Science Buddies: "Ask an Expert"

Hi Anna,

I see you started a new thread on this topic. I'm sorry I didn't see your earlier reply. I thought I had responded to your last questions, but I can't find my last answer. I'll answer here so we can continue on this topic.

If you pull the balloon over the top of the soda bottle, it should be secure enough to fill with any gas that the bacteria are producing from fermenting the sample. If your balloons are not expanding, check to make sure they are securely attached to the top of the bottle. If that is not the problem, then your temperature is probably too low. What temperature are you using? If it's below 24 degrees Centigrade/75 degrees Fahrenheit, try moving at least one bottle to a warmer place for a day to see if that will make any difference. Be sure to get permission if you need to bring a bottle inside, as the sample will be very aromatic if the balloon expands so much that it comes off the bottle.

When is your project due?

Donna Hardy

I am wondering how long to leave our 2-L bottles at about 20-22 C with manure and veggie peelings? They have been at this temp for about 1.5 weeks. When should we expect results (the balloons to fill).

Hi,

I would have expected some results by now. Your temperature is high enough for some microbial activity. Please check the following:

1. Are the balloons airtight on the top of the bottle? Do you see any difference at all in the volume of the balloon?
2. Can you see any signs that the vegetable peels are being fermented? If the bacteria are growing, you should see something visible change in the appearance of the vegetables.
3. Did you use fresh manure? What quantity of manure and vegetables did you use?
4. Are your samples dry or wet? Describe the appearance.
5. Do you have some baking powder and vinegar, or some yeast, sugar and water, that you can use as a "positive control," to check to make sure your bottles and balloons will work as expected?

When is your project due?

Donna Hardy

Yes the bacteria has worked on the veggie peelings. It has become a cloudy mixture. We used 10 g of fresh manure (cow, horse, and chicken separtly) mixed with 5 gram potato peelings. Filled the bottle with d-water, placed latex balloon on top (secured with tape). We did have a control of just the veggie peelings and they still look the same. We have 8 total bottles and we really do not see any differences in the balloons. The science fair is coming up soon (the 25th) so we are getting worried. This is the second trial we have tried, b/c the first run we did not use the veggies and started back over from scratch.

Hi,

It sounds like you set up the biogas experiment according to directions, and it sounds like bacteria are growing because the solution has turned cloudy, however, the bacteria you are growing are not producing gas. The bacteria that produce biogas are anaerobes, and the cow manure contained lots of these organisms, but conditions may not be anaerobic in your bottles. I would recommend leaving them to see if conditions become more anaerobic and allow the biogas organisms to grow. The methanogens are extremely obligate anaerobes and will not grow if any oxygen is present.

The production of biogas depends on the growth of several different types of bacteria. The methanogenic bacteria you are trying to grow use acetic acid , hydrogen, and carbon dioxide produced by other organisms to produce the methane. I’m sure conditions were optimum for methane gas when the manure was very fresh, but perhaps the balance of organisms is not right in the bottles for some reason and the raw materials needed by the methanogenic bacteria are not being produced.

http://www.oregon.gov/ENERGY/RENEW/Biomass/biogas.shtml

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

When humans, plants, and animals metabolize energy sources, they use oxygen to accept extra electrons that are produced from breakdown of sugars. When anaerobic bacteria metabolize energy sources, they need an electron acceptor, but cannot use oxygen. They can use nitrate, iron, and other metals to accept electrons. I would have expected that electron acceptors would be available in the materials you added to the bottles. Nitrates are common components of many vegetables, so I’m sure this is available in your samples.

Here are two suggestions that you can try, if you have an extra bottle of manure/veggie water available. You can add a teaspoon of vinegar (acetate) to a bottle in case the bacteria are not breaking down the vegetables peels quickly enough to see if that will make a difference. Also, you could try increasing the temperature of your samples if that is possible. Your temperature is high enough to support bacterial growth, but these organisms would grow faster if you could increase the temperature up to 37 degrees Centigrade.

