Turning food into fuel
When we throw food away we are essentially throwing away energy. But we don't have to eat a left-over takeaway to make use of the energy stored inside it. Food waste can also be used to generate electricity.
Anaerobic digestion (AD) is a treatment process in which unpackaged food waste, garden waste or sewage is composted in the absence of oxygen. This produces a biogas which can then be burnt to generate electricity and heat.
Since we currently bin a third of our food, dumping 6.7 million tonnes every year, we certainly have plenty of fuel.
AD is already widely used elsewhere in the world. Denmark has a large number of farm co-operative AD plants that produce electricity and heating for local villages. India and Thailand have several thousand small-scale plants, whilst home and farm-based AD systems provide cheap, clean energy in many other developing countries.
However, in the UK most of our biodegradable waste is sent to landfill where it breaks down and releases methane – one of the most harmful greenhouse gases.
The remaining organic waste is mostly composted. But because AD generates energy, offsetting emissions from fossil fuel power stations, it gives higher net carbon savings than composting.
In November 2007, M&S signed an agreement with AD firm Greenfinch for energy generated from household food waste. The Shropshire based plant will provide us with 1.3 Gigawatt hours of energy – enough to meet the needs of two of our stores.
We have already signed a second agreement with an AD plant in Somerset, and plan to generate an increasingly large proportion of our energy from this 100% renewable source.
Anaerobic digestion could potentially provide the UK with about 2% of our total energy needs.
So today’s leftovers could generate the power to heat tomorrow’s dinner.
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