Does water affect degradation of organic substances?

[donnahardy2]

Hi Trexzert,

Thanks for letting me know. It's hard to do anything without a computer these days. Just do as much as you can and let me know about your progress, and if you need more information.


Donna Hardy

[trexzert]

When I put the banana peels in the soil, I should wrap it all together in a fabric that has tiny holes to let bacteria in while keeping out the soil. So then after 1 week, I can just take the fabric along with the peels out and no soil will be in the banana. Then, I could measure the combined grams of the banana. At the last week of the experiment, should I test the volume of the banana peels in each box? I'd use a graduated cylinder. The water would ruin the banana peel but since I'll do this on the last week, it doesn't really matter.

[donnahardy2]

Hi Trexzert,

Yes, you can wrap the banana peel in a bag with tiny holes. When you bury the banana peel in the soil, you can press down gently to make sure the soil is as close as possible to the banana peel to allow the bacteria easy access and to make sure the moisture in the soil will equilibrate with the banana peel. You don't want the banana peel to be in a pocket of air. You could tie a string to the porous bag that goes up to the surface, so it will be easy to drag the banana peel bag out of the soil when you are ready to weigh it. Do make sure that your technique of burying the banana peels is identical for all samples, as this is one of your controlled parameters (conditions of the experiment)

It sounds like you are ready to get started on your experiment! Let me know about your progress.

Donna Hardy

[trexzert]

I'm so close to starting. It's just the porous bags that I need. I have all the banana peels. Can I find porous bags in many supermarkets?

[trexzert]

Oh I found out the teachers extended the science fair project due date to Feb 19 and that we can't start the experiment until Dec 16.

[donnahardy2]

Hi Trexzert,

That's good news that you have until February 19. This project will benefit from the extra time. You can spread your data points out over a longer period of time, and plan to stop the experiment on about February 12. Why can't you start until December 16th? If you have all of the banana peels collected, it would be good to get them buried to start the composting process.

I believe there is a porous bag available in the baggie section of the supermarket. You could also get netting from a fabric store and tie the peels up in a square piece of the netting. Any type of cotton or nylon cloth would probably work also. Bacteria are only a micron or so in size, so the pores don't have to be very big. If water can drip through the fabric, then the pores are big enough, even if you can't see them. I have talked to many soil scientists in the past and they all say that the best and least expensive porous bag to use for this type of experiment is fabric that pantyhose are made from.


Donna Hardy

[trexzert]

I almost finished my new procedure for the experiment. I have to hand it in in 3 more days.

[donnahardy2]

Hi Trexzert,

Do you have time to post your procedure before you turn it in? I would be very interested in seeing it.

Donna Hardy

[trexzert]

Here is the copy but actually, I could change it if there are any errors.

Question: Does moisture affect the degradation speed of banana peels? Will having more moisture affect it’s degradation speed?

Hypothesis: Higher moisture content in the soil will promote faster degradation rates.

Materials:
-5 plastic container of equal size. Should be able to fit in 700g+.
-25 banana peels.
-3000 g of soil.
-an electronic scale or balance that can measure to the nearest hundredths.
-Oven with baking sheet.
-5 porous bags that can fit 5 banana peels
-container that has measurements in mL
-20 plastic bags

Procedure:

1. Put 3000g of soil in the oven and set the heat to 200 degrees for 20 minutes. Let it cool.

2. Place 5 banana peels in a porous bag and seal. Then place it in one container. Do the same with the other bags and peels. You should have 5 containers that holds 5 banana peels each in a porous bag.

3. Place in enough soil in each container until it almost fills up to the top.

4. Label your plastic containers from 1-5. Now, get out the container that has measurements in mL and fill in water equal to 50% of the amount of substances that is held in the plastic container. (E.g. If your using a 700g plastic container, then 50% of 700 is 350. So, you would fill in that container with 350ml of water.) For the second container, fill in water equal to 60% of the substances held in the plastic container. For the third, fill in water that equals to 70% of the substances held in the plastic container. 4th one, fill in 80%. 5th one, fill in 90%.

5. You can either close the lid and poke holes through or don’t leave the lid on. Put the 5 plastic containers in a safe spot. (Not outside).

6. Once a week, take out the banana peels in the porous bag and weight it. To make sure no soil is loss, wrap the container with a plastic bag when your taking out the peels. Gently shook off lose dirt and then measure the weight in grams. Put the peels in the porous bag back into the container and any soil in the plastic bag. Do the same with the other 4 containers, but use a different plastic bag.

7. After 4 weeks, compile the information and give a conclusion.

8. Optional but recommended. Redo this experiment with other organic substance. See if this applies to them too.

[trexzert]

My teacher says that I need an appropriate sample size. e.g. 5 banana peels in 50% moisture is only 1 sample size for 50%. I need to have more than 1. This applies to 60%, 70%, 80%, and 90% too. I might need to use less banana peels so that I have enough for the other experiment.

Change:

Actually, due to the fact that I need a experimental control, I have to have a container with no moisture at all.

So the containers with moisture in soil will be 0%, 40%, and 80%.

[trexzert]

I got a good idea. Instead of doing 5 containers with 50, 60, 70, 80, and 90%, I'll just use 3 containers with soil that contain 30% 50% 70% moisture in soil. Because I need a sample size, I'll use another 3 containers and do the same thing. The soil will also be filled with 30%, 50 % and 70% moisture.

[donnahardy2]

Hi Trexzert,

Thanks for posting your procedure again. I do have a couple of comments, and I do agree with your teacher. Here's what I would suggest.

