Science Buddies: "Ask an Expert"

Hello,

I am planning on doing the project "Turn Mud into Energy with a microbial fuell cell- and a Dash of Salt," where you measure the voltage of a microbial fuel cell based on the amount of salt that you add. My science teachers told me that I can't do the project unless I can control the variables, including the amount of bacteria. If I don't control the amount of bacteria from trial to trial, then my data will be skewed. (is this true?) I have researched how to control the amount of bacteria, but have not found anything. Is it even possible to do so? I read that the bacteria forms inside the microbial fuel cell, would there be a way to control the amount that form?

If there is no way to measure to control the amount of bacteria in the fuel cell, will my data be skewed. Do you even need to control the bacteria, because it doesn't look like you do in the Science Buddies project.


Thanks so much!

Hi claram1,

To the best of my knowledge, there is no way to control the exact number of bacteria cells in the microbial fuel cell (there are millions or maybe billions of bacteria, so there's not really any way to count them). I think the best you can do is control the conditions in which the bacteria grow to make sure they are consistent between trials. Step 2 of the procedure describes preparing the topsoil, and the materials list says that you can use topsoil from outside or you can purchase bags of topsoil.

What you do NOT want to do, for example, is take soil from two completely different times/locations outside and use them for different trials (like muddy soil from near a creek for one trial, and dry soil from the middle of a field for another), as that soil could have very different amounts of bacteria and nutrients to begin with, and that would skew your data. My guess is that buying a bag of topsoil would be the most consistent approach.

However, the point of the experiment is to see how adding salt affects the power output. So, even if the exact # of bacteria is not the same from trial to trial, you should still be able to see the trends that result from adding salt (does power output increase, decrease, or stay the same?).

Thanks !