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15 June 2017, 05:37
Scotland's sewers contain enough heat to warm a city the size of Glasgow for more than four months a year, according to figures by a renewable energy group.
A total of 921 million litres of wastewater and sewage - enough to fill 360 Olympic swimming pools - are flushed down toilets and plugholes in Scotland every day.
Capturing warmth contained in discarded water could prevent more than 10,000 tonnes of harmful CO2 entering the atmosphere every year, new analysis has claimed.
Statistics produced by Scottish Water Horizons for Scottish Renewables show how technologies such as heat pumps and wastewater recovery systems could harness that energy potential.
Renewable energy experts said water in UK sewers can be as warm as 21C (69.8F) and maintains a constant temperature throughout the year which "could heat a city the size of Glasgow'' over a four-month period.
Stephanie Clark, policy manager at Scottish Renewables, said: "These new figures show the enormous scale of the energy we are literally flushing away every day.
"Water which is used in homes and businesses collects heat from the air around it, as in a toilet cistern, or is heated, as in dishwashers and showers. That's in addition to the energy that it gains from the sun when stored in reservoirs.
"Technology now exists which allows us to capture that energy and waste heat can play an important role in helping us reach our challenging climate-change targets.''
Scotland's millions of litres of wastewater and sewage are sent through more than 31,000 miles of sewers to over 1,800 wastewater treatment facilities.
Donald MacBrayne, business development manager with renewable technology business Scottish Water Horizons, believes heat in the wastewater is a valuable commodity.
He said: "Water that is flushed down the drain from homes and businesses represents a significant source of thermal energy.
"Usually, this heat is lost during the treatment process and when treated effluent is returned to the environment.
"By tapping into this resource using heat recovery technology we can provide a sustainable heating solution which brings both cost, carbon and wider environmental benefits.
"With almost 32,000 miles of sewers pipes across Scotland and more than 900 million litres of wastewater treated every day, the opportunities presented by heat recovery are significant.''
Gina Hanrahan, acting head of policy at WWF Scotland said: "While it may be a surprise that clean heat can be generated from seemingly dirty sources, we shouldn't turn our noses up at the amazing waste heat our sewers offer.
"These kinds of innovative solutions have an important role to play in cutting emissions and creating jobs.''