Above: A diagram of a soil-based microbial fuel cell (Wikimedia Commons/MFCGuy2010)
Yesterday, my TV remote stopped working. Its batteries had died. I feel bad every time this happens, and not just because used batteries make toxic junk. It also reminds me how much my lifestyle depends on electricity! Many common energy sources and technologies are fraught with problems. Non-renewable fuels used to generate electricity—like coal, oil and gas—will eventually run out. In the meantime, they mess up the environment, causing air pollution and climate change.
Did you know? The first microbial fuel cell (MFC) was built in 1911 by English botanist M.C. Potter. It was the result of his investigations into how microbes break down organic matter to obtain energy. What’s needed are smarter alternatives: renewable energy sources and technologies that are friendlier to the environment. One of these smart alternatives could come from the oldest, smallest, and most adaptable creatures on the planet: bacteria.
Like all living cells, bacteria need energy. They get it from food using their own power generating process, called cellular respiration. And scientists have found a way to capture this energy through a technology called the microbial fuel cell (MFC).
Just like an ordinary battery, an MFC has two electrodes held in separate chambers, and it makes electricity from chemical energy. One of the electrodes (the anode) undergoes oxidation. This is a chemical process that gives off electrons packed with energy. The electrons travel through a wire to the other electrode (the cathode). Here, they participate in reduction, a chemical process in which electrons are absorbed. As they move from anode to cathode, the electrons do work, such as power a light bulb.
Electrifying waste water: Using microbial fuel cells to generate electricity (2013)
Bruce Logan, The American Chemical Society
The main difference between MFCs and ordinary batteries is that the oxidation process occurs inside bacteria living at the anode. This takes advantage of the fact that bacteria carry out oxidation naturally during cellular respiration. The molecules they eat are held together by electron bonds, and the bacteria break those bonds to release the electrons.
Cellular respiration can continue for as long as the bacteria have fuel, in the form of food. What kind of food? Actually, bacteria can eat pretty much anything, including human wastes and residues such as ammonia, ethanol, or acetate. This makes MFC technology really attractive because at the same time as it generates electric power, it can also clean up our junk.
Drawing electric power from bacteria is not a new idea. In fact, it’s been around for over a century. So why hasn’t MFC technology delivered on its promise yet? Although the design and materials used to build the electrodes have greatly improved, MFCs still generate relatively low currents. A big reason for this is that electrons given off during cellular respiration don’t transfer well from bacteria to the anode.
Bacteria used in MFCs are called exoelectrogens, and the electrons they give off reach the anode via one of three ways:
1. They can be transported by protein carriers on the cell surface.
2. They can be exported through cell membrane projections (nanowires).
3. They can be secreted in chemical solutions (mediators).
Did you know? Microbial electrolysis cells (MECs) are a type of modified microbial fuel cell (MFC). MECs use outside power to produce fuel, such as hydrogen. Could these natural mechanisms be enhanced? Scientists are trying to answer this question using genetic engineering. By manipulating the genes involved in the electron transfer, as well as other genes key to the life cycle of bacteria, they hope to increase the performance of MFCs. This line of research is still young but holds a lot of promise.
So will MFCs power my TV remote in the future? Probably not. Unlike ordinary batteries, MFCs require a constant inflow and outflow of materials. In particular, they need a steady supply of food for bacteria at the anode, which is clearly not an option in a TV remote.
However, it is very possible that MFC technology could be used to generate power using biodegradable waste and sewage. At the same time, it could provide help with wastewater treatment and bioremediation. Self-powered devices for monitoring the amount of biodegradable material left in wastewater streams and for remote sensing could probably also use MFCs. Researchers are also exploring the possibility of using MFC technology to power equipment in space.
Within a few decades, it is very possible that some of the power you use will be generated by bacteria. Producing this electricity may also help deal with waste while cleaning up contaminated soil and water. And since this is just one among several new alternative energy sources, chances are that energy generation in the future will be much cleaner and more sustainable than today. Does that mean I should stop worrying about my dependence on electricity? What do you think?
Websites with general information on microbial fuel cells:
Scientific article and websites with information on research into making microbial fuel cells more powerful and efficient: