A fascinating oddity in the list of potential alternative power sources is the microbial fuel cell, in which the chemical reactions of micro-organisms digesting their food are harnessed to harvest electrons and thus generate electrical current. We’d like to know more, so [Williamolyolson]’s soil microbial fuel cell is a particularly interesting glimpse into this field.
In this type of cell, an anode is placed at the bottom of a container of anaerobic wet soil medium laced with biomass to provide a food source for the bacteria, and a cathode is placed on the top of the medium exposed to air. The cell in this project appears to be a plastic coffee tub, and the electrodes are copper pan scourers. Unlike a chemical battery they do not need to be different materials and they themselves are not part of the chemistry of the cell, instead, they serve to collect and return the electrons to the cell.
The project logs detail a series of time-series measurements and experiments with placement of the cathode. Yield seems to be in the region of 200mV at about 1mA, though peaks as high as 400mV have been seen. It’s clear that this is not a cell that will replace your grid hook-up any time soon, but it still retains a lot of possibilities for use in micropower applications. There has been plenty of work in the field of micropower harvesting using other sources such as small solar cells, and this has the advantage of microbe-laden dirt being ubiquitous and free.
A couple of previous MFCs we’ve brought you include this multi-cell design said to be capable of charging a phone, and this cell that also supports a fish.
I wonder if you could use this to measure the health of your microorganism or bacterium. For example in a septic tank you can see if the wife has stuck too much detergent in the washing machine and whether you need to assist in order to return the culture back to maximum performance.
You really shouldn’t be draining your wash water into a septic tank. That greywater is perfect for a garden if you have the space.
Well the example would not be much good if you had no reason to monitor the health would it. :)
Unfortunately, depending on where you live you may not be allowed to drain your greywater into the ground. Around here, we have to drain it into the septic system. We use anything labeled or found to be septic safe(r) in regards to maintaining septic tank health. It sucks, but it was code when it was installed.
Hmm, pretty much doubt it unless its highly concentrated destroying basic amino acids – though detergent can definitely change the bacterial mix as does anything you add due to constant activity of shifting equilibria with so many permutations There are about 10million species of bacteria with huge variations in adaptations, some could well convert or exploit detergents as their food or some form of cofactor type biochem to absorb foods etc. I also understand bacteria is the highest mass lifeform on the planet, they are everywhere weighing more than all other life combined. Eg in, on and all around us all the time without respite, worth noting our natural dependency on them for digestion.
FWIW. It’s estimated some 100 or so new species of bacteria are discovered each few weeks or so with some of these previously under the radar whilst some are mutations of earlier species. Adaptations could well be a great area of study in respect of this hackaday post for electrical power as bacteria are fast growing with comparative ease of applying forced adaptations of many types Eg bacteria have been discovered surviving and consuming food in the radioactive pools of nuclear reactors with the suggestion they exploit uranium much like some bacteria exploit iron to catalyse foods for consumption and procreation…
With the success of Craig Venter with synthetic bacterial organisms over a decade ago and others popping up, then I expect it won’t take long to program completely new species of bacteria we can design or amend for far more targetted processes such as pushing electrons around, there are all sorts of ways to do this too some in conjunction with yeasts eg for making diesels and other liquid fuels then you just need a fuel cell Or even combine them. Thanks for posting and comment :-)
I am always somewhat skeptical of these microorganism “power sources”, that what they are seeing is not related to the microorganisms per se, but is essential a battery with the soil as an electrolyte… do they have control cells without microorganisms, but all the other salts, soil and media as a control?
Or using non-reactive electrodes. Graphite for example.
Or same type of electrode on both, so that it cancels out.
If you can’t do an A/B test swapping out electrodes without affecting the output open circuit voltage, then it is just a battery with some ‘organic’ part in the electrolyte.
Look at yeast for an example of a single-celled microorganism, they take sugars and water and produce ethanol and carbon dioxide which bubbles out of the liquid. Surely the chemical reaction driven by a microorganism have at least the potential to generate some kind of voltage difference between the bottom and top of the material involved.
Microbial Fuel Cells have been about for a 50 plus years, I seriously doubt that a control test was not done with the same material in multiple cells where the control was fully sterilised with say a UV-C germicidal light. There have been a lot of papers published on MFC’s, it is almost inconceivable, that it was not done.
so the power output is smaller than what you’d get from a peltier stuck to a compost pile?
So, the copper doesn’t kill the organisms?
Unconvincing until he shows that dumping some formaldehyde into it kills the germs along with the power. Until then my bet is on some galvanic process.