Can you use poo to generate power?

By Rhys L Griffiths and Peri Jones

Everybody poops. In fact the human race produces over 1,000,000 tonnes of the stuff every day. With fossils fuels running out and concerns growing over the levels of carbon dioxide in our atmosphere, could we turn all this waste into something useful? Could we use poo to generate power?

Researchers at Stanford University have developed a way to generate electricity from sewage bacteria. This involves their use of microbes that can create electric energy as they eat organic material. Before we get in too deep, let’s have a look at how a normal fuel cell works and how we get electricity in batteries.

By R.Dervisoglu – Own work, based on http://en.wikipedia.org/wiki/File:Solid_oxide_fuel_cell.svg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=19314043

Chemical fuel cells work by taking advantage of the chemical reactions that happen in some materials, similar to batteries. As you can see in the image, fuel enters the left side and into the anode (negatively charged electrode) chamber. The fuel typically used is hydrogen as the anode then reduces the fuel to ions and electrons. The reaction results in an excess of electrons which are then carried along the circuit towards the cathode (positively charged electrode). The flow of electrons mean that the system has an electric current running, resulting in electrical energy.

Unlike a typical battery, which have a limited supply of stored energy, fuel cells can have continuous electrical energy as long as it has fuel and oxygen. When the electrons reach the cathode, it is oxidised and there is a release of usually water (H2O) or carbon dioxide (CO2). So for the system to continue, oxygen is needed in the right-hand side chamber to re-oxidise the cathode for the oxidation reaction to repeat.

So back to poo…

CC University of Stanford – Poo Battery

The researchers placed groups of these microbes around the negative node of a battery. Then as the microbes consumed organic matter (poop), the excess electrons are sent across to the cathode which is made of silver oxide. Over the course of a day, the silver oxide is oxidised by the electrons and results in a silver node. For this process to continue, the battery needs to be re-oxidised by oxygen as done in the conventional fuel cell. Currently the poop battery is capable of extracting roughly 30 percent of potential energy stored in sewage.

Another way of creating power using poop involves digging rather deep wells. A water reclamation plant in San Pedro injects sludge into wells over a mile deep. The pressure and heat causes the waste to release enough methane to power 3,000 homes. This gas can be responsible for keeping your radiators warm, giving you a warm shower and even heating up your food on your gas hob.

Creating methane gas can be very useful when it comes to renewable energy. A few months ago I spoke to an environmental scientist from GENeco called Laura Blake and she told me about a project that GENeco has worked on called the Bio-Bus


The Bio-bus is the first bus in the UK to be powered by gas derived from food, sewage and commercial liquid wastes. GENeco takes the waste and allows it to decompose without oxygen for roughly three weeks at 32 – 42 degrees Celsius. This produces biomethane gas which (after being scrubbed for impurities) can be used to power the Bio-Bus. The bus can travel over 300 km on a full tank of gas, an amount of fuel which can be produced by the annual food and sewage waste of just five passengers. The widespread use of gas-powered vehicles has the potential to improve urban air quality. To read more about the Bio bus then click here.

CC GENeco – The Bio Bus

The video above features in our KS2 Science and Engineering show Who want’s to be a Superhero? where we talk about careers in science.  The section with Laura looks at renewable energy and the importance it has to our planet. We also look at how civil engineers design strong bridges, how electronic engineers can send data through lasers and how aeronautical engineers keep planes in the sky.  If you’d like us to visit your school or festival with this show then please get in touch.

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Posted in Biology, Chemistry, Engineering, Physics, Technology