Science Buddies: "Ask an Expert"

Hello,

After doing the "From Trash To Gas: Biomass Energy" science project, my daughter noticed the following:

The mashed banana mixed with cow manure, which produced the most biogas, peaked in its biogas production around days 12-13. (My daughter ran the experiment for 14 days)

The potato and carrot peelings mixed with cow manure produced less biogas than the banana with their highest amount being produced between days 3-5.

My daughter is wondering why the biogas produced by the potato-carrot peelings & cow manure mixture peaked much earlier than the biogas produced by the banana & cow manure mixture.

She researched and found that the amount sugar in bananas is higher than that in potato and carrot peelings. She read that sugar is important in the decomposition process. Furthermore, she read that there is more fiber in potato and carrot peelings than there is in the flesh of bananas and that fiber is difficult to digest/decompose.

She would therefore like to know if she is on the right track in thinking that it is the amounts of sugar and fiber in the banana flesh and potato-carrot peelings that has affected the peak time of biogas production in the banana/cow manure mixture and potato-carrot peelings/cow manure mixture.

Could you please advise us on this and let us know of any resources that my daughter should research to answer this question?

Thank you!


[Administrator note: project can be viewed here: https://www.sciencebuddies.org/science- ... ass-energy]

Dear Biogas18,

I think that she is on the right track. Ripe bananas contain sucrose, fructose and glucose. Also, carrots contain sugars, such as sucrose, glucose, and fructose and potatoes contain fructose, sucrose, and glucose. When these are broken down into simple sugars, they convert to energy. When you look at the amount of sugar in bananas, carrots, and potatoes, bananas (12 g per 100 g) have more sugar than carrots (4.7 g per 100 g) and potatoes (0.8 g per 100 g). This shows that bananas are more capable of converting their energy, which is essential in the production of biogas. Moreover, I found out that fiber is not broken down during digestion, therefore our bodies rely on carbohydrates to obtain energy.

In addition, since biomass contains stored energy from the sun, it is also important to compare the amount of calories in each one. This means that if a biomass have more energy, it is more capable of creating more energy with cow manure. Bananas have 8.9 calories per 10 g, carrots have 4.1 calories per 10 g, and potato skin have 20.3 calories per 10 g. When 4.1 calories and 20.3 calories are added together, you will get 24.4 calories. 20.4 calories outweighs 8.9 calories of bananas.

These are the resources that I used:
https://www.umass.edu/nibble/infofile/fiber.html
http://www.ei.lehigh.edu/eli/energy/res ... iomass.pdf
Google Calorie/Sugar Calculator

I hope this is helpful. If you have any questions, please let me know.

RicaC