Anaerobic Digestion and Biogas

Find out more about anaerobic digestion for heat, biogas, electricity, and fertiliser

Since Marks and Spencer announced plans to become carbon neutral by 2012 (1) anaerobic digestion has received its fifteen minutes of fame. UK high street giant Marks and Spencer plan to trial anaerobic digestion as a way of reducing the amount of waste they send to landfill and to heat some of their stores, offices, and distribution centres.

An anaerobic digester can be used to process any kind of organic matter from sewage to waste food products. Naturally occuring bacteria rapidly break down the matter (in the Marks and Spencer case food waste) into three main products: biogas (2) - primarily methane (50-70%) and CO2, acidegenic digestate - similar to compost, and methanogenic digestate - a nutrient rich liquid.

The biogas can be used to produce renewable electricity or burned directly for commercial and domestic heating. The waste products can be used as fertilisers and soil improvers which are superior to chemical equivalents and environmentally friendly.

Although carbon dioxide is released during anaerobic digestion, the carbon was only recently absorbed by plants and so is part of a complete carbon cycle. This released gas does not contribute to global warming in the same way that carbon released from fossil fuels does - that CO2 has been trapped underground for millions of years.

Methane gas from landfill sites is collected and burned.

If the organic waste processed in an anaerobic digestor was instead dumped in a landfill site, the methane and carbon dioxide would be released into the atmosphere, so we should exploit the energy it contains. In addition, huge quantities of energy can be saved which would have been used to transport large volumes of waste to landfill. Currently most landfill sites simply collect and flare (i.e. burn) the methane gas generated underground wasting a valuable resource.

Web Link References

(1) http://www.reuk.co.uk/Marks-and-Spencer-Carbon-Neutral-by-2012.htm
(2) http://www.reuk.co.uk/What-is-Biogas.htm

Article from REUK.co.uk:
http://www.reuk.co.uk/Anaerobic-Digestion-and-Biogas.htm
Published: 31st January 2007
© REUK 2009