Science Buddies: "Ask an Expert"

Hello, so my son is doing an experiment similar to waste not, want not with a MFC. We have used soil and built two MFC’s. They seem to be working but have run into bleep that is puzzling us. We are using air pumps as suggested to increase the voltage when we take readings but instead of increasing the voltage when the pumps are on, the voltage decreases. When we unplug the pumps the voltage goes back up.We have used a battery to check the voltage and make sure our multimeter is reading properly. Any help would be much appreciated. Thank you

Hello Anarqus,
The project sounds interesting as a variant of another project, and because of that can you expand more on the details of the projects. Is there any online direction? From what I understand, the electrical current has been reversed. Unintentional opposite wiring can cause this. Can you check again with reverse wiring?

Please tell us more about the situation, and I hope this helps.
BT

Thanks a lot for the reply. Yes we combined a couple different projects. It does seem like a wiring reversal. Both MFC’s are set up exactly the same. A cathode in the soil and an anode in a water solution.we just have copper wire coming from each. In any other MFC experiment we have researched applying air to the water solution causes voltage increases but on ours the voltage decreases. When we turn off the air pump our voltage comes back to what it was.

Hi anarqus,

How are the air pumps connected to the MFCs? Can you provide a link to the directions that suggested this? I don't think any of our MFC projects at Science Buddies use air pumps (I could be wrong). One guess could be that the pumps are causing air bubbles to get in between the mud/water and the electrodes, which could decrease the voltage. That is just a guess though, since I am not familiar with how the pumps are connected.

Thanks,

Ben