Since the science fair is only a few days away, you should write up your results as they are right now. You do have a successful project and lots to talk about; you just don’t have the results you expected. Be sure to include background information and in the conclusion section, you will need to explain why no gas formed (oxygen may have killed the anaerobes, etc). You should include some ideas of what you would do differently if you were to do this project again. If you don’t see any gas production at all, then you can conclude that your project is a recycling experiment.

I hope this helps.

Donna Hardy

Thank you so much for taking the time to help with this issue. Very good advice. I would like to ask a couple of other questions though: 1) should we be shaking the bottles and 2) we ran this experiment in duplicate so do you recommend using one of the set of bottles to add the vinegar to? I am going to try to put a heat lamp on the bottles to try to get the temp up somewhat, so maybe that will get something started. I guess if we have been moving the bottles that would be adding oxygen, right?

We will report our data as is, but leave the experiment set up. This is the local science fair and I guess there is a hope of making it to the district. That science fair is not until April 30th, so by that time.....gas may be produced.

Hi,

If you shake the bottles, then you would be adding oxygen, which would inhibit the methanogens, so leave the bottles stationary. Hopefully the facultative anaerobes will grow and use up all of the oxygen so the anaerobes that produce methane can start growing. If you have been shaking the bottles, then that would be a good reason why you haven't seen any gas formation yet, and you should include it in your discussion section.

The heat lamps are a good idea, but make sure the temperature does not exceed 37 degrees Centigrade to avoid cooking the bacteria. If you can increase the temperature from 20 to 30 degrees Centigrade, the growth rate of the bacteria will double.

And your plan is a good one. Leave the bottles incubating and hopefully some gas will start forming before next week's science fair, or at least before the district fair.

Let me know what happens.

Donna Hardy

Just wanted to let you know that we have balloons that are filling with gas:) Right now, the cow manure is producing the most biogas, but the chicken is also producing. Thanks for your help!!!

Hi,

Yea!!!! This is really good news. And just in time too. I'm so happy you have some results. Are you going to measure the circumference of the ballooons so you can calculate the volume of gas produced?

Did you use the heat lamps? Did you switch from shaking to stationary? What was the difference in your experiment that allowed the growth to occur?

Donna Hardy

This is a 4th grade project, so I think we are going to stick with measuring the circumference of the balloon with a string and then laying it on a ruler to get cm. I am not sure that the volume calculation would be appropriate for a 4th grader????

We stopped shaking the bottles and we cranked up the heat with a heat lamp to about 25-28 degrees C. It seemed like overnight, the bacteria agreed with this and starting producing gas. We also noticed that the smell intensified! We are planning on taking data for 5 days (am and pm) and reporting our results. We are on day 3 right now. The control groups (no manure) haven't produced any gas, so we are happy about that. This is really pushing it to the last minute, and we usually don't like to be in that position but that is just the way it rolls.

We found out that the science fair is awarding a new category ("go green" efforts). So our implications will be directed toward this:)

Hi,

Yes, you are right; calculating the volume of a sphere is probably too advanced for a 4th grader. Just in case you want to try, the formula is volume (4)(3.14)(radius cubed) /divided by 3. I think circumference will be perfect for purposes of this project. Do you think your 4th grader could make a graph of the results? A bar graph would work well for the data.

Thanks for telling me what helped your results. This will help me in giving advice if anyone ever does this project again.

This is the perfect project for the green category. And, it's so nice to have some data.

Donna

Thanks again for you help. I think the biggest factor was that we quit moving the bottles around each evening. Also, if I were to do this again, I would keep the temp above 25 deg C. We might also use a smaller plastic bottle (such as a .5L water bottle) and a smaller latex balloon. We did not see any huge balloon "blow-up" results b/c our balloons were rather large. We are having to manipulate them to where the air is all at the tip and then measure the circumference. I know it is not going to be an exact measurement, but we are trying to at least be consistent b/w the trials.

We did get good results from the cow and chicken, but I was surprised that the horse manure did not produce much biogas. Horse manure is often used in compost piles for the heat that is produces, so I was expecting it to do really well. Other than the lack of anaerobes in the horse gut (but chickens should also have this issue), any suggestions as to why the horse did not produce?

Hi,

Thanks for the details on the results. I will definitely remember this for the next project.

