Thames burns its sludge

Burning sewage sludge or the methane derived from it helped Thames Water cut its electricity bill by £15M in 2008/09. The process enabled the company to generate 14% of its power needs.

Dr Keith Colquhoun, the company’s climate change strategy manager, said the development is “good news because we treat 2.8Bl of sewage every day at our 349 works. The solids have a high calorific content that we use to generate electricity”.

Thames Water aims to cut greenhouse emissions by 20% of its 1990 levels by 2020 – about 200,000 tonnes less CO2. By using the sludge along with other renewable energy sources, Colquhoun said the company is making significant progress towards this target after cutting emissions by 5% in the past two years, despite grid energy becoming more carbon-intensive.

Thames Water has the largest renewable electricity generation capacity inside the M25, excluding the commercial electricity generators, and it uses two methods to generate power from sewage:

  • Thermal destruction with energy recovery, in which sewage sludge is burned to generate power
  • Anaerobic digestion, or CHP (combined heat and power) generation, when methane derived from sewage sludge is burned to created heat and in turn generates power.

Several of Thames Water’s sewage works have CHP plants, including Maple Lodge (Rickmansworth), Mogden (Isleworth), Oxford, Reading, Beddington (Surrey), Swindon, Bishops Stortford, Banbury, Aylesbury, Basingstoke, Bracknell, Camberley and Crawley.

The company also has two facilities in East London that use thermal destruction: Beckton, north of the River Thames, which is Europe’s largest sewage works treating about 3.5 million people’s waste daily; and Crossness, south of the river, which treats the human equivalent of 2 million people’s waste.

Once the sludge has been used to generate electricity, Thames Water offers it to farmers for use as fertiliser or to developers as a landscaping material or soil improver.

In 2008/09 Thames Water put all of its sewage sludge to beneficial use, sending none to landfill and saving millions of pounds in landfill tax.

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