A new state-of-the-art anaerobic digester will turn London food waste into enough gas to power thousands of homes. Mike Farish reports.
People who have a conscience about letting uneaten food go to waste will soon be able to sleep a little easier – at least if they live in the London area. That is because the city will soon be served by a state-of-the-art recycling facility just now in the process of being commissioned that will have the capacity to turn 160,000 tonnes per year of waste that would otherwise go to landfill into 14 million cubic metres of biomethane gas that can be fed into the supply grid. According to the company behind the facility, that’s enough to power 12,600 homes for a year.

The facility in question is the new ReFood plant in Dagenham out towards the eastern margin of the city, a smart looking installation of gleaming white buildings and brightly reflective metal piping which represents a total investment in both the land and the actual processing plant of some £32m. It will form the focal point for a citywide collection system of food waste and for larger scale recycling of liquid waste from food-related manufacturing. In the first case the sources of the waste food will generally comprise both restaurants and non-commercial institutions such as hospitals. In the second, likely sources might include, for example, breweries or any drinks manufacturing operation.
The mix is actually important because the process involves diluting the solid food waste with enough liquid to enable it to be pumped through the pipes and tanks of the facility and to act as a catalyst for the process itself. According to Philip Simpson, commercial director for ReFood, the process at Dagenham that converts the material into both usable gas and also fertiliser for use in agriculture is essentially that of anaerobic digestion (AD) – a well-established set of procedures and technologies.
The food waste arrives at the plant entirely conventionally in green plastic ‘wheelie bins’ of the sort found in any domestic residence. The bins are unloaded from the delivery vehicles in the central reception building in which the atmosphere is both ionised and slightly pressurised and are then taken to a station where they are automatically inverted to empty their contents into chutes that take their contents into the system. “Food waste is unloaded, de-packed and blended to create a homogeneous mix,” said Simpson. After a mechanical process to separate out any non-food material, the mixed, de-packed food waste is then heated to a temperature of 70degC to pasteurise it in order to neutralise any harmful bacteria, before being passed through a heat exchanger – which reverses the heat cycle to cool the product – and into a holding tank.
The next step in the now fully automated process sees the waste stream passed from the holding tank to one of the four digesters on the site with feeding taking place every 30 minutes.
The digestion process involves the food waste being broken down by different strains of bacteria.

In the first stage bacterial hydrolysis of the blended food waste breaks down the cell structure of organic molecules such as carbohydrates making them available for the other bacteria. Then acidogenic bacteria convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia and organic acids. Those organic acids are then further converted into acetic acid plus further ammonia, carbon dioxide and hydrogen by acetogenic bacteria. At the final stage, methanogenic microbes convert these products to methane and carbon dioxide in the process known as methanogenesis. The complete flow-through time for the process is some 30 days.
The combined methane and carbon dioxide is then scrubbed to remove any acid gases, followed by water washing to remove the carbon dioxide. The final stage sees the calorific value of the refined biomethane tested to ensure it meets the requirements of the National Grid before being compressed and exported down the pipe. The gas consumed in the pasteurisation stage represents only about five per cent of that produced by the process as a whole, so the net contribution to the grid is still considerable.
Moreover, the remaining material can be used as an organic bio-fertiliser. Indeed, the material marketed by ReFood under the name ReGrow is already produced at two already established processing facilities in Widnes and Doncaster.
Simpson said that the new Dagenham plant includes a number of upgrades in both the processing and bio-fertiliser production stages. The company is also seeking a BREEAM (Building Research Establishment Environmental Assessment Method) ‘Excellent’ rating, which would place it in the top 10 per cent of all UK new non-domestic buildings assessed that way.
Despite the benefits the process can bring in turning what would otherwise be waste into usable energy, the overall UK situation is somewhat mixed, according to Simpson. “In Scotland, Wales and Northern Ireland, significant steps have been taken to prevent food waste from being sent to landfill,” he said. “However, in England we have no such barriers to using landfill for the disposal of food waste.”

