Science Buddies: "Ask an Expert"

Hello,

The title of my project on science buddies is https://www.sciencebuddies.org/science- ... p071.shtml. I made a microbial fuel cell and I have been measuring the power output with a multimeter. Since yeasterday all of a sudden the highest resistors started to get a higher voltage reading and all the others started to decrease unlike before the day before I had added salt and the reading today just dropped all across unlike before.

I just wanted to know if it matters what resistor I started with on the procedure on science buddies said to start with the largest. But I just wanted to make sure that is correct. In case it effects the outcome.

Also my cathoad started split in half yeasterday could that possibly effect it at all.

Also how could I possibly repair my cathoad without having to buy a new one its just like a sponge. Could I glue it without it affecting the bacteria in the microbial fuel cell?
Or could I sak my mom to knit it with yarn?

Hi,

One word of advice before we start—please keep ALL your posts in one thread so other experts can find everything in one place. I had to scroll down through a dozen posts to find your previous one.

What happened with your meter? Did you take it to RadioShack to test it? Was it faulty? We need to know if it was. Are the hacker boards working ok?

I’m not sure I understand what you are aasking about the voltage readings. The resistors with the highest ohms (4670, 2190, 1000) should give a voltage reading that is higher than the 470, 220 and 100 ohm resistors. Mixing salt into the mud should increase the power output for all the resistors. It does not matter which resistor you measure first.

A broken cathode will affect your MFC power, but don’t try to glue it or sew it. What I would do is to take the hacker board off the fuel cell, take out the cathode and remove the wire, then holding the broken parts together, push the wire into the electrode again so that it penetrates BOTH pieces. Place the cathode back on top of the mud. The mud should be damp to insure good electrical contact with all parts of the electrode. Make sure the broken parts of the electrode are tight together and carefully replace the hacker board so as not to disturb the electrode.

Let the fuel cell rest for half an hour or so then measure the V. When the output has stabilized again let us know by replying to this thread.

Good luck!

Sybee

Hello,

I never took it to radio shack because my multimeter seemed to be working once my mom had helped me.

My first trial lasted five days though my lowest resistors were geting the highest power outputs and that seems to be wrong from what u previously said. But forward the end it started to drop the power output.

I started my second trial two days ago yesterday I measured and I got the highest resistors with the highest readings. I then added salt. I measured today and everything just dropped a lot.

I am growing very frustrated this is o on the 27 I thought I could finish my trials by the 15-20th but everything is going wrong completely.

My hacker board is perfectly fine.

Should I just keep the numbers that I have even though they are completely wrong?

I am following every step exactly with my mom along side me.

Problems and unforeseen results are unfortunately common in science. We redesign experiments, brainstorm with colleagues and try again. Sometimes we figure out why something happened and sometimes not.

If the voltage dropped after you added salt there are a couple of possibilities that are explained on the project's procedure pages. Disruption of the microbial layer next to the anode can reduce their activity as can the introduction of oxygen when you stirred in the salt. Did you add the correct amount of salt for the volume of mud? Too much salt can inhibit bacteria.

I would make sure the mud is still moist and keep doing voltage readings. Your results are not wrong. They are exactly what you found and it is up to you to come up with a logical explanation for them. Sometimes the greatest breakthroughs in science happen through an accident and if a scientist throws out data that doesn't look like what he expected then something important may be missed.

There is a lot of information on the web about microbial fuel cells and you should sit down for a couple hours and do some searching for how you might have gotten the results you got and how to make the system produce more power. Maybe you will find a solution know one else has thought of. At least you will understand the system better and can explain to people what might have happened.

Keep on with your project and let us know what happens. We can't be there with you but we'll try to answer your questions and help you complete the work well.

Good luck!

Sybee