More than 900 million litres of waste water and sewage is flushed down toilets and plugholes in Scotland every day. Water in sewers can be as warm as 21C (69.8F).
Already employed in Canada, the heat-recovery technology involves the use of a heat exchanger to extract energy from waste water and transfer it as heat to the clean water network.
This provides heating, cooling and hot water for export to nearby homes and buildings.
As the technology uses a closed-loop system, waste water never comes into contact with the clean water flow.
With versatile application, the technology can be installed within a wide range of buildings, either as a retro-fit or as part of a new-build, and is particularly suited for locations with a large number of people within a relatively small area.
Dr Tadhg O’Donovan, Associate Professor in the School of Engineering and Physical Sciences at Heriot-Watt University, said: “Heat is a very valuable energy resource, accounting for 79% of UK Domestic Energy used, and its value is often underappreciated.
“18% of UK Domestic Energy used is for water heating and significant proportion of this heat is ‘flushed’ away in waste water.
“While the temperature of this waste water is lower than we generally want, the use of heat pumps are a very efficient and low carbon way of ‘upgrading’ the heat to make it useful, so I could see this being a worthwhile exercise and a useful contribution to energy saving and carbon reduction.”
Scottish Water has a vast infrastructure including 32,000 miles of sewers which carry waste water from homes and businesses to around 1,800 treatment works across Scotland.
Donald MacBrayne, from Scottish Water Horizons, said he believed heat in waste water was 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 waste water treated every day, the opportunities presented by heat recovery are significant.
“Not only does this help contribute to a sustainable circular economy, it also helps to alleviate fuel poverty, meet Scottish Government’s target of 11% of heating from renewable sources by 2020, and tackle the threat posed by climate change.”