Here’s a curious, if earthy, one to ponder next time nature calls: Thames Water, London’s water and sewerage company – and producer of renewable power.
Most people know about the first bit. Fewer, however, are aware that we also generate electricity, and lots of it, from our 13 million customers’ flushings, using a process we call “poo power”.
We are, if you will, the poo power market leader, the largest non-commercial producer of electricity inside the M25, responsible for 40% of all the renewable energy across all the water and sewerage firms in England and Wales.
This electricity helps run our sewage works, reducing dependence on more costly, often less eco-friendly power from the national grid, and dovetailing neatly with our goal of cutting our carbon emissions by 20% on 1990 levels by 2015.
In 2008/09 we generated through poo power enough electricity to run about 40,000 average-sized family homes – 14% of our entire energy requirement – saving £15 million in power bills. That’s cash that would otherwise have come out of customers’ bills. Right now we’re up above 15%.
And with grid energy not forecast to get any cheaper, poo power makes increasing economic, as well as environmental, sense. Water and sewage is heavy stuff to pump around, so the more power we produce the better.
That’s why over the next five years we’re planning to invest up to £250m expanding our poo power capabilities by around 50%. The aim is to capture as much biogas (methane) as possible from the 2.8bn litres a day of sewage we treat so we can maximise the power potential of our seemingly limitless renewable resource.
We use two methods to generate power from sewage. The first is anaerobic digestion, or CHP (combined heat and power) generation, where methane derived from sewage sludge – the dried-out solids in sewage – is burned to created heat, which in turn generates electricity. The second, used only at Beckton and Crossness sewage works in East London, is thermal destruction with energy recovery, where sewage sludge, dried into blocks called “poo cake”, is burned to generate heat and power.
From 2010 to 2015 new CHP plants are set to be built at Beckton and Crossness, in addition to the sewage sludge incinerators at both sites, while new CHP equipment, to maximise biogas yield and so boost electricity output, is also planned for Riverside (East London) Aylesbury, Beddington (South London), Chertsey, Oxford and Crawley sewage works.
All this will take us from the 204 Gigawatt hours (GWh) of electricity we generated in 2009/10 to a predicted tally in 2015/16 of 318 GWh – more than 20% of the company’s annual power requirement, enough to power nearly 70,000 homes – after all the planned investment is complete.
So there it is, a relevant topic to mull on a forthcoming visit to the WC.
Additional information on Thames Water’s poo power endeavours
· Poo power is nothing new. We’ve used anaerobic digestion for 70 years. But we’re always looking for new ways to hone our processes.
· The following Thames Water sewage works have CHP plants: Maple Lodge (Rickmansworth), Mogden (Isleworth), Rye Meads (Herts), Deephams (Edmonton), Oxford, Reading, Long Reach (Dartford), Slough, Hogsmill (Kingston), Beddington (Surrey), Swindon, Bishops Stortford, Banbury, Aylesbury, Basingstoke, Bracknell, Camberley, Crawley, East Hyde (Luton) and Wargrave (Berks).
The author is press office manager at Thames Water