A Clock Powered by Flies? Microbial Fuel Cells Turn Poop into Power


Energy is a longstanding problem.  The energy crisis is not just the sinusoidal prices at the pumps and a reluctance to build wind farms in pristine natural environments; it affects every single person on this planet.  From the U.S. citizens who stuff old, liquefied fossils into their inefficient gas-guzzler to the poorest of villagers in Africa who struggle to find firewood in a rapidly deforesting continent, everybody is affected.  Energy has to come from somewhere and a team of researchers at the University of Bristol in the UK thinks they have a solution that might help alleviate some of the crisis.

A real functioning microbial fuel cell clock from Beihang University

The idea is called the Microbial Fuel Cell, and the principle behind it is quite simple.  A biological material is placed into a medium of microbes and is slowly digested.  The digestion process creates spare electrons that would normally just recombine with ions.  But in the fuel cell design, those electrons are sent through a circuit before being recombined and powering electronics in the process.

There are quite a few possible applications for such a design.  Really, anything that needs power can be run off of a microbe fuel cell, but there are a few novel ideas floating around the internet that apply the fuel cell technology without the need to stand around and constantly feed organics into the system.  Wastewater treatment has been targeted as an ideal way to scale up the system, using a feedstock that is high in unwanted organics, and creating energy while simultaneously purifying the water.

This automated fly trap is designed to feed a bio-fuel clock

On the smaller scale, ambitious students at the Royal College of Art in London have dreamed up a way to use the microbial fuel cell technology to take care of a common nuisance: flies.  They envision using rotating flypaper to catch flies and scrape them into the microbial fuel cell, which will then turn the airborne pests into fuel to power the flypaper rotation as well as a clock or light.

Though neat, there are quite a few issues with a design like this.  Firstly, the open system will allow microbes to flow freely in and out of the device and chances are the strain of fly-eating microbes are probably not very friendly towards humans or pets either.  Secondly, there is always an optimal condition for microbial growth, so the digestion chamber would likely need to be heated and pH balanced.  Such a design would make it near impossible to have good enough process control measures to sustain microbial growth for more than a few hours, no less an infinite period of time.  These issues, however, are easily fixed on the large scale, industrial processes which could lead the microbial fuel cell to have a serious effect on the future of energy production.

The idea of using microbes to get energy is not a new one.  Fermentation, one of the oldest tricks in the proverbial book, has been to make beer for centuries: utilizing strains of yeast to create alcohols.  Even today, fermentation plays a huge role in the production of many chemicals and drugs including automotive grade ethanol.  The microbial fuel cell, however, is a bit different.  In most fermentation processes, cellulosic materials are broken down into flammable chemicals that are then burned for energy.  But in the fuel cell, there is no combustion or the associated thermodynamic losses.

A biogas-producing wastewater treatment plant

It is obvious that digested flies and poop cannot create enough power to keep every television and light bulb in America running, but such a method of harvesting essentially free energy would do well to help reduce consumption.  Anaerobic digestion is already used in some wastewater treatment plants to create a flammable biogas that is burned for energy.  The microbe fuel cell could possibly help move the wastewater treatment industry from necessary expenditure to power generator.  The idea is quite a few years off from being retrofitted into every existing treatment plant, but even the thought of a fly powered clock is enough to pique our interest.

Andrew is a recent graduate of Northeastern University in Boston, MA with a Bachelor of Science in Chemical Engineering. While at Northeastern, he worked on a Department of Defense project intended to create a product that adsorbs and destroys toxic nerve agents and also worked as part of a consulting firm in the fields of battery technology, corrosion analysis, vehicle rollover analysis, and...

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