Science Buddies: "Ask an Expert"

I am one the fourth day of my experiment and the balloons on the bottles are actually being sucked in. It is the middle of winter and i have read that the bottles should be in warm temp. i don't know what to do.

Hi curmau19,

Are the balloons in a colder place then where you attached them to the bottles? If so, then the decrease in temperature will lead to a decrease in gas volume. That might explain the shrinking balloons. How cold is it where the balloons are? If it is below freezing, it's possible the organisms in the biomass may be dead. How fresh was the cow manure you used? Did the balloons ever inflate at all? Post back with answers to these questions, and I'll help you troubleshoot. The more details you can provide the better!

About forty five degrees with a heat lamp on them
very fresh manure
no the balloons never inflated

Hi curmau19,

Thanks for the additional information - it is very helpful. One thing to keep in mind is that the rate of bacterial growth depends strongly on temperature. That's why food takes longer to spoil in the fridge than on your counter. The bacteria in your fridge reproduce much more slowly because of the lower temperature. Since the cow manure was fresh, it should have the bacteria, etc. to make the project work. My best guess is that the low temperatures are slowing down the production rate of gas. You could either keep waiting for a while or else bring the bottles into a warmer area. If you bring them into a warmer area and the balloons inflate after a few days, then the problem was the cold temperatures. If you bring the bottles into a warmer place, but there still isn't gas in the balloons after a few days, then the problem is probably something else.

The veggie peelings mixture is starting to produce a little gas.

Today was about 10 degrees colder and some of the balloons that did produce shrank a little.

These results sound consistent with Terik's response. I think you have a very interesting result there to discuss for your project. Perhaps you should do a few control experiments with bottles that contain no gas-producing materials to see if they shrink and grow along with your test samples.