Science Buddies: "Ask an Expert"

Hi, my project is similar to the "From Trash to Gas" biomass project on here, where I fill three 2 liter bottles with cow manure, three with cow manure and vegetable peelings, three with cow manure and corn stalks, and three with cow manure and salt. All of them have water added to them. I had taped balloons to the neck of the bottle, and expected them to blow up after a week or so. At first, two of the vegetable peeling bottles blew up a little, but immediately deflated after two or three days. I've waited three weeks now, and they are all completely deflated now. Can someone help me? Thank you!

Hi EJ63 ,

Welcome to Science Buddies! I think you are doing this very excellent project from the Science Buddies website:

https://www.sciencebuddies.org/science- ... p027.shtml

It sounds like you observed some gas production about the right time, but not as much as would be expected. The production of methane is done by obligately anaerobic bacteria growing under anaerobic conditions. So you may not have had the right bacteria or growth conditions in you samples. Here are some questions that may explain your results:

Did you use very fresh manure? The methane-producing bacteria are sensitive to oxygen and will die if exposed to oxygen, so it's important to use a fresh sample, straight from the cow.

Did you use cow manure? Non ruminant animals may not have high concentrations of methane producing bacteria.

Did you agitate or shake the samples any time? This would add oxygen to the sample; it is important to leave the bottles stationary during this experiment.

What temperature was it? The methane bacteria have an optimum temperature that is the normal temperature of cows. So if it was too cold, they might not have grown very well.

What was in your samples? Could they have contained anything that would have inhibited bacterial growth?

Please note that you have a complete project and you should write up the results for your display board. Your conclusion and discussion section should include a complete discussion of what may have happened and what you would do differently next time, but your project is scientifically valid. If you can, you can set up the samples again, but you may not have time to obtain new results. But a quick experiment might help verify the source of the problem that you experienced.

Please post again in this topic if you have questions.

Donna Hardy