What happens to your food waste

Anaerobic digestion plant at Cassington

All raw and cooked food waste is collected weekly and recycled, instead of landfilled.

Food waste collected from homes in West Oxfordshire is taken to an 'anaerobic digestion plant' at Cassington where it is converted into fertiliser for farmland and electricity. Anaerobic digestion involves breaking down biodegradable material using micro-organisms in the absence of oxygen.
The food waste is fed into a large underground tank via a machine that cuts the waste up into pieces less than 10mm. Liquid waste from commercial companies such as breweries and dairies is fed into a separate underground tank but goes through a similar process.
The food and liquid waste are mixed together by computer which automatically decides the quantities of each to make the best mixture. This is then pasteurised in tanks at 70 degrees for 2 hours to kill any germs and prevent possible spreading of e-coli, foot and mouth etc. The tanks are heated by reusing the excess heat from the engines which are used to make the electricity.
The waste is then pumped into large vats which maintain a temperature of approximately 40 degrees. Stirrers inside the vats keep the waste moving to make sure no cool zones develop. Each of the five vats has the capacity to hold 4,500 tonnes of waste.
Food waste is kept in the first vat for around 50 days. It is then pumped through a macerator to cut the waste up further and then into another vat for a further 25 days to achieve better break down of the waste.
As the food waste breaks down it produces biogas (a mixture of methane and carbon dioxide) and a liquid fertiliser. The methane is extracted from the biogas collected in the vats and fed into gas engines to generate renewable electricity and heat. The plant uses around 12% of the electricity it produces itself, the remainder is fed into the national grid.
The remaining liquid is used as fertiliser on local farms as it is high in valuable nutrients such as nitrogen, phosphorus and other elements required for healthy plant growth and fertile soil.