GreenfinchBiogen's digester in Shropshire

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Defra and AD The EA and AD Renewable Energy Association AFOR

Anaerobic digestion (AD) is gradually gaining popularity in the recycling sector as a way of treating municipal food waste. The process has traditionally been used on a small scale on farms to treat wet materials like slurry but some companies have built larger facilities capable of treating food waste from municipal sources and more are in the planning stages.

The first facility built to treat municipal waste was the GreenfinchBiogen plant – originally operated by Greenfinch - in Ludlow, Shropshire. The 5,000 tonne-a-year capacity facility opened in 2006 and takes source separated food waste from households in South Shropshire. A number of other organics recyclers have also received planning permission to build more municipal food waste digesters.

The process is different to composting because it happens anaerobically, or, without oxygen. It produces a digestate, which is more watery than compost and can be used as a soil improver. Methane gas is a by-product of this process and is converted into electricity which can either be used locally or sold on to the National Grid.

The government has shown lots of support for AD and is working to increase take-up of the technology. In February 2009, waste and recycling minister, Jane Kennedy outlined 'shared goals' for AD to ensure the technology is established by 2020. Steve Lee, chief executive of the Chartered Institution of Wastes Management (CIWM) is also leading a task force to ensure AD becomes an established technology.

ROCs

Financial incentives are also available to make the technology more attractive. At present the government is the technology double ROCs. ROCs are Renewable Obligations Certificates, which are green certificates issued by providers of renewable energy to energy suppliers. As part of the Renewables Obligation Order, which came into effect in 2002, electricity suppliers must source an increasing proportion of electricity from renewable sources.

To prove they have met these targets, suppliers must present ROCs and, if targets are not met, they have to pay money into a fund which is, in turn, paid back to suppliers who have successfully met their renewable obligations. As ROCs from AD are set to be worth double there is a lot of incentive for suppliers to use energy produced by AD.

Quality Protocol and PAS 110

The Quality Protocol for Anaerobic Digestate was published in January 2009 and is awaiting approval by the Technical Standards Committee at the European Commission. The organic recycling sector expects approval from the Committee by summer 2009. If the Protocol is approved it will reclassify digestate as a product and not a waste. A BSI PAS 110 safety standard is also in development and is at the final draft stage. The standard will assure the quality of digestate produced from AD.