Can we use human excrement for fuel?

09 October 2011

Question

Hi Dr. Smith,

I've always wondered if human waste can, or is being used, to produce electricity.  I know that rotting cow manure and garbage can produce energy, but I've never heard of human waste used for this purpose. Seems like a great source of energy, and the infrastructure to collect it is certainly in place.  Can you shed some light on this?

Matt Fisher
Washington State

Answer

We put this to Dr. Piers Clark, Commercial Director at Thames Water...

Piers - In Thames Water, we've made energy from poo for many, many decades now and we do it through a process called anaerobic digestion. Anaerobic digestion is a process that's very similar to what happens inside your stomach actually when you eat food. It also happens when we ferment berries to make beer. It's basically the gradual breakdown of organic matter through a natural process and the molecules that make up the food that we eat and that ultimately come out as poo gradually get broken down into a form of a gas and the gas is called biogas. It's a mixture of methane and carbon dioxide. And carbon dioxide is naturally in the air and methane is the gas that people most readily associate with being the gas that you burn on your cookers at home. We run this natural process and have done so for many years. We produce about 15 million pounds worth of energy every year which equates to about 15% of our total energy usage in Thames Water.

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