What’s it all about?
Anaerobic Digestion (AD) is a process that uses naturally occurring bacteria which can grow in the absence of oxygen to breakdown organic wastes such as waste food and other biodegradable wastes.
The process generates biogas (a mix of methane and carbon dioxide) which can be used to generate heat and power for industry and homes, or to provide a transport fuel. It can also produce a nutrient rich solid and liquid fertiliser called digestate, which can be used as a soil conditioner to fertilise land.
Almost any organic material can be processed with AD, including waste paper and cardboard (which is of too low a grade to recycle, e.g. because of food contamination), grass clippings, leftover food, category 3 animal by product waste, industrial effluents, sewage and animal waste.
The Good Stuff
- Diverting food waste away from landfill to anaerobic digestion prevents the release of biogas into the atmosphere, as this biogas is often captured and combusted to produce heat, electricity or both. This biogas includes methane, a greenhouse gas which is up to 21 times more damaging to the environment than carbon dioxide.
- The biogas is a source of renewable energy which contributes towards the UK’s renewable energy requirements.
- Other uses for the biogas include feed in to the mains gas grid and using it as a vehicle fuel, after it has been cleaned up.
- The technology is scalable from small farms up to large centralised treatment facilities making it very flexible.
- A further by product of the AD process is a nutrient rich biofertiliser.
- Not only does AD reduce the need for landfill, it reduces the environmental impact of waste disposal, produces energy and provides marketable commodities as by products
Not so Good
- Capacity - There are currently around 37 Anaerobic Digestion facilities in the UK using food and farm waste with a further 60 planned or under construction. Transport distances in the short term may be prohibitive but will improve as capacity increases.
- AD does not treat all wastes, only the organic fraction
- Most AD plants are looking for de-packaged food waste and do not currently operate any front end segregation or de-packaging processes, material collected or delivered to these facilities would require source segregation including most packaging.
- AD can be expensive
- Be clear about what waste can go into AD as there can be specific rules that impact the success of this as a disposal route.
- If you have animal by products (ABP) you need to be aware of government guidelines on how this should be managed to avoid cross contamination – see Netregs/DEFRA
- Some AD plants can take category 3 ABP but you need to check their process is authorised to handle ABP waste
- Handling waste for AD can be a messy and unpleasant job so ensuring you have the right environment to do this and equipment to help.
- Leakages are a potential risk, so checks need to be made on any skips or containers you use. If you are storing outside you need to ensure that you are not contaminating any land or leaking into drains.
- Duty of care needs to be carried out as with all waste with special care taken to ensure that the correct ABP licences are in place.
- For further information on AD visit the WRAP website
Frequently Asked Questions
Q: What does the UK produce that can be used in anaerobic digestion?
A: The UK produces over 100 million tonnes of organic material that is suitable for treatment by AD. This includes:
- 12-20 million tonnes of food waste (from households and industry)
- 90 million tonnes of agriculture by-products like manure and slurry
- 1.73 million tonnes of sewage sludge.
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