Science Buddies: "Ask an Expert"

im having an expirement about the production of biogas, and im planning to make my own generator for it. something like this: http://webarchive.nationalarchives.gov. ... e23327.pdf .. but i have some questions concerning this like:

1. how do i know/test that the gas produced is methane?
2. how can i measure the amount of biogas from the diffrent biomass(im having 5 diffrent kinds)
3. and will i be able to collect the biomass using this simple generator? if so, how?

i hope you can help me with this one. =D

Hi,

Welcome to Science Buddies!

This is a really great project and there is also a similar project on the Science Buddies website that includes helpful background information:

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

1. Methane has a lower density compared to air. In your project, the gas is collected in a balloon. If the balloon floats in air, then you can confirm that it’s methane.

Here is a table that includes the density of gases:

http://www.engineeringtoolbox.com/gas-d ... d_158.html

What other gases would you expect to be produced by microorganisms?

2 & 3. You will be collecting the biogas in a balloon. If you choose a round balloon, you can measure the circumference of the balloon to calculate the volume of gas produced and compare the volume of the 5 balloons.

What will you use for a control?

Have you had any chemistry in your science classes yet? If you measure the temperature in degrees Centigrade and record the barometric pressure, you should be able to calculate the moles of gas produced. Here is information on the ideal gas law.

http://en.wikipedia.org/wiki/Ideal_gas_law

There’s a lot of chemistry in this project so let me know if you need additional explanation.


Donna Hardy

thanks for the reply. =D
but i have some additional questions like in number 1, i mean is it enough for me to say that its methane because it floats? i mean there are alot of gasses that can make the baloon float(helium,hydrogen(which can be produce by bacteria)) and sumthing. i would really apreciate it if you can explain more on that part.

and for number 3, when/how will i measure the temp?(after experiment or during). and how & when will i be able to get the pressure using the barometric pressure?? and for the ideal gas law,is the "n" in the equation PV=nRT gives me the amount of biogas present?? sorry for the many questions. i didnt have any chem classes yet so im not that good at this.

Hi,

Anaerobic bacteria will generate either methane or hydrogen gas, so I would not expect any helium to be present in the samples. If oxygen is available, bacteria will be able to ferment any sugars in the sample to form carbon dioxide, which is more dense than air and would cause the balloons to sink rapidly.

Methane and hydrogen gas (and other gases) can be identified by an analytical method called gas chromatography. This requires special equipment and access to a laboratory. This type of gas analysis is commonly done by gastroenterologists in clinical laboratories. Here is a paper that describes this type of study:

http://www.wjgnet.com/1007-9327/12/3088.asp

Do you have access to a laboratory that could analyze a few samples for you? If not, then you can describe this technique and explain what you would do if you had access to a laboratory.

If you are interested, I can explain more about the ideal gas law after you have obtained some results and have measurements for your balloons. Otherwise, since you haven't had chemistry, this type of analysis could be considered outside the scope of your project. However, it would be good to include some general information on this topic in your discussion section so the judges will know that you at least are aware of the subject.

This project requires really fresh manure. Do you have a source that you can collect the manure and set up your experiment quickly with a minimum exposure to oxygen? Also, anaerobic bacteria produce very aromatic volatile compounds when they grow, so it's best to set up this experiment outside of the house. And, temperature is important. The bacteria will grow faster at a higher temperature, so do try to set up this experiment when the weather is as warm as possible. You should have a thermometer and measure the temperature.

You have good questions. Let me know if you have any other questions.

Donna Hardy