Science Buddies: "Ask an Expert"

My son has selected the "trash to gas" experiment for his science project. He has conducted the experiment using the various medium (cow manure only, vegi peels + cow manure, and bananas + cow manure) with poor results. Only two of the bottles resulted in gas being produced (bananas + cow manure).

Even though the experiment was not completely successful, I still believe that it was useful in understanding biomass and how the process works. Since he does not have time to redo the experiment can you please provide some information on expected results of the experiment? If performed properly which medium would be expected to produce the most gas or produce gas the fastest and why? This will help my sone explain the results even though his actual experiment outcome was not conclusive.

Thank you

I would think that the one with just cow manure would produce the least biomass. Fruit peels and vegetable peels might have around the same amount of biomass, but I'm not really sure.

Here is a part of an abstract of an experiment that I found: "The biochemical methane potential of 54 fruits and vegetable wastes samples and eight standard biomass samples were determined in order to compare extents and rates of their conversion to methane. All the samples were obtained fresh, grown in nutrient enriched environment and belonged to mature age group. The ultimate methane yields (B0) and kinetics of fruit wastes ranged from 0.18 to 0.732 l g−1 VS added and 0.016 to 0.122 d−1, respectively, and that of vegetable wastes ranged from 0.19 to 0.4 l g−1 VS added and 0.053 to 0.125 d−1, respectively."

I don't really know much about biomass, but you can probably look up biomass levels for banana peels and vegetable peels then predict an expected result. Here are some key words: Fruit wastes, Vegetable wastes, Methane yield, Methane production rate, Biochemical methane potential, Biomass

Thank you for your input. This will help my son. One additional question regarding expected results. Why would the specimens with the manure plus other biomass (bananas or vegetable peels) be expected to produce more biogas than just the cow manure alone? Again, this information will assist my son in his conclusions.

Hello there,

I think the answer to your question is actually quite simple - its because there is more biomass to get energy from...all organic matter are great sources of energy and vegetable peels and bananas definitely count as organic matter so together they will produce more biogas than just cow manure alone...

Hope that helps!
Prasad

My son did this experiment and we really do not have anything to work with on our results. It seems that each of the balloons (except for 2 of the bottles) the balloons actually tore. Not sure if the balloon tore because of the amount of Cow Manure I used. Do you think the Biogas caused the tear down of hte balloon?