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.
Alchemists tried in vain to transmute lead into gold. What if you could turn waste products into energy? That’s what [chemicum] did in a recent video–he and some friends built microbial fuel cells that convert excrement into electricity (you can see the video, below).
The video doesn’t give you all the details of the build, but it seems easy enough. You need some stainless steel mesh, some activated charcoal, some epoxy, plastic containers, and some assorted metal plates and hardware. Of course, you also need excrement and–if the video is any indication–some clothespins to clamp your nose shut as you work.
Move over, potato batteries: DIY microbial fuel cells are here to stay! A microbial fuel cell (MFC) is a device that uses bacteria in an anaerobic (oxygen-poor) environment to convert chemical energy into electricity. [drdan152] posted steps on how to make a soil-based MFC with a neat twist: it’s also a fishbowl for a betta fish.
[drdan152] used soil from the wetlands, referred to as “muck.” This nutrient-rich soil provided a hearty supply of bacteria, especially Geobacter species, known for their uncanny ability to transport electrons outside their cells using bacterial nanowires. The proton exchange membrane (PEM) was made up of salt, water, and agar. After some initial runs, [drdan152] determined that flat char cloth made the best anode, while red copper wire served as the cathode. Assembling the MFC was as simple as surrounding the anode with a thick layer of muck on all sides, adding the PEM on top, followed by water. The cathode was situated halfway out of the water.
After a couple of days, the voltage increased in proportion to the amount of bacteria growing on the anode. The betta fish can happily live in this habitat for a short period of time(it still has to be fed, of course), and the bacteria certainly won’t mind – the fish’s excrement provides an additional food supply. As a bonus, the water is kept clean. However, like any aquarium, the water will need to be changed periodically as carbon dioxide byproduct accumulates from the fish’s respiration and the MFC (high carbon dioxide levels = dead betta fish).
The MFC generates 725 mV. [drdan152] is not satisfied with that number, and is testing out charge pump circuits to generate as much as 3V. We are looking forward to seeing the results. We also wonder if a small aquatic plant could help make it a more self-sustaining environment for the fish. In the meantime, [drdan152] is encouraging others to try larger-scale versions of this MFC. Perhaps MFC-poweredcarnivorous robots doubling as mobile aquariums are in our near future.
Imagine our surprise when this article on Ecobot III and the disgusting video above showed up in our feed. The robot can theoretically be self-sustaining forever, so long as it has a food source. Yes, you read correctly, food.
Typical robots relying on grub burn the biomass to produce heat/steam/energy, but Ecobot III actually digests using Microbial Fuel Cells and extracts energy in the form of hydrogen.
The process isn’t very efficient (yet), and of course waste must be excreted, but we’re inching closer and closer to the day our robot overlords are invincible. The project has come to a halt (we can’t imagine why), but you can still read up on the process, and meet Ecobot’s brothers: II and I.