Microbial Fuel Cells

Yesterday, my TV remote stopped working. Its batteries had died. I feel bad every time this happens. Used batteries make toxic junk. Also, a dead remote reminds me how much my lifestyle depends on electricity! 

Many common energy sources and technologies are fraught with problems. We use a lot of non-renewable fuels to generate electricity. For example, we use coal, oil and natural gases to generate electricity. But these will eventually run out. In the meantime, they mess up the environment. They cause air pollution and climate change.

We need smarter alternatives. We need renewable energy sources. And we need 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. Some bacteria produce their own energy. They do this through a process called anaerobic cellular respiration. Anaerobic means “without air.” These bacteria typically live in a low-oxygen environment. You may be familiar with the process of photosynthesis. During photosynthesis, plants turn carbon dioxide and water into the sugars they use for energy. Cellular respiration is essentially this process in reverse. It breaks down sugars into water, carbon dioxide and (most importantly) adenosine triphosphate (ATP). ATP is the energy molecule that all cells need to function. 

The chemical formula for cellular respiration is:

Scientists have found a way to capture the energy that cellular respiration creates. They do this with a technology called a microbial fuel cell (MFC). 

Did you know?

The English botanist M.C. Potter was the first person to generate electricity from bacteria. He generated electricity from E. coli back in 1911! 

How do batteries generate electricity? 

How do MFCs work? First, let’s look at how an ordinary dry cell battery works. A battery generates electricity using chemical energy. In a battery, one of the electrodes (the anode) undergoes an oxidation reaction. This is a chemical process that gives off electrons. The electrons travel through a paste of manganese oxide to the other electrode (the cathode). Here, the electrons undergo a reduction reaction. This is a chemical process in which electrons are absorbed. As the electrons move from anode to cathode, they create an electric current. This can do work, such as power a light bulb.

How are MFCs different from ordinary batteries? 

Just like an ordinary battery, an MFC uses chemical energy to generate electricity. An MFC has two electrodes held in separate chambers. The anode chamber that contains the bacteria is anaerobic. This means that it does not contain oxygen. The cathode chamber is aerobic. That means it does contain oxygen. The oxidation process occurs inside the bacteria living in the anode chamber. This takes advantage of the oxidation that bacteria carry out naturally during cellular respiration. Electron bonds hold together the molecules in the food that bacteria eat. The bacteria break those bonds to release the electrons.

Cellular respiration can continue for as long as the bacteria have food. Bacteria can digest pretty much anything. They can digest human waste. They can also digest other waste products such as ammonia, ethanol, or acetate. This makes MFC technology really attractive. It can generate electricity and get rid of waste at the same time! 

Generating electricity using 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? The design and materials used to build the electrodes have greatly improved. But MFCs still generate relatively low currents. Why? One reason is that electrons given off during cellular respiration don’t transfer well from the bacteria to the anode.

Bacteria used in MFCs are called exoelectrogens. They are electrochemically active and can transfer electrons outside their cells. The electrons they give off reach the anode in 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. MECs use outside power to produce fuel, such as hydrogen.

What is the future of MFCs? 

One day, MFC technology could be used to generate power with biodegradable waste and sewage. At the same time, it could provide help with wastewater treatment and bioremediation. MFCs could also help monitor the amount of biodegradable material left in wastewater streams. They could also help with remote sensing. These tasks could be done by self-powered devices using MFCs. 

Did you know?

Researchers are also exploring whether MFC technology could power equipment in space. 

Could these natural mechanisms be enhanced? Scientists are trying to answer this question using genetic engineering. They manipulate the genes involved in the electron transfer. They also manipulate other genes key to the life cycle of bacteria. 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. This is clearly not an option in a TV remote.

Summing up

Will bacteria one day generate some electricity you use? It is very possible. This electricity generation process might help deal with waste. It may even help clean up contaminated soil and water. This is just one among several new alternative energy sources. Energy generation in the future might be much cleaner and more sustainable than today.