MAR 24, 2017 1:21 PM PDT

The power of microbial fuel cells

WRITTEN BY: Kerry Evans

A microbial fuel cell is exactly what it sounds like, a fuel cell powered by microbes.

I have to admit, I’d never heard of a microbial fuel cell until recently (or maybe I had, but it just didn’t register).

The first microbial fuel cell (MFC) was rigged up by M.C. Potter way back in 1911 - this MFC used E. coli to generate electricity. Unfortunately, the idea didn’t gain much traction until the 1970s. At that time, Robin M. Allen and H. Peter Bennetto put their heads together to figure out how MFCs actually work.

Very simply, an MFC uses bacteria to convert chemical energy to electrical energy. In many MFCs, that chemical energy is glucose. When bacteria metabolize glucose under aerobic conditions, they produce carbon dioxide and water. However, under anaerobic conditions, they produce carbon dioxide, protons, and electrons. The electrons are the key to an MFC.

A simple microbial fuel cell - Trends in Biotechnology

The generic MFC has one chamber containing bacteria and an anode. The anode is connected by a wire to the cathode in a neighboring chamber. The electrons pass from the bacterial electron transport chain to the anode. (There are a number of ways to transfer electrons from the bacteria to the anode, but I won’t bore you with the details.)

The cathode chamber can simply contain air (assuming your air contains oxygen). Here, the oxygen acts as the electron acceptor - electrons leave the cathode and combine with oxygen to produce water. (Yes, this also requires hydrogen ions. These are also produced by the bacteria and can cross a membrane or salt bridge that separates the anode and cathode chambers.)

The basic MFC I’ve just described is called a “mediator-free” MFC. This means that the electrons are passed directly from the bacteria to the anode - they don’t need a mediator. (Various chemicals can be added to the anode chamber to act as mediators.)

Mediator-free MFCs are way more cool that mediated MFCs. They use so-called electrochemically active bacteria that transfer electrons directly to the anode. Many of these bacteria produce pili or “nanowires” to shuttle electrons from their outer membrane to the anode. (Yes, this is as cool as it sounds.)

MFCs can run on a number of chemical energy sources, but my favorite has to be soil. In its simplest form, a soil-based MFC uses soil as the anode. The soil provides the bacteria, the chemical energy source, and acts as the medium for proton exchange (how convenient!). Simply place your anode down in the soil, and leave the cathode at the surface, exposed to the air. You can even build your own soil-based MFC at home!

Okay, are these MFCs just a fun party gag? Or could they really be used to generate electricity on a large(ish) scale?

It turns out that MFCs are quite widely applied to wastewater treatment. These systems generate energy in the process of decontaminating wastewater. How about the oil and gas industry’s wastewater? That stuff contains lots of hydrocarbons and lots of salt. The hydrocarbons can be metabolized by bacteria, producing electrons that power desalination!

Thanks, bacteria!

Sources: Environmental Science and Technology, New Atlas, Pennsylvania State University, Wikipedia

 
About the Author
  • Kerry received a doctorate in microbiology from the University of Arkansas for Medical Sciences.
You May Also Like
MAY 11, 2020
Microbiology
Bacteria Can Tumble Their Way Out of Traps
MAY 11, 2020
Bacteria Can Tumble Their Way Out of Traps
We share the world with vast numbers of microbes, many of which are able to move around freely in the environment. Most, ...
MAY 15, 2020
Immunology
Support the Microbiome So the Immune System Can Do Its Job
MAY 15, 2020
Support the Microbiome So the Immune System Can Do Its Job
Research has long connected the human microbiome and immune system function, and now a recent study pinpoints a key poin ...
JUN 01, 2020
Genetics & Genomics
Vaping Increases Oral Disease Risk After Only a Few Months
JUN 01, 2020
Vaping Increases Oral Disease Risk After Only a Few Months
E-cigarettes have emerged as a healthier alternative to smoking, but many studies have suggested that vaping still poses ...
JUN 29, 2020
Microbiology
Childhood Vaccine May Help Prevent Severe COVID-19 Cases
JUN 29, 2020
Childhood Vaccine May Help Prevent Severe COVID-19 Cases
Vaccines that contain live attenuated viruses may be giving people some protection from serious cases of COVID-19 that i ...
JUL 26, 2020
Microbiology
Ongoing Salmonella Outbreak Rapidly Spreads to 23 States
JUL 26, 2020
Ongoing Salmonella Outbreak Rapidly Spreads to 23 States
The CDC has announced that an outbreak of infections related to a strain of the bacterium Salmonella is "rapidly growing ...
JUL 28, 2020
Microbiology
After 100 Million Years Under the Seafloor, Ancient Microbes Come Alive
JUL 28, 2020
After 100 Million Years Under the Seafloor, Ancient Microbes Come Alive
It has been said that we know more about the moon than we do about the bottom of the ocean, though explorers and researc ...
Loading Comments...