WRAP is often asked by local authorities to provide a description of anaerobic digestion that is written in plain English. The paragraphs below provide some information on the process, why it is a good thing and what happens to the material going through it.
Anaerobic digestion (AD) involves breaking down biodegradable material using micro-organisms in the absence of oxygen. It is already used to treat wastewater at sewage treatment works in the UK but can also be used to treat other organics wastes, including household food waste, farmyard manures and energy crops.
The process of anaerobic digestion provides a source of renewable energy, since the food waste is broken down to produce biogas (a mixture of methane and carbon dioxide). When food waste is sent to landfill, it breaks down in the same way but the biogas goes straight into the atmosphere where it contributes to climate change. Methane is 25 times more damaging than carbon dioxide.
The biogas can be used in a standard gas engine or combined heat and power (CHP) unit to generate renewable electricity and heat. The electricity can then be either used locally or exported to the National Grid. Alternatively, the biogas can be cleaned up to produce biomethane and injected into the gas pipelines for use in household heating and cooking. Once cleaned it can also be used as a vehicle fuel in the right types of engine instead of regular fuels like petrol and diesel.
AD also produces a rich bio-fertiliser, which is high in valuable nutrients such as nitrogen, phosphorus and other elements required for healthy plant growth and fertile soil. This can then be used back on farmland to grow more food and keep the soil healthy.
To find out more or to see some projects that are using AD, go to our more detailed information on anaerobic digestion.