Engineering energy from waste

Posted by Professor Ioannis Ieropoulos on 15 May 2018

Can we get robots to be energetically autonomous?

The Bristol BioEnergy Centre within the Bristol Robotics Laboratory has been investigating energy autonomy for engineering systems and robots for nearly 17 years. It all started with the question Can we get robots to be energetically autonomous? and this has been pursued through the investigation and development of the microbial fuel cells technology.

MFCs are in fact bioelectrochemical energy systems that convert the energy locked in organic matter directly into electricity through the metabolic reactions of microorganisms. An MFC consists of two chambers, separated by a semi-permeable membrane. The anode chamber (negative terminal) houses the electroactive bacteria and the cathode chamber (positive terminal) is the counter half-cell that is usually open to air for oxygen diffusion.

Electricity is generated when the microbes consume the organic feedstock for their growth and maintenance, and give-off electrons as a by-product. Consumption of the organic matter means that the microorganisms break down the molecules within, which results in that feedstock being treated or cleaned and is akin to biological trickling filters within municipal wastewater treatment plants. What this means is that MFCs produce electricity whilst treating organic waste, which can be in the form of urine, wastewater or detritus.

This work originated in trying to address the challenge of energy in autonomous systems, and this still drives our motivation to this day. Animals in their natural habitats are agile, resilient, and, most importantly for us, self-sustainable. This has been the source of our inspiration over the years. This is what attracted me to begin my PhD in this cutting-edge area of research and it is because of the EPSRC Career Acceleration Fellowship that we have managed to progress the development of our technology to the level we have today.

Waste potential

MFCs work on bacterial metabolism, which is one of the processes behind bio-degradation. This gives our technology the unique advantage of being one of the very few examples that can be implemented in rural, unconnected or remote environments. Deployment of systems in settings like these is known as 'release and forget', precisely because the (deployed) system has to be energetically autonomous. One example of this has been the family of EcoBots that we have developed over the years, which operate autonomously powered by MFCs and are designed to manage their energy, which comes in the form of organic matter from their environment. This organic matter can be varied, and can include table sugar, prawn shells, rotten fruit, dead insects or urine. This could be a useful gardener for future households, especially if the robot's fuel are pests.

However, the fact that power can be generated from human waste suggests that the same MFC technology can also be integrated with household or community toilets to clean the waste and generate electricity. Therefore this can improve sanitation as well as provide energy to power lights, especially where neither are available. This, which we now call Pee Power®, is part of the Reinvent the Toilet Challenge funded by the Bill and Melinda Gates Foundation and supported by Oxfam, who brought to our attention the reality of refugee camps and slums, where women and young girls face threats every time they need to use the toilet at night. Since July 2017, our Pee Power®/MFC system has been installed at Seseme Girls School in Kisoro, Uganda, and the impact on the pupils since installation has been astounding. The girls now feel safe to use the toilets at night, primarily because perpetrators can no longer hide in the dark.

Benefitting society

Apart from our three consecutive installations at Glastonbury (2015, 2016 and 2017), this has been our first field trial outside of the UK. We would like to see our MFC technology being installed in every environment where there is a real need, whether in sanitation, energy or both. The technology has now reached at Technology Readiness Level 7 and field trials like the one in Kisoro are essential to test our system. Several MFC/Pee Power® installations are being scheduled and the Gates Foundation is fully supporting the commercialisation of our technology, with the appropriate business model, so that it can become available worldwide.

These are the next steps that we are taking in our journey to bring to society a beneficial technology. The progress in the MFC technology development thus far is underpinned by the different engineering fields that are integrated together to achieve this goal. It is precisely the application of engineering knowledge to a scientific problem that is now allowing students at Seseme School to experience improved safety around the everyday environment that we take for granted. And it is this which allows us to think outside convention and envisage smarter robots, vehicles, energy systems, waste processes and cities that can provide a more sustainable future for younger generations.

Year of Engineering

2018 is the Year of Engineering, and throughout the course of the year the EPSRC blog is exploring how engineering touches upon a number of themes, from creativity and inspiration to health and wellbeing.


In the following table, contact information relevant to the page. The first column is for visual reference only. Data is in the right column.

Portrait photo of Professor Ioannis Ieropoulos
Name: Professor Ioannis Ieropoulos
Organisation: University of the West of England