Interesting observation. I don’t know exactly why the horse manure produced less gas, but I can think of some possibilities. Here is some background information first:

The microorganisms that are associated with biogas formation are present in the intestinal tracts of animals that harbor microorganisms that can break down cellulose. The digestive tracts of cows, horses and chickens are different and the difference could result in different types of microorganisms. Cows have 4 stomachs and a very efficient digestive system for fermenting cellulose into usable sugars. Horses only have one stomach and so may not be as efficient as cows in digesting cellulose. Chickens have a large ceaca that stores bacteria that can break down cellulose.


http://www.vivo.colostate.edu/hbooks/pa ... orses.html

http://www.ca.uky.edu/smallflocks/Facts ... estive.pdf

http://animalscience.tamu.edu/images/pd ... system.pdf

The possible reasons for less gas in the horse manure include:

1. The horse manure may have contained a lower number of methanogenic bacteria because the horse does not digest cellulose as efficiently as cows and chickens. When the samples were collected, do you remember if the horse samples looked like they contained more undigested plant material compared to the chicken and cow manure?
2. Maybe the horse’s normal flora was out of balance because it was on antibiotics or was ill.
3. Maybe the agitation the bacteria were exposed to during the early part of the experiment exposed the horse’s bacteria to lethal amounts of oxygen and they did not survive until you left the bottles stationary. Many of the bacteria that produce methane are obligate anaerobes and will die if exposed to oxygen.

Can your fourth grader think of an experiment that could be done for next year’s science fair project that would prove why the horse manure produced less gas compared to chicken or cow manure? I have done science projects with kids over the summer, and this one would be ideal to do because it will work better with the warmer temperature. You can do the project, record the results, and then about a week before next year’s science fair get out the results and write up the board. There are lots of good projects that can be done in the summertime such as insect projects, which cannot be done during the winter.

I hope this helps.


Donna Hardy

Just wanted to let you know that the project won its division. We are now going on to the regional science fair....thanks again for your help. Everyone really loved the idea and the display.

Hi,

Congratulations! I'm so happy that your son's project won. He deserves credit for doing an excellent project.

Thanks for letting us know about your success in the science fair.

Donna Hardy

Hello,
I've followed this thread with much interest. I'm interested in knowing a few more details about this experiment from someone who's actually done it (or from an expert who could hypothesize the answers to my questions). I'm a writer of children's books and my main character is doing this experiment. Unfortunately, I don't have the space in my house and outside it's too cold to conduct the experiment myself. I need a few more details to make sure I'm presenting it accurately in the story.

Mainly, I'm wondering if 5 grams of manure (for the manure+peelings and manure+bananas bottles) and 10 g of manure for the manure-only bottles actually results in much inflation of the balloons. I got these measurements from the science buddies experiment "Trash to Gas: Biomass Energy." (I'm assuming a temp of about 35 degrees Centigrade).

Also, how long does it take to start seeing some inflation and how big would the balloons get? I found the original experiment report that the science buddies "Trash to Gas: Biomass Energy" experiment was based on and at the height of this student's balloon growth, some of the balloons were measuring a diameter of 34 cm. If I'm calculating correctly, that's a circumference of 106.8 cm, right? Does that sound possible? Also, science buddies recommends measuring the balloons in mm, but this student did hers in cm. So I'm wondering which is better. There's a big difference between mm and cm and if measuring in mm, it makes me think the balloon growth wouldn't actually be as big as I was envisioning (and portraying) it.

Another big issue I want to be accurate on -- do the bottles smell? I realize they are sealed by the balloons, but would the methane smell leak through the balloons, or would you only smell it if the balloons slip off the bottles? My character is doing the experiment inside his heated basement (with a window open for ventilation). Would it smell in the room?

Thanks for any help you can give!

Hi,

What a great idea for a children’s book! Is your character doing a science fair project, or just doing the project for fun? I am very impressed that you are taking the time to verify the details of the experiment. It will make your story much more credible.

