Scientists have published the world's first research paper on work that tested the viability of urine as a potential fuel for Microbial Fuel Cells (MFCs) in order to directly produce electricity.
Dr Ioannis Ieropoulos, Professor John Greenman and Professor Chris Melhuish (Bristol Robotics Lab, UWE Bristol) have outlined research carried out to look at whether urine could be used as a fuel by the MFCs and how much power could be generated by MFCs using urine in this way.
MFCs consist of two half-cells - an anode and a cathode - that are separated by an ion selective membrane. Commonly bacteria are in the anode side, and chemicals or oxygen are in the cathode side, which complete the reactions (i.e. close the circuit) to generate power.
So far the use of urine as a biomass that can be converted to power via MFCs has been neglected by scientists, despite the fact that urine is an abundant waste product. Each human produces approximately 2.5 litres of urine a day, amounting to around 6.4 trillion litres globally each year.
Dr Ioannis Ieropoulos explains, "Urine is chemically rich in substances favourable to the MFCs. Our research found that the output of electricity was consistent and measurable depending on the volume of urine and the timing of the doses. At the moment the output from one MFC is small. Through this study and the related work carried out by our group over the years, we were able to show that by miniaturisation and multiplication of the number of MFCs into a stack and regulating the flow of urine, it may be possible to look at scales of use that have the potential to produce useful levels of power, for example in a domestic or small village setting.
"A stack consists of a number of MFCs, each just a few millilitres of volume, connected together so that the stream of urine runs through the MFCs and produces power as the microbes inside the MFCs get to work on this abundant fuel, which is rich in (amongst other things) carbohydrates, nitrogen, potassium, phosphorous and other organic compounds that collectively make it very good for the microbial fuel cells."
As well as urine production from humans, farm animals worldwide produce around 2 - 3 times as much urine as humans, adding up to approximately 38 billion litres a day. The scientists suggest that by scaling up MFCs into stacks, further research might bring the levels of electricity production closer to those currently produced by biofuels.
Urine produced by farm animals can have a significant knock on effect on the environment. The advantage of an MFC system that uses urine - whether human or animal - is that the process within the MFCs effectively 'cleans' the urine so that it could safely be discharged into the environment, removing the need for conventional treatment by wastewater companies.
Dr Ieropoulos says, "Whilst we recognise the need for a great deal more research in this area, we are very excited by the potential of this work.
“This is the first paper to outline not just the use of urine as a potential fuel for MFCs, but also the fact that urine could be an abundant source for electricity generation. The impact of this could be huge, since it enables us to think of 'waste' in a new way, and offers great potential for the future and we are grateful to the EPSRC for funding this work."