The U.K.’s sewer system, built in the 19th century to halt cholera epidemics, may play a role in tackling climate change as it unfolds as the environmental crisis of the next 100 years.
Some of the pipes in Britain’s 624,000-kilometer (388,000 miles) sanitation network can get as warm as 21 degrees Celsius (70 degrees Fahrenheit). That’s because water flowing into the system from toilets and plug holes has collected heat from the air around and from household appliances.
Capturing that warmth as a source of renewable energy could provide enough heat for more than a third of London each year, according to figures released Thursday by trade association Scottish Renewables and the utility Scottish Water Ltd.
The technology could help government ministers increase the share of renewables used to supply heat, which is among the biggest sources of pollution. They’re seeking to meet a target to cut greenhouse gas emissions by 57 percent in 2030 from 1990 levels.
Taking carbon dioxide out of heat may be the biggest challenge facing U.K. energy policy over the coming decades, according to the regulator Ofgem. While electric utilities are investing in wind and solar power, it’s harder to cut emissions associated with heating, which accounts for a third of carbon pollution in the U.K.
“Heat is so crucial,” said Stephanie Clark, policy manager at Scottish Renewables, said by phone. “It’s so important, and our sewers contain enough natural heat to do so much. The technology is there. It’s just a case of using it.”
More than 11 billion liters (2.9 billion gallons) of water is collected in sewers from bathrooms, kitchens and rainwater run off from roads every day in the U.K., according to the Department for Environment, Food and Rural Affairs. A single liter of that could provide almost 6 watt-hours of heat, according to Scottish Water Horizons.
Capturing heat from sewers is already being tested in cities around the world, from Cologne, Germany to Philadelphia, Pennsylvania. The U.K. in 2015 installed its first system for recovering heat from waste water.