The plants act as pressure-cookers conditioning sludge, the leftover solids from wastewater treatment, at high temperatures. The sludge is then transferred to existing anaerobic digesters to be broken down. This produces biomethane gas that is then burned to create heat and generate renewable electricity.
Thames Water said sewage sludge that has gone through this process before being anaerobically digested creates significantly more biogas with which to generate electricity to run its treatment works.
Last year the water company reduced its power bills by around £15 million by generating 14 per cent of its annual energy requirements from sewage. The six new plants should increase this to 20 per cent.
Lawrence Gosden, director of capital delivery, said: “As well as being environmentally friendly, generating energy from waste also reduces our running costs by protecting us from the price fluctuations of the mainstream, non-renewable energy markets, bringing savings that help to keep customers’ bills down.”
The plants will be installed at Beckton and Riverside sewage works in Essex, Crossness in Thamesmead, Longreach in Barking, Oxford and Crawley sewage works by 2015.