Anaerobic Digestion

Anaerobic Digestion (AD) is what happens when biomass (such as food or crops) rots down in the absence of air producing a combustible gas (a mixture of methane and carbon dioxide) and a residue with a high nutritional value as a fertiliser. It occurs naturally, for instance in swamps, and has been harnessed for many years in the UK through the capture and utilisation of the gas produced at sewage works or in landfill sites.

AD is an efficient way of harnessing nature to capture the energy and nutrients contained in the putrescible (i.e. easily rotted) fraction of our waste. With the increasing political hostility to landfills, attention has turned to more controlled approaches, where the process is managed and stimulated in highly-engineered systems to release the gas at a higher quality (i.e. a higher methane proportion) in a short space of time and to recover the nutrients by producing a fertiliser from that part of the waste stream that is not converted into a gas. Although AD has broader connotations, it is commonly used as a term to refer to the recovery of energy and fertiliser from putrescible wastes.

Summerleaze established its subsidiary, Andigestion Ltd, in 2004 to develop and commercialise AD technology. Andigestion is now the largest producer of electricity by AD of domestic, commercial and agricultural wastes in the country, accounting for around 70% of the electricity produced in this small but developing sector.

To learn more about AD and Andigestion, click here to visit Andigestion's own site.