Even despite the lack of a landfill ban in England, the UK now has over 500 anaerobic digestion plants in operation. In contrast to the new Dagenham plant, though, the vast majority use crops such as maize, which are specifically grown for the production of energy. In fact, says Simpson, “it is believed that around 30 per cent of UK maize yield is now being used as a feedstock for AD plants.”
But using prime agricultural land to produce energy crops while allowing the landfilling of a far more suitable feedstock such as food waste is plainly not efficient at any level. As such, claimed Simpson, the argument for more facilities like the Dagenham plant are becoming more convincing: “The current volume of food waste being landfilled would support over 80 plants similar to Dagenham and produce enough biomethane for more than one million homes,” he said.
If the PR is to be believed, these facilities more or less pay for themselves. So, wouldn’t it be a sensible government initiative to provide one of these facilities at every major city ?
Yes
You would think so would you not.. until one runs into the good Liberals of Guildford for example – who are so keen on saving the planet that they make sure that plans for such a plant are always rejected. It has of course, nothing to do with property values.
Yes and no. This technology is still developing at a rapid pace. These plants need a government subsidy such as the Feed In Tariff (FIT) or Renewable Heat Incentive (RHI) to give a modest return on investment within the lifetime of the project. Until the technology develops to a point where it requires less CAPEX and becomes more efficient, these projects will always require a helping hand from the government. Unfortunately we have seen a big reduction in this support despite the massive benefits of both crop/farm waste plants and food fed plants and their contribution to the circular economy, reducing landfill and as a domestic source of energy.
Great to have a digester but London is not as bad as the article implies. It’s not all landfill, a great deal of food waste goes into LondonWaste’s compost facility and hence into gardens and agriculture.
Your first caveat probably answers your second question. Though rather than HMG, what about Tesco, Morrisons, Asda, etc joining together to do so. Wait a minute: that would mean that they were doing something valuable together: and that is not what competition needs! We leave collusion to ‘fix’ prices, etc to the banks and the rest of the shams. I believe it was Dr Johnson who opined that “whenever members of one group meet, it is usually to agree something NOT of benefit to the general population?”
It was Adam Smith in his Wealth of Nations:
“People of the same trade seldom meet together, even for merriment and diversion, but the conversation ends in a conspiracy against the public, or in some contrivance to raise prices.”
Thank you Michael, I knew it was someone important! As I get older I know that many of my faculties are not as sharp as they used to be. I must confess that my memory is not as good as it was, and frankly, I cannot remember the rest!
What happens to the CO2 scrubbed out?
It is collected and can be then used for other things. In the case of some plants the CO2 can be compressed and used by drinks manufacturers and other industry.
Don’t forget that land fill sites need organic waste if they are to generate gas to drive the electricity generators.
Like Mr Perry, I am interested in what happens to the CO2. Is it extracted from the water after washing, to go to a CCS facility? Or is it just allowed to release to atmosphere?
The Engineer published another article on the 22nd June reporting on a new catalyst that converts CO2 from the air into Syngas – a collaboration opportunity perhaps??
Would say that the order ought to be:
1. Reduce food wastage – wasteful 2 for 1 offers encourage waste as do expensive small loaves etc, it is cheaper to buy a large loaf than a small one in supermarkets.
2. Compost and recycle this organic content.
3. Burn or digest the waste according to economic calculations. AD just converts to gas fired heating: incineration generates heat and power with economy of scale.
If I recall, during one of our several recent mini-wars there was meja reports that , HMQs Forces were fed with ‘out-of-date’ food from the large super-markets: offered free, and still totally fresh and edible. I do love the story that just before Christmas one year, the opposition learned which refrigerated trucks (coming overland from Pakistan) had the turkey dinners thereon and blew such up. A fresh consignment had to be sent by air!
Even better, a plant in Swindon is being built to convert non-recyclable black bin waste in bio synthetic natural gas – even better.
The value of gas production is that it is easily stored.