Renewable energy technologies could be used in sewer systems to heat cities across Scotland, according to new research.

New figures produced by Scottish Water Horizons for Scottish Renewables reveal how the country's sewers contain enough natural and discarded heat to warm a city the size of Glasgow for more than four months a year.

With 921 million litres of wastewater and sewage flushed down Scottish toilets and plugholes every day, Scottish Renewables said capturing warmth contained in the waste could help prevent over 10,000 tonnes of CO2 emissions entering the atmosphere each year.

Stephanie Clark, Policy Manager at the industry body, 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.

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"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."

Water in UK sewers can be as warm as 21c, and maintains a constant temperature throughout the year. With millions of Scot's wastewater/sewage transmitting through over 31,000 miles of sewers to more than 1,800 wastewater treatment facilities, Scottish Water Horizons' Business Development Manager Donald MacBrayne, said the water "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," he said.

"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 waste water treated every day, the opportunities presented by heat recovery are significant. We are now using heat maps to actively explore locations where such heat recovery schemes could be developed and are working with a number of public bodies and commercial businesses to progress the opportunity."

In it's draft Energy Strategy, the Scottish Government is aiming to achieve 50% of all energy coming from renewable sources by 2030.

Ms Clark added: "More than half of the energy consumed in Scotland is in the form of heat.

"As a society, we take warm homes and workplaces and constant hot water for granted, but it's vital we reduce the amount of carbon emitted by the sector if we're to tackle climate change and meet existing and proposed targets."

(LM/MH)