Don’t flush it!

Every one of us will produce enough urine each year to fill two bathtubs — some 135 gallons. But instead of flushing it down the toilet, why not do something more useful with it? And that is exactly what scientists at the University off Bath have done. They’ve developed a miniature fuel cell that can generate electricity from urine. The applications are endless and it is an affordable, renewable and carbon neutral way of generating power. The new cell is cheap, costing just £1-£2 to produce, and its creators hope it will provide a way of producing energy in remote areas.

What is a microbial fuel cell (MFC)?

A microbial fuel cell is a device that uses natural biological processes of ‘electric’ bacteria to turn organic matter, such as urine, into electricity. These fuel cells are efficient and relatively cheap to run, and produce nearly zero waste compared to other methods of electricity generation. In this case urine will pass through the microbial fuel cell for the reaction to happen. From here, electricity is generated by the bacteria which can then be stored or used to directly power electrical devices. Other forms of waste, such as sewage, waste water and earth can also be used to generate the reaction.

How much energy

Currently, a single microbial fuel cell can generate 2 Watts per cubic metre, enough to power a device such as a mobile phone, but work is ongoing to improve their capacity. Dr Mirella Di Lorenzo, a lecturer in the University of Bath’s Department of Chemical Engineering and corresponding author, said: “If we can harness the potential power of this human waste, we could revolutionise how electricity is generated. Microbial fuel cells can play an important role in addressing the triple challenge of finding solutions that support secure, affordable, and environmentally sensitive energy, known as the ‘energy trilemma’.”

The new technology has been used to fuel the lighting in a prototype toilet at the University of Bath, sponsored by Oxfam Pioneers. The charity is now going to test this innovation in an emergency setting and is involved in develop the technology further to create stack of cells to provide enough power to light a 10 metre radius around a block of four toilets.

Already in use

One company leading the field commercially is Israeli based Emefcy. It builds spirally wound aerobic biofilm reactors which use MFC for waste treatment plants. Its reactors need as much as 90% less energy to run and reduce the amount of excess sludge by 30%-50% compared to conventional processes. In addition the electricity produced by the reactors can be used to power the plant itself.

Another firm, US based Cambrian Innovations, specialises in producing clean water and energy using waste water produced by the food and drinks production industry. Matt Silver, chief executive officer at Cambrian claims its EcoVolt systems can produce as much as 80,000 gallons of treated water a day, reduce fresh water consumption by 40%, eliminate 1,600 metric tons of carbon dioxide emissions annually, and use the methane created to produce as much as 130 kilowatts of power.

Out of this world

MFCs are also on their way to space. The Naval Research Laboratory (NRL) has begun work on a prototype rover that is part powered by a bacteria known for breaking down metals. The NRL plans to use a hybrid MFC/battery system to power a smaller 1 kg hopping rover. The MFC would be used to power low load devices such as electronics and sensors, while the battery would be used for higher power loads, including movement.


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