Fuel of the future
10 Sep 2010 by Evoluted New Media
An unpleasant combination of out-of-date food, animal manure and sewage sludge could be the key to a greener Britain if the Government can thrash out an action plan to increase anaerobic digestion plants across the country.
An unpleasant combination of out-of-date food, animal manure and sewage sludge could be the key to a greener Britain if the Government can thrash out an action plan to increase anaerobic digestion plants across the country.
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Food waste could be converted into biogas and provide up to 7% of the UK’s renewable energy requirement |
It is estimated that digesting one tonne of food waste via anaerobic digestion can save between 0.5 and 1 tonnes of CO2 equivalent over sending it to landfill and the Government is considering how to use this technology after visiting a cutting-edge plant from BiogenGreenfinch in Northamptonshire.
“Today I’ve seen first-hand how food scraps and out-of-date supermarket food is a valuable resource that can generate energy – rather than rubbish to be thrown away,” said environment minister Lord Henley. “As we strive to be the greenest government ever, this is exactly the type of technology we should be looking at, particularly as it cuts greenhouse gas emissions.”
In an anaerobic digester, food waste fed into a large, sealed and insulated vessel with controlled heating and mixing – no air is allowed in and no methane escapes. It is broken down by bacteria at 35-40°C in four distinct stages. First is hydrolysis, where large molecules of carbohydrates, fats and protein are broken down into smaller water-soluble units. These are converted to volatile fatty acids by bacteria in the second stage – acidogenesis. In the third stage – acetogenesis – this is converted into acetic acid. Finally the acetic acid is used by methane-forming bacteria to produce the gas.
The methane gas is captured and generates renewable electricity and heat, or can be upgraded to biomethane that can be injected into the National Gas Grid. The digestate undergoes pasteurisation to kill pathogens and is used as a high-nutrient biofertiliser on farmland twice a year.
Lord Henley said that there had already been constructive discussions with industry and farmers and that teams at Defra and the Department for Energy and Climate Change (DECC) are now working towards an action plan to examine how to take practical steps towards using anaerobic digestion. The UK currently produced around 100 million tonnes of biomass waste per year – enough to generate 7% of the renewable energy required by the UK by 2020.
