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One Pot Plant Microbial Fuel Cell

One Pot Plant Microbial Fuel Cell

by gal.schkolnik xumium | updated May 19, 2016

A membraneless plant microbial fuel cell (MFC) with mud-embedded anode and air cathode.

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What and why (or introduction)

tl;dr When out of oxygen, electroactive bacteria found in mud transfer their metabolic electrons to an electrode, creating electrical current. A water-plant can supply them with sugar to fuel this process. If we build the right setup for that, we can get plant-pot batteries.

More details: Electroactive bacteria, found mainly in anoxic environments (in nature: lake sediments; in human settings: wastewater), can perform extracellular electron transfer (EET). This means that when out of soluble electron acceptors (or donors), they can transfer metabolic electrons over their cell membranes to insoluble ones. In nature, such insoluble electron acceptors (or donors) can be metal oxides (or metals), such as rust (or iron). In the lab, they can be positively (or negatively) poised electrodes.

Microbial fuel cells (MFC) are batteries where bacteria are supplied with organic food molecules, such as sugars or acetic/lactic acid, and with a positively poised electrode, aka anode, serving as electron donor and acceptor, respectively. The circuit is closed by an air cathode, where the electrons donated by the bacteria are used for oxygen reduction. This way, potential and current are formed, i.e. the bacteria help us produce electrical power from organic compounds that they eat. Supplying bacteria with an insoluble electron acceptor in anaerobic environments can greatly facilitate wastewater treatment.

In a plant-MFC, a plant which shares the habitat with the bacteria releases excess sugars from its photosynthesis to the soil, thus feeding the bacteria. This way, you can get higher power outputs in a very easy to build continuous system. To avoid using a membrane or two pots for separating the anode and cathode chambers, here we bury the anode in the sediment, in the hope to achieve oxygen stratification resulting in an anoxic environment around the anode.

Each plant pot should yield 500-700 mV and around 1mA, and when a few are connected the result can be a sustainable, nearly carbon neutral battery. Depending on the number of MFC plant pots connected, this can serve for powering a low-power appliance.

How (or materials and methods)

  • We buried fine stainless steel wool (image bottom right) at the bottom of a polyethylene container and attached one side of a two-crocodile wire to it.
  • We added mud from the anoxic zone at the edge of the water (depth ca 15 cm) in Weissensee, Berlin, and agitated it so that the mud penetrated the stainless steel wool. We allowed the mud to settle for ca. 30 min, then carefully placed washed aquarium gravel (carrera-split, 9-12 mm, Hellweg, Berlin, image top right) on top of the mud layer. We added dionized water to the gravel.
  • The next layer was aquarium filter carbon (Eheim, Deizisau, Germany, image top left).
  • We stuck a plant cutting stem (Devil's Ivy, muahahaha!) through two coarse stainless steel sponges (image bottom left) and placed this on top of the activated carbon and added more activated carbon on top, so as to fill the gaps in the sponge, and more dionized water to cover the sponge.
  • The crocodile coming from the anode (bottom steel wool) was connected to a 1000 Ohm resistor and from there another two-crocodile wire was used to connect the resistor to the cathode (top steel sponge).
  • This was done in duplicates named Ada and Bertie.

May 14, 2016 at 11:37 AM
Created by xumium and gal.schkolnik
Comments (2)
Wow, what do you expect this to be able to power?
7 months ago
One plant pot could potentially give us 500-700 mV and around 1mA (hard to tell though, because we haven't estimated electrode surface areas). If we connect the two in series, it might be enough for a clock, pocket calculator or maybe even a LED. But we'll have to wit and see first...
7 months ago

​Ada and Bertie serially holding hands. Combined potential: 194 mV.

Bertie has a potential drop of 97.1mV, current 0uA

​​Ada has a potential drop of 95.4 mV, current 0uA.​

May 14, 2016 at 11:42 AM
Created by xumium
Comments (0)