Thames Water to tap more sewage power
13 Mar 2013
London – Thames Water is extending its use of THP (thermal hydrolysis process) technology in an effort to build on the energy-cost savings already achieved with this process.
THP effectively pressure-cook waste sludge - the leftover solids from wastewater treatment - by heating it up to around 160°C. The pre-conditioned sludge then filters into existing anaerobic digesters, which break it down, producing biomethane gas that is then burned to create heat and generate renewable electricity.
Last year, Thames Water said it saved around £15 million off its power bills by generating 14% of its annual energy requirements via the use of THP. By installing THP at six of its main sewage works it aims to increase this figure to 20%.
“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,” stated Lawrence Gosden, director of capital delivery at Thames Water.
More gas is produced through thermal hydrolysis because it breaks down the walls of the organisms within the sludge, in particular the cell walls, so the nutrients are more easily released.
“By using anaerobic digestion alone, about 45% of the organic material in sludge turns into biogas. Thermal hydrolysis increases this to between 60 and 65%,” added Gosden.
Using THP also means there is less solid matter left over at the end, which will reduce by half the number of lorries needed to take it from the sewage works to farmland where it is used as fertiliser; recycling the organic material back into the soil, saving Thames Water £2 million per year.
By using sewage biogas to generate electricity, greenhouse gas emissions are cut and in turn uses a waste product to help run its activities and maintain power at several of its sewage works.
