Originally posted in another forum in April 2020, and then on this site as a page.
You might find this post interesting if you are thinking about recycling your food waste, or not bothering to recycle it. In the UK "recycling" usually means sending the waste to an anaerobic digester (an AD). Anaerobic digestion is the process of taking biomass (often food waste, but not always) making a soup out of it, then feeding the soup to bacteria which generate biogas, a mixture of methane and CO2. Usually the gas is burned to create electricity. The headline numbers:
- there are 486 ADs in the UK, of which 119 have a generating capacity of 1 MW or more. The total generating capacity is 429 MW. As a comparison, EDF's West Burton gas-powered station has three 430 MW turbines.
- the biggest site is a 14.4 MW digester in Cambridgeshire fed with maize.
- the biggest fed with food waste is a 6 MW Biffa site in Staffordshire taking 120,000 tonnes of waste pa. Other plants take manure and slurry, brewery wastes, wonky veg, pomace. This is "sustainable" energy but it's only as sustainable as the feedstock. Overall UK ADs consume 12.5m tonnes of feedstock.
I went to see an AD at Cattlegate Farm in Enfield and another operated by Severn Trent Green Energy at St Albans. The St Albans plant is about twice as big as Cattlegate. Both are fed by domestic and supermarket food waste. The waste is tipped into a pit and fed to a machine which separates the organic matter from the plastic packaging, which is extruded at the back of the machine. At the time of my visit to St Albans the feedstock looked to be mainly unsold chicken korma. There are a lot of truck rolls to keep this plant working: trucks bringing waste in (I saw one from Harlow, which is quite a way away), trucks taking the plastic away (it goes to an incinerator), trucks taking the digestate away to be sprayed onto farmland. The gas is fed to two big engines which together produce 2.8 MW: that's approx 22,000 MWh a year, assuming availability of 90%. The AD occupies a lot of real estate for a relatively small amount of power. It takes in 48,500 tonnes of food waste, ie 2.2 tonnes of waste to generate one MWh of electricity (think of a cube of yuck about 1.3m on a side). The wholesale price of electricity in UK varies a lot, between about £35/MWh and £65/MWh. A cube of yuck would be worth about £50 once it's been turned into electricity.
The St Albans AD gets about a third of its revenue from charging the people who dump the waste and the rest from selling the power that it produces. For the environment the real benefit of ADs is that they divert waste from landfill and so prevent methane from escaping to the atmosphere.
Note added 31 March 2026: Councils in England are due to start weekly food waste collections today under the Simpler Recycling regulations. WRAP warns that food waste collections could normalise waste rather than preventing it. In a survey 63% of respondents already using collections said that it had made them to try harder to reduce what they throw away; but 44% felt more relaxed about wasting food, knowing it could be recycled rather than sent to landfill. WRAP estimates that UK households waste 4.4 million tonnes of edible food annually, costing £17 billion in total or roughly £1,000 for a household of four.
Deploy Methane Digesters | Project Drawdown
Crops grown for bioenergy 2008-2020 (GOV.UK) Section 3: anaerobic digestion.
Post. Category GB clean power tags anaerobic digestion.
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