Thames Water says it will spend £250 million ($37.7 million) on thermal hydrolysis process (THP) plants to enhance its “vast poo power” program, which converts sewage sludge to electricity.
The UK water company saved about £15 million ($22.6 million) last year on its power bills by generating 14 percent of its annual energy requirement from sewage.
THP plants — essentially industrial-scale pressure cookers — condition the leftover solids from wastewater treatment by heating it up to around 160 degrees Celsius.
The pre-conditioned sludge then goes into existing anaerobic digesters (pictured) that break it down, producing biomethane gas that is then burned to create heat and generate renewable electricity.
Sewage sludge that has gone through the THP process before being anaerobically digested yields significantly more biogas with which to generate electricity to help run Thames Water’s treatment works. By using anaerobic digestion alone, about 45 percent of the organic material in sludge turns into biogas. Thermal hydrolysis increases this to between 60 and 65 percent, says Lawrence Gosden, Thames Water’s director of capital delivery.
By installing THP at six of its main UK sewage works, along with other renewable energy activities including solar power, Thames hopes to meet its goal of generating 20 percent of its electricity demand from renewable sources by 2015.
Thames Water will install the new THP plants at four London locations — Beckton and Riverside sewage works in Essex, Crossness in Thamesmead and Longreach in Barking — along with Oxford and Crawley sewage works by 2015.
Four of these plants will benefit from a sewage version of a cider press, which will squeeze out 40 percent more water from the sludge before it goes through the thermal hydrolysis and anaerobic digestion processes.
Using THP also means there is less solid matter left over at the end, which will halve the number of trucks needed to take it from the sewage works to farmland where it is used as fertilizer recycling the organic material back into the soil. This will save the company around £2 million ($3 million) every year.
Generating its own power from sewage and also solar panels has helped Thames Water reduce its carbon emissions by 16 percent on 1990 levels.