Science Buddies: "Ask an Expert"

In background, it says that biogas is produced from anaerobic bacteria. My question is how will the cow manure+ vegetable peelings produce the biogas in a soda bottle which will probably have oxygen inside?

Excellent question!

Here, it's good to keep in mind that "anaerobic" actually can describe a number of bacteria, all of which have different oxygen tolerances. Of course, some anaerobic bacteria cannot stand oxygen, and will die. Others will tolerate oxygen, but continue to grow anaerobically. Some others will actually switch to aerobic "mode" and start using the oxygen if they detect enough of it!

I'm not sure what species of bacteria are responsible for biogas production, but certainly they must have some level of tolerance if they can produce measurable amounts of biogas. If you're interested in this specifically, you could even add this to your experiment. You could try having biogas bottles with different levels of oxygen and see if that makes a difference. I think that would be a fascinating experiment!

Finally, it's worth noting that since it's a sealed bottle, any oxygen that is "used up" by any aerobic bacteria in the environment will not be replenished from the atmosphere. This probably will have an additional effect (certainly compared to an unsealed bottle), but not that big of one.

Hope that helps!