°C–35°C / 86°F–95°F), which offers stable, reliable performance. It’s also possible to run digesters in the thermophilic range (approximately 55°C / 131°F), which can speed up digestion, but this comes with a caveat—thermophilic operation is more prone to upset if not closely and continuously monitored.
| Parameter | Typical Value |
|---|---|
| Waste converted to biogas | Up to 60% |
| Biogas calorific value (vs natural gas) | 50–70% |
| Mesophilic operating temperature | 30°C–35°C (86°F–95°F) |
| Thermophilic operating temperature | ~55°C (131°F) |
| Odour reduction | Up to 80% |
Key Advantages
Anaerobic digestion isn’t just a waste disposal method—it delivers a wide range of environmental and commercial benefits:
- Well-proven technology that can be installed and operated with confidence
- Biogas production without significant air pollution issues
- Odour and nuisance control, with reductions of up to 80%
- Waste minimisation, maximising the final repository volume available
- Social and environmental benefits through avoided greenhouse gas release and renewable energy production
- Relatively low-tech operation, not requiring highly sophisticated control systems to run successfully
- Commercial by-products, including fertiliser, compost, ammonia and electricity
Why It Matters: The Broader Attributes of AD
Reducing Greenhouse Gases
Methane is a potent greenhouse gas when it escapes into the atmosphere. Conventional disposal of slurry and food residues allows this to happen naturally. AD captures that methane instead, using it as fuel—so a well-managed scheme maximises methane generation while preventing any release to atmosphere, reducing overall emissions.
Energy Production Without Net Carbon Increase
Because AD relies on organic feedstock rather than fossil fuels, it provides an energy source with no net increase in atmospheric carbon dioxide. Displacing fossil-fuel-derived energy with biogas helps reduce the risks associated with climate change.
Displacing Finite Fossil Fuels
AD feedstock is renewable and doesn’t deplete finite fossil fuel reserves. The energy generated can directly reduce demand for fossil fuels, and the resulting fibre and liquor by-products can reduce reliance on synthetic fertiliser—which itself requires fossil fuels to manufacture.
Recycling Nutrients
The liquid fertiliser and fibre produced by AD, when applied correctly, can reduce the need for synthetic fertilisers as part of a wider fertiliser management programme.
Reducing Land and Water Pollution
Poorly managed disposal of animal slurries is a well-known cause of land and groundwater pollution. AD introduces an integrated management system that significantly reduces this risk—along with the risk of regulatory fines.
Reducing Odour
AD can cut odour from farm slurries and food residues by as much as 80%, a meaningful benefit for sites near residential or sensitive areas.
AD systems can reduce odour from farm slurries and food waste by up to 80%, while simultaneously producing renewable energy and fertiliser by-products.
Typical Applications
Anaerobic digestion systems like this are well suited to a range of wet organic waste streams, including agricultural slurries, food processing residues, and other biodegradable organic materials. They’re particularly valuable for organisations looking to combine waste treatment obligations with renewable energy generation and by-product recovery.
Flexible ownership models are also available, including options for vendor-financed ownership and operation, making it easier for organisations to adopt AD technology without significant upfront capital investment.
Key Takeaways
- Anaerobic digestion breaks down organic waste in an oxygen-free environment, converting up to 60% of it into biogas.
- Biogas has 50–70% the calorific value of natural gas and can fuel boilers or generator sets.
- The process runs through three stages—hydrolysis, acid formation, and methane formation—typically within the mesophilic temperature range.
- Beyond energy, AD delivers fertiliser, compost and ammonia by-products, reduces odour by up to 80%, and helps cut greenhouse gas emissions and pollution risks.
- Vendor-financed ownership and operation models can make adoption more accessible.
Get in Touch
If you’re managing wet organic waste streams and want to explore how high-rate anaerobic digestion could reduce your disposal costs, cut emissions, and generate renewable energy and valuable by-products, we’d love to hear from you. Contact our team today to discuss how an AD solution could be tailored to your site’s needs.