These days’ ideas for renewable energy seem to be coming from everywhere: the sun, the wind, and now, science is slowly working on cost effective ways to human waste into energy. We’re not there yet, but things are looking good for this unconventional energy source.

 Biosolid is the politically correct term for poo, particularly when it comes to using it for energy.  Biosolids can be turned into methane, oil and electricity. Methane is a natural gas that powers your heater and stove, meaning that these everyday household items could be powered by your poo! There are two ways to turn these golden nuggets into methane: biological and thermochemical.

Biological conversion involves using living things, like algae or bacteria, to breakdown the poo into chemicals that can then be turned to methane. Some bacteria that can convert poo into hydrogen gas (H₂) and carbon dioxide gas (CO₂) which can then be turned into methane (CH₄). And some algae are so clever that they can convert our poo directly into carbon dioxide and methane. The problem with using biological conversion is that while algae are making methane, they also create carbon dioxide, which is a major contributor to global warming. So this defeats the whole purpose of the exercise of re-using poo to save the environment. To fix this, scientists are currently looking for other types algae that can breakdown carbon dioxide before it hits our atmosphere.

 Thermochemical conversion is basically burning the poo to create energy. High temperatures are used to breakdown the elements in our biosolids, like carbon and hydrogen, and turn them into fuels that can be used for energy.  This process is pretty efficient at extracting all the available energy from our poo, and it has a small carbon footprint. In London and Paris thermal processes are already in place to convert biosolids into energy. Londoner poo (including the Queen’s!) makes more than 11 megawatts of electricity a year!

So why isn’t all our poo being burnt into energy?

The problem is, when the waste is burned, almost 25% of it turns into ash. In London alone 17,000 tonnes of ash need to be disposed of each year. 

 Another problem is that Biosolids, no matter which process is used, contain heavy metals like zinc, copper and mercury. These need to be removed before we can get energy.

 With the world focused on saving our energy it’s exciting to think that instead of being users, we could all be contributors. In the future, when our children and grandchildren look up at us with wide eyes and ask “What did you do to prevent global warming?” we can proudly say, “Don’t worry, I did my bit.”

Milne,C. (1974) The Enchanted Places. Methuen