a toilet seat and paper

Heat From Waste

In the search for new and sustainable energy sources, few people realise that there is an energy source flowing beneath the surface of our cities. Sewage!

This abundant, free energy source remains mostly untapped. However, there are several companies looking to make this a new normal way to reduce the amount of valuable heat lost to the environment.

Borders College on the Scottish Borders is the first project in the UK to use waste water that we get rid of down sinks, showers and toilets, and recycles it to make use of the heat that would otherwise be lost. The college gets 95% of its heating from the sewer that runs nearby on its way to a waste water treatment factory.

The makers of the Borders College system state that around 30% of all energy in the world ends up in the sewer.


When we flush our toilets, or drain our showers and baths, there is heat stored in the water that is carried away.Now, it’s not a very hot heat, but by using a heat pump, the temperature of this water can be raised to a level that can be used to heat (or cool) buildings and water. This is known as a heat recovery system.

Scottish Water waste heat infographic
Image credit: Scottish Water
(Click to open full-size image)

The infographic above shows the process from waste water coming from homes and businesses to the sewer to returning to our homes and businesses as hot (and clean!) water.

Systems like the SHARC system used at Border’s College, separate the liquid and solid waste that are on their way to waste treatment plants, before transferring the liquid waste, which has been thoroughly cleaned, to a heat pump where the temperature is raised enough that we can use it in our homes and businesses.

The benefits of this system is that by removing the amount of waste heat going into the environment, we are improving air quality and making our heating more sustainable.

Recycling water this way also saves money because we are not needing to use as much natural gas that we would normally use to heat (or cool) our homes, water and food.


Waste water isn’t the only unusual way people are looking to save energy in their heating. There is a swimming pool in Worcestershire near Birmingham that uses the waste heat from a nearby crematorium to heat the pool!

Heat could also be taken from the vents on the London Underground and used to power the Tube stations.

How do you feel about using waste heat this way? Answer our poll below and see if you’re of the same opinion as others!

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