I have not done this experiment, but I can explain the science behind it to you. Here are answers to your questions:

5 grams of vegetable matter and 10 grams of cow manure is enough biomass to fill of balloon with biogas if the bacterial fermentation proceeds as expected. In this experiment, bacteria from the cow manure break down the cellulose in the vegetable sample to glucose and then to methane gas; each glucose molecule can be converted to 3 molecules of methane plus 3 molecules of carbon dioxide. Assuming that the 5 gram sample contains 80% cellulose and other fermentable sugars, there would potentially be 0.02 moles of glucose that would be converted to 0.06 moles of methane and 0.06 moles of carbon dioxide. The 0.12 M of gas would occupy 2.7 liters at room temperature (about 22 degrees Centigrade) or 2.8 liters at 35 degrees Centigrade, which is enough gas to fill a balloon. If your character is the type that wants to do all the calculations, let me know and I’ll include more details, but I think the chemical reactions and standard gas laws are probably too advanced for most elementary readers. However, if your character is a genius, or if this is for older children, maybe you will want to include some details.

It takes a few days before gas starts to form, and it does depend on having the right type of bacteria and the temperature. The first part of the reaction involves the breakdown of cellulose to glucose and the growth of facultative microorganisms to remove all of the oxygen from the sample. Once the cellulose has been degraded and the oxygen is gone, then the obligate anaerobic methane-producing bacteria can start to grow and produce gas. The student who did this project was mixing the samples every day, inadvertently adding a little oxygen in the process, so the methane producing microbes did not start growing until the samples were left stationary. I would say it would take at least 5-7 days before gas would start to form.

I don’t know what your scientific background is, but here are a couple of websites that include helpful background information. The first one describes how bacteria convert cellulose to methane, and the second describes the ideal gas laws that can be used to determine the quantity of gas produced.
http://www.ncbi.nlm.nih.gov/pmc/article ... 8-0259.pdf

http://en.wikipedia.org/wiki/Standard_c ... d_pressure

When doing science experiments, we always encourage students to use metric measurements. The diameter of a balloon can be measured in millimeters (1/1000th of a meter) or in centimeters (1/100th of a meter), so a measurement would be, for example 183 mm or 18.3 cm, and either value would be perfectly acceptable to a science fair judge. To measure the circumference of a balloon, you can determine the length of string necessary to reach around the largest diameter and then measure the length of string using a ruler.

Anaerobic bacteria degrade biological materials and produce small volatile organic compounds that have characteristic odors that most people would consider unpleasant. Sewage plants, animal manure, and septic tanks are all examples of anaerobic fermentation processes that are associated with certain aromas. This experiment uses bacteria from cow manure and provides a source of food and ideal conditions for anaerobic growth. It’s interesting that the methane and carbon dioxide would not have an odor, but other metabolic end-products would definitely be produced. I think that a basement with an open window would be a good location for your character to do this experiment, since it is somewhat isolated from the main part of the house. Your character has chosen a project that involves collecting and handling fresh animal manure, so I’m sure he will not be bothered at all by the slight smell.

The ideal temperature for this experiment is about 35 degrees Centigrade, but a basement with an open window is going to be much cooler, especially in the winter. How is your character going to keep the samples warm enough to provide an ideal temperature for the bacteria to grow?

The gas produced in the balloon is a small quantity, but is potentially flammable, so your character should be careful not to expose the balloon to an open flame, like a burning candle. Otherwise the project will be destroyed in a flash. Please also note that the project guide specifies washing hands with soap and water after setting up the experiment, and this is an important safety precaution in this experiment.

One important detail for a successful project is that the source of bacteria must be from a ruminant animal like a cow that has the ability to digest cellulose and the sample must be really fresh to ensure that the microorganisms are viable.

Please let us know if you have any other questions. I'm sure that your book will inspire children to do their own science project, and maybe consider a future career in science.


Donna Hardy

p.s. If you are thinking ahead for your next book, or considering a series, check out the Science Buddies project on slime molds.

Thank you, Donna, for your very helpful reply.

The character in my book, Brendan, is partnered with another student and they are entering a science competition, something their 6th-grade science teacher has them doing. And while Brendan is very bright, I don't think all the details of amounts of gas, etc, will be necessary -- if for no other reason than it's way beyond my comprehension! (I don't have a science background -- just a natural curiosity about lots of things!) But it's very good to have a scientific explanation to support that the balloons WOULD fill with these amounts of biomass, given the right conditions.

