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A super-charged technology

You cannot have missed all the fuss about using anaerobic digestion (AD) to treat food waste. Some are happy to promote in-vessel composting or home composting as a way of dealing with food waste. But what about trying autothermal thermophilic aerobic digestion?

Vertal, based in Mitcham, south London, is already running a facility using this process, and by the looks of the busy yard and facility, it is already doing well even though it opened as recently as January this year. So what is autothermal thermophilic aerobic digestion (ATAD)?

“It’s a bit of a mouthful,” admits Vertal founder and managing director Leon Mekitarian. “ATAD is essentially super-charged composting. We are an in-vessel system digesting food waste very rapidly using air (see box).” I ask Mekitarian why he sees the technology as an alternative to AD.

“The waste industry is not a very complex one,” he says. “It is all about value for money and fast return on capital investment. Our plants are cheap to build, fast to operate, and occupy a small footprint [in terms of land required]. So we represent a very cost-effective alternative to AD technology, which tends to be large-scale, requires large amounts of land, large amount of capital and an uncertain regulatory future in terms of renewable obligation certificates.

“It is a local solution. Our plants are compact and can be sited in urban locations close to sources of waste. We are an urban, industrial society here in the UK, and most of the food waste is produced in towns and cities. Locating plants near to that source of waste is an obvious thing to do. Our process is fast, so therefore it is cost effective to run and operate,” he adds. “We can be competitive in the marketplace. Our fertiliser is high in nutrients. Somebody wants it: it is a saleable material.”

But one difference with AD is that it is not possible to get electrical energy from the process.

“Our outputs are carbon dioxide [although it has a small carbon footprint] and water vapour. But our other output is what is most important and sets us aside from an alternative system and that is our fertiliser output,” he says. “Our output is a fertiliser, not a compost nor a digestate. It is a nutrient-rich organic material high in N, P and K [nitrogen, phosphorus and potassium] and organic matter.

“An ATAD system captures nutrients and stabilises them in the process very quickly. Our fertiliser output is high in nutrients and is capable of displacing petrochemical fertilisers used in agriculture readily today. So we have a ready market for our outputs. At the moment, it is destined for commercial agriculture in Surrey.”

This merchant plant is capable of treating up to 70,000 tonnes of food waste each year, and was set up with the help of £5m investment from alternative asset manager Foresight Group. Current customers include local authority food waste collected from households, as well as supermarkets, hotels, restaurants, schools and food factories. All of these are based in London.

Vertal has expansion plans and hopes to bring this technology to other parts of the UK.

“Our plans are to establish a network of facilities across the UK,” says Mekitarian. “[These will be] located in strategic places close to volumes of source-separated food waste. There is a chronic shortage of capacity within the UK, and has been since the Animal By-Products Regulations were introduced in 2003. Our [technology] is an obvious solution to the interim and longer term position for food waste.”

Vertal is working hard to show that it is possible to have an alternative to AD to treat food waste. If the plant in Mitcham is anything to go by, this ATAD technology could definitely have a place in the UK’s infrastructure as an alternative to AD and composting processes.


As a rather useful schematic on the Vertal website shows (, food waste is delivered into the facility in either its packaging or in bags, which are removed in the process. It is put into a hopper and then moves into a pre-shredder. From there, the material is conveyed via an overbelt magnet to remove ferrous materials and then an overbelt eddy current separator to remove the non-ferrous.

From there, the food waste is delivered to a fine crusher macerator and then transferred into digester vessels for treatment. Giant aeration fans move air into the vessels which, using bacteria, heat the waste naturally up to 80˚C, which allows it to be used to treat category 3 animal by-products.

From the digester vessels, the material is sent to product storage tanks, with waste heat being used to warm the office complex. Finally it goes to a dewatering unit, to leave a dry fertiliser output that can be delivered to customers such as farmers for putting on their land. The whole process takes about 72 hours and the food waste is completely pasteurised in this timeframe.


Born and educated in Ireland, Mekitarian attended agricultural college in Cirencester. Struggling to find work in the economic downturn of the early 1990s, he moved sideways and helped to set up a recycling division for a recycling company in the south west of England and helped it to thrive during the next 10 years. In 2003, he left it to work on this technology and set up Vertal.

The best thing to happen in my career was…
“It was to complete the funding and construction of the Mitcham facility in less than nine months. We started fundraising a month before the credit crunch began in September 2008, and we managed to close the financing in February 2009.

“It isn’t that hard to get up to £1m from most venture capitalists, but not that easy to get it for technology start-ups. When you have got one plant up and running it is much easier. We were lucky that we had the right solution, the right team and food waste was the right sector.”

The worst thing to happen in my career was…
“Fundraising for the facility. Trying to raise money after the credit crunch was a nerve-wracking experience, but we were fortunate to get the finance.”


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