Scope for recovering heat from Scotland’s sewers

Scotland’s sewers contain enough natural and discarded heat to warm a city the size of Glasgow for more than four months a year, according to figures produced by Scottish Water Horizons for Scottish Renewables.

Put another way, nearly a trillion litres of wastewater and sewage are flushed down Scots toilets and plugholes every day – using heat pumps and wastewater recovery systems could be used to harness some of that energy potential, preventing the emission of more than 10,000 tonnes of carbon dioxide each year.

Water in UK sewers can be as warm as 21°C, and it maintains a constant temperature throughout the year, says Scottish Renewables.

Scotland’s wastewater and sewage are transmitted through more than 31,000 miles of sewers to over 1,800 wastewater treatment facilities. Donald MacBrayne, Business Development Manager with Scottish Water Horizons, 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.’

‘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,’ he added. 

Scottish Renewables Policy Manager Stephanie Clark said: ‘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.’

Scottish Renewables points to the UK’s first wastewater heat recovery system, which was installed at Borders College in Galashiels in 2015. It captures warmth from sewage and uses it to heat classrooms on campus. The system uses a heat pump to amplify the natural warmth of waste water. The heat captured is being sold to Borders College under a 20-year purchase agreement.

Grant support for further wastewater heat recovery projects in Kirkwall, Campbeltown, Clydebank, Stirling and Glasgow were recently announced.