Supermarkets burn food waste as anaerobic digestion shortage bites

Asda and Sainsbury’s are to stop landfilling their food waste by sending it to combined heat and power plants. The Environment Department has set up a task force aimed at rapidly increasing the uptake of anaerobic digestion.

Asda and Sainsbury’s are disposing of food waste in combined heat and power (CHP) plants, highlighting the current lack of anaerobic digestion capacity.

In February, Sainsbury’s began sending all food waste from its 28 Scottish stores - some 56,000 tonnes per year - to renderer Prosper de Mulder (PdM). Meat is separated for rendering and packaging for recycling before the waste is burnt at PdM’s biomass CHP plant in Widnes, Cheshire.

Sainsbury’s will extend the scheme to all stores by the summer. Some material will go to PdM’s biomass CHP plant at Hartshill, near Nuneaton.

Asda has also started sending waste from 20 of its stores to PdM. Waste is back hauled to Asda’s distribution centre in Skelmersdale, Lancashire, where it is separated into animal by-products for rendering and other materials suitable for CHP. Some material also goes to Veolia’s waste CHP plant in Sheffield, said Julian Walker-Palin, Asda’s head of sustainability. The company aims to roll out the scheme nationwide by summer 2010.

Both supermarkets have long said they want to use anaerobic digestion (AD) to treat food waste. It is considered more efficient than incineration. Waste is digested in the absence of air to produce a methane-rich biogas that can be burned and a digestate.

Sainsbury’s already sends about 60 tonnes of food waste per week from 40 stores in the Midlands to Biogen Greenfinch’s AD plant near Bedford. However, both supermarkets say increasing their use of AD is not possible due to a dearth of facilities. There are only a handful of plants taking commercial or municipal waste across the UK and just 10-20 on-farm systems (ENDS Report 404, p 30-33 ).

"Ideally all biodegradable waste would go to AD," said Mr Walker-Palin. "We’d be creating a virtuous circle with our waste becoming material that can be used on farmland. But we’ve found that the infrastructure just doesn’t exist." Existing AD plants do not have equipment to depackage all wastes, he added.

"PdM is very aware our aim is AD, but we have to accept there isn’t enough capacity out there run by skilled operators," said Alison Austin, Sainsbury’s environment manager. "There are a lot of people entering the market, but we know from trials that AD is difficult to get right - there’s a lot of technical science to it - so we will only move to AD if we’re happy with those doing it."

DEFRA aims to address the capacity shortfall. In February, it launched a "vision document" for AD that says the government intends to make the UK a "world leader" in the technology.1 This is a surprising claim given Germany has 3,000 on-farm systems alone. The vision has the backing of Asda, Sainsbury’s and bodies including the National Farmers Union, Water UK and National Grid. A cross-government and industry task group will be set up to develop an implementation plan.

PdM itself is developing a network of AD plants across its existing rendering facilities. Last year, it submitted a planning application for a 45,000 tonne per year plant at its Doncaster site. The company was expecting to receive planning permission for the plant as ENDS went to press.

Philip Simpson, PdM’s commercial director, said the company will transfer some of Asda’s and Sainsbury’s waste to the AD plant once it is operational at the end of 2009. However, the treatment of waste has to be based on logistics, he said. "It’s pointless trucking material hundreds of miles to an AD plant, just to say you are. It’s got to be based on proximity and the value you can get from the material. At the end of the day, our biomass plants deliver more power. They have been designed specifically to burn wet biomass."

Mr Simpson added that AD should only be used where there is a market for the digestate produced. "There’s only a limited market for the digestate. With our CHP plants we produce ash, but that can go into aggregates." The Doncaster plant will send its digestate to farms in Lincolnshire.

  • The UK’s major supermarkets are committed to reducing the amount of food thrown away by households by 155,000 tonnes between 2008 and 2010. The target was announced in January and develops the Courtauld Commitment of 2005 (ENDS Report 367, p 29 ). It is equivalent to just 2.3% of the 6.7 million tonnes of food households throw away annually.

    Signatories to the Commitment say they will improve labelling so customers do not throw food away before its use-by date and make pack sizes more suited to their customers’ needs. Bread manufacturer Warburtons has already introduced a smaller pack size - 600 grams compared with its usual 800g - in response to some customers saying they did not need such large packs.

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