Urine: flush or fuel?

Developing microbial fuel cells to turn one of our biggest waste products into electricity

Co-author Jon Chouler is a PhD candidate in the Department of Chemical Engineering at the University of Bath.The average person produces between 800ml and 2,000ml of urine every day. Multiply that 7 billion times, and you end up with a huge volume: between 560 billion and 1.4 trillion liters of urine a day – down the drain.

What if that wasn’t wasted but instead used as a fuel?

Energy comes at a premium today. We are running out of fossil fuels at an alarming rate, and when we do burn them, we’re adding more and more greenhouse gases into the atmosphere, contributing to climate change. There’s increasing pressure for us to find new sustainable sources of energy, and bioenergy is one option.

It’s possible to produce bioenergy through processes like anaerobic digestion, fermentation and gasification. These are often carried out at large scale and can require high temperatures and pressures. Another option is microbial fuel cells, which turn organic matter into electricity by harnessing the natural processes of bacteria. They’re efficient, relatively cheap to run and produce less waste than the other methods.

Microbial fuel cells have real potential to produce renewable bioenergy out of waste matter like urine. Considering the huge volume of urine we produce, if we could harness its potential power using microbial fuel cells, we could revolutionize the way we make electricity.

Overcoming limitations of microbial fuel cells

Co-author Mirella Di Lorenzo, PhD, is an Associate Professor in the Department of Chemical Engineering at the University of Bath.So why aren’t we all using microbial fuel cells? One reason is they can be expensive to manufacture. Microbial fuel cells feature electrodes that collect the positive and negative charges that result from the bacteria breaking down the urine, turning the charge into electricity. The negative electrode – the cathode – often contains platinum to speed up the reaction, making the device cost more.

Also, microbial fuel cells tend to produce less power than the other methods of bioenergy production. It’s preferable for them to be smaller and therefore portable, but this limits their power output.

We collaborated with colleagues at Queen Mary University of London and the Bristol Robotics Laboratory to come up with a new design to overcome these limitations, which we present in our paper in Electrochimica Acta.

Our new miniature microbial fuel cell uses no expensive materials for the cathode; instead it’s made of carbon cloth and titanium wire. To speed up the reaction and create more power, it uses a catalyst that’s made of glucose and ovalbumin, a protein found in egg white. This is particularly interesting for developing countries, especially impoverished and rural settings, as it means the microbial fuel cells are cheaper and more sustainable to produce.

Microbial fuel cells used in this study. (The image was featured in the original research article by Jon Chouler et al in Electrochimica Acta, February 2016)

We then played with the design to see how we could produce more power. By doubling the length of the electrodes, from 4mm to 8mm, we could increase the power output tenfold. And by stacking up three of the miniature microbial fuel cells, we were able to increase the power tenfold compared to the output of individual cells.

This is a step in the right direction. Our new design is cheaper and more powerful than traditional models. Devices like this that can produce electricity from urine could make a real difference by producing sustainable energy from waste.

Read the study

This article is published open access:

Jon Chouler et al: “Towards effective small scale microbial fuel cells for energy generation from urine,” Electrochimica Acta, (February 2016).

The journal

Electrochimica Acta is the official journal of the International Society of Electrochemistry (ISE). The journal covers disciplines within electrochemistry, including analytical, molecular and physical electrochemistry, bioelectrochemistry and electrochemical energy conversion and storage. The ISE was founded in 1949 by leading European and American electrochemists to serve the growing needs of electrochemistry. Since then the ISE has evolved to comprise more than 2000 individual members, from more than 60 countries.

Elsevier Connect Contributors

Dr. Mirella Di Lorenzo has been an Associate Professor in the Department of Chemical Engineering at the University of Bath, UK, since July 2011. She is a chemical engineer with a PhD in industrial biotechnology. Her research interests regard the design and development of bioelectrochemical devices for energy harvesting, water quality monitoring and wearable sensors for healthcare.

Jon Chouler is a PhD candidate in the Centre for Sustainable Chemical Technologies, funded by the Engineering and Physical Science Research Council (EPSRC), within the Department of Chemical Engineering at the University of Bath, UK. Jon graduated from the University of Bath with a MEng in Chemical Engineering, which included a year-long placement working for Procter and Gamble in process improvements for dish homecare manufacturing. The focus of his PhD work is the development of a cost-effective and self-sustaining microbial fuel cell, not only for generating energy from waste, but also to be used as a water quality monitoring tool.

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