Microbial Fuel Cell with a Side of Betta Fish

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-powered carnivorous robots doubling as mobile aquariums are in our near future.

Building an aquarium into your walls

built-in-aquarium

We looked through the build log for this in-wall aquarium and were a bit horrified by the before pictures. You look at the original basement photo and there’s wood paneling, an incredibly rusty plumbing stack, and good god what is that wire jumble hanging from the ceiling? But the project’s not about building codes, it’s about the infrastructure that supports this fish tank.

This corner of the basement has a window and the electrical panel in it. It needs to be this big in order to enclose that window, but that offered the opportunity to add in the aquarium while still allowing easy access for feeding and cleaning. Hot and cold water pipes were run over to the location for easy filling. There’s even a drain line running to a utility sink in a different part of the basement for easy cleaning.

This seems like a bit of an upgrade when compared to the coffee pot fish bowl.

[via Reddit]

Automated aquarium fertilizer doser

aquarium-auto-doser

If you are using live plants in your aquarium you must remember to fertilize them at regular intervals. Being a bit forgetful, [Deven] automated the process by building this auto-doser.

There are three different chemicals which are dispensed by the system. They are stored in the drink bottles seen above. Each has a plastic tube which runs up to the dosing motors mounted on the black box. [Deven] sourced the motors from eBay. They are designed for this type of application.

Inside the black box is the Arduino that handles timing and switches the motors. The control circuitry is protected using one MOSFET for each. To keep the fish safe the outflow is directed right into the aquarium pump so that the concentrated chemicals are quickly dispersed through the entire tank.

Now that he’s made it this far he might as well add the ability to feed the fish and control the lighting.

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Scavenged tube television makes a nice fish tank

aquarium-from-junked-television-set

[McCaulsey] found an old TV waiting for garbage pick-up on the side of the curb. He brought it home and gave it a new life as an aquarium.

His technique is a little rough, but the finished look is exactly what he was going for. He picked up the cheapest aquarium set he could find at the pet store. It just happens to have a curved front to it which helps to recreate the look of the original CRT. After removing most of the electrical components he went to work on the plastic fins that were used to mount them. Having somehow misplaced his Dremel tool the work was done with a drill and a 1/4″ paddle bit.

Once the demolition was over he started the rebuild by placing a backer in the tank. This is an underwater image that will save him from having to look at the inside of the TV case through the water. A piece of Styrofoam was used as a base to properly frame the front of the tank. The only thing we can’t tell from the build album is how he will manage to feed the fish without taking everything apart again.

[via Reddit]