Anaerobic digestion(AD)is the sequential breakdown of organic matter to produce biogas and digestate.Many see it as the cornerstone of a circular economy,processing biodegradable substrates-from energy crops to commercial food waste and sewage sludges-to deliver renewable energy and residues to fertilise crops.UK water and sewerage companies(WaSCs)produce around a third of a billion cu m of biogas each year.But together the agricultural,waste and industrial AD sectors produce almost double this-almost three-quarters of a billion cu m of biogas from 670 sites.Biogas is 60-65 per cent methane,plus carbon dioxide;each cubic metre contains around 6 kilowatt hours of energy.The UK aerobic digestion sector produces almost five terawatt hours of energy a year,to heat more than 800,000 homes.
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