Is the hidden heat in our sewers a huge untapped energy source?

In another green energy world-first for Scotland, Borders College today became the first public building anywhere on the planet to be heated by sewage. Policy Manager Stephanie Clark writes on the hidden heat beneath our feet.

While Scotland prepares to shiver through another winter, the water flowing through the sewers beneath our feet could prove to be one of our last great untapped renewable energy assets.

Bubbling along at up to 21c, the sewage in Scottish Water’s drains contain hidden heat which could be tapped to warm our homes and businesses.

This week saw the official opening of a project which will do just that - in another green energy world first for Scotland.

Borders College in Galashiels has binned its gas boilers and is now warmed by the waste water and sewage flowing under its classrooms and workshops.
The project, installed by Leicester-based SHARC Energy Systems, shreds the solid waste in the flow, separates it, then runs the liquid part through two huge heat pumps to produce water at 60c, which then circulates round the site’s existing radiators.

The water is then discharged back into the sewer having given up 5c of its latent heat.
When Energy Minister Fergus Ewing unveiled a plaque to launch the scheme on Tuesday, the water flowing into the system was just 11c. Heavy rain meant runoff from fields and roads had been diverted into the sewer over previous days, diluting the waste water from toilets, showers and dishwashers, which remains almost a constant 21c throughout the year.

This hidden heat, in combination with tried-and-tested heart pump technology, has the potential to make a significant impact on Scotland’s target of sourcing 11% of its heat from renewable sources by 2020.

It's heartening to see the Scottish Water and the UK Green Investment Bank stepping in to back this pioneering approach to heat: there is clearly a growing interest in tapping this exciting – if slightly smelly – energy source.