They are keeping the room at the proper temperature with a space heater -- I realize it would have to be very warm (and would undoubtedly impact Brendan's family's electricity bill!), but he's gotten his parents' permission.

I'm still not totally sure about whether the room would smell, however -- like if someone walked in, not knowing the experiment was in the room, would the smell be one of the first things they noticed? Could the smell escape through the latex of the balloons? Or will it only smell if the balloons are removed?

Eventually, there is an accident in which the bottles get toppled and one bottle's contents end up on the floor -- that would smell obviously -- but what about when the bottles are just sitting there, upright, with balloons over the mouths? Currently, I have it smelling when the bottles are just sitting there in this warm room (ie, before the accident), but I'm not a hundred percent certain it would. Any way to verify this?

Thank you, again, Donna. And I'll be sure to check out the experiment on slime molds -- sounds intriguing! In case you're interested, the book will be titled: "Brendan Buckley's Sixth-Grade Experiment." (The main character is entering middle school -- so "experiment" refers to more than just the literal experiment.) It's a sequel to the book, "Brendan Buckley's Universe and Everything in It," which came out in 2007 and has done well enough that a sequel seemed like a good idea. Hopefully Brendan will indeed encourage many kids to pursue science!

Sundee

Hi Sundee,

Hi Sundee,

Thanks for your reply, and for the additional information about your new book. It sounds like a wonderful idea for a book..

I was hoping the student who did this project last year would post and let you know about the magnitude of the odor when the balloon was in place on the bottle. However, anaerobes create a very strong smell, and I think the odor would be detectable even with the balloon in place, kind of like when you open the refrigerator and there’s something that is spoiling inside. Balloons do have a porosity for small molecules so I think they would slowly diffuse into the room air. However, the only way to absolutely verify this would be to set up a balloon with something volatile and put it a room and see if you could smell it. I would try something volatile like perfume, if possible. Other wise, assume a slight background odor with the balloon in place, and a very strong odor when it spills.

Good luck with your project. Let me know if you need any additional information.

Donna Hardy

Hi Sundee,

Hi Sundee,

Thanks for your reply, and for the additional information about your new book. It sounds like a wonderful idea for a book..

I was hoping the student who did this project last year would post and let you know about the magnitude of the odor when the balloon was in place on the bottle. However, anaerobes create a very strong smell, and I think the odor would be detectable even with the balloon in place, kind of like when you open the refrigerator and there’s something that is spoiling inside. Balloons do have a porosity for small molecules so I think they would slowly diffuse into the room air. However, the only way to absolutely verify this would be to set up a balloon with something volatile and put it a room and see if you could smell it. I would try something volatile like perfume, if possible. Other wise, assume a slight background odor with the balloon in place, and a very strong odor when it spills.

Good luck with your project. Let me know if you need any additional information.

Donna Hardy

Thank you, Donna. Much appreciated! I would very much like to acknowledge you in my acknowledgments section -- are you Dr. Donna Hardy?

i have read these posts with MUCH intrest! i am hoping to do this expiriment next but i need a bit more info!do you think someone could help me with that?(:
Thanks!(:
ASHLEY(:

Hi Sundee,

Thanks for asking, and thank-you in advance for the acknowledgement for Science Buddies. I am not a Dr, so no title is needed. I am looking forward to reading your new book, so let us know when it is published.

Donna Hardy

Hi Ashley,

This is an exciting project that you could develop into a unique prize-winning project. However, it seems like it the past the deadline for your project. If you have at least 2-3 weeks before deadline, then read the following project guideline and do as much background reading as possible. It would also be helpful to review the guidelines for doing a project from the Science Buddies website:

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

https://www.sciencebuddies.org/science- ... l?From=Tab

If you are going to proceed, then please start another thread so the science buddies volunteers can help you with your own project. If you don’t have time to complete this project, it would be an excellent one to do over the summer for next year’s science fair. It works better in warmer weather and it’s a project that is easier to do outside.

Donna Hardy