Your control should be a banana peel that you don't bury. You will assume that all of the fresh banana peels contain the same amount of moisture, so you will measure the dry weight of the banana peel (or better, two separate banana peels). You measure the dry weight of the banana by measuring the weight of the fresh banana peel, drying it overnight at 200 degrees F in the oven, the then measuring the weight again. The dry weight of the banana peel is the first point in the graph of your results. Then you bury 5 banana peels in each container in separate porous bags. You will periodically remove one bag containing one banana peel from each box, and measure the moisture content. This will give you a single banana peel with 5 different measurement times over the course of your experiment. Your teacher is correct; if you put all 5 banana peels together, it would be just one sample. Since you have an accurate balance to use, your results should be significant using just one banana peel per data point.

Your experimental design assumes that there will be a decrease in the dry weight of the banana peels over time as they are degraded into individual biomolecules by microorganisms. Your independent variable is the percent moisture in the soil; your dependent variable will be the dry weight of the banana peel that has not been degraded by microorganisms. Can you draw a graph with and X and Y axis, and imagine what your results will look like on the graph?

If you sterilize the soil for all of the samples, you will only have the microorganisms from the banana peels available to start the decomposition process. If you start with a fairly dry soil sample and measure the moisture content of part of the total soil sample, you will have the percent moisture of that sample. You can then add more water to the soil to make samples with higher percentages of water. The unsterilized soil will potentially add hundreds of different microorganisms that could grow on the banana peel, and could speed up the decomposition process. Since this is a science project with a limited time span, it might be to your advantage to not use sterilized soil. You can go either way here (sterilized or unsterilized), as long as all of the samples are the same (controlled conditions), but the decomposition process will probably go faster using unsterilized soil.

One more comment. Your procedure for preparing the soil samples needs to be defined precisely. If you have 1000 grams of (dry) soil in each container, you should add 500 grams (ml) of water to make a 50% moisture sample. If you start with 1000 grams of soil that contains 40% moisture, for example, how much more water will you add to make the sample to 50, 60, 70, 80 and 90% moisture?

Does this help? I will post more comments as I have time.

Donna Hardy

[trexzert]

I've completed 3 days of my experiment so far and found that the containers you buy in the stores for example 500g of food doesn't means that that container can hold only 500g. When my parents bought 6 700ml containers, they were smaller than the container that held 500g of food. I've learned a lesson from that. For the porous bags, the holes on them are a little big. This might ruin the experiment right?


Note: My sample size is 3....so I'm forced to use a small amount of banana peels. In my case, its 3 per container.

OH now I understand about sample size. Great. I only need to do this experiment once then since 3 sample sizes are done at once per container. So I need to wrap each banana peel with a porous bag.

I guess I'll restart. The teacher says we have until Jan 27. But if we need more time, we're allowed an exception if it's a project that takes time.

[donnahardy2]

Hi Trexzert,

It's nice to hear from you again! Thanks for sharing the information on the food containers. You always learn something when doing a science fair project, even if it's not what you thought you would learn. I'm not sure you need to restart, but I can't tell exactly what you did. If you put all 3 banana peels in one bag, just take them out and put them in separate bags. The holes won't be too big unless the banana peel can fall out of the bag. Rebury the banana peels and make sure they are in contact with the soil. You should take notes in a notebook during your experiment, so you can just write down what happened. If you do the same to all of the containers of soil, it won't affect the outcome of your experiment. How many containers of soil do you have?

Donna Hardy

[trexzert]

I have 4 container of soil.

If the sample size is 3, it doesn't mean that I have to redo an experiment 3 times right? 1 sample size in my experiment means 1 banana peel per container that contains a different amount of moisture. So if there were 4 banana peels per container, the sample size would be 4?

[donnahardy2]

Hi Trexzert,

Thanks for confirming your experimental set-up. You have 4 containers, each with 3 banana peels, and you will remove one banana peel from each container to determine its dry weight each time you do the testing. So for each container, you will have 4 data points to plot on your graph (time 0, day 7, 14, 21, for example). You will have one banana peel for each experimental data point. When you write up your results, you could say your total number of banana peels per container is 3, and that sample size is one (banana peel per data point) as that will be clearer to the science fair judges. If you waited until the end of the experiment and tested all 3 banana peels at the same time, then your sample size would be 3.

Since your project is due soon, it's not too early to write the other sections of your board. You should be able to do the title, question, hypothesis, background, materials, procedure and bibliography now. Look at the original assignment your teacher handed out and make sure you will include everything that is required. Let me know if you have any questions.

Donna Hardy

[trexzert]

I didn't know I had to wrap each banana peel with a porous bag so me and my parents came to a solution. Use plastic bags and poke numerous holes with a toothpick and use that as a porous bag. Will this work?

Also, my teacher told me I have to measure the dry weight of the banana. So every 3 days (Yes its 3 days now instead of per week) I'll have to mircowave the banana peel at school so that the added water in the beginning of the experiment would be gone. I would measure it then discard it. I made sure each banana peel weighted exactly 50 grams so when I measure it after, I can accurately know for sure.

[deleted-71447]

"me and my parents came to a solution. Use plastic bags and poke numerous holes with a toothpick and use that as a porous bag. Will this work?"
There is no perfect solution to this problem, but I think you will get better results with a more porous container, like a plastic mesh. If you use plastic bags, even with toothpick holes I expect the plastic film will inhibit transfer of gas, moisture, and organisms, all of which are very important to decomposition. That design of a plastic film/bag with holes is more commonly used to allow some gas transfer but to keep moisture contents high (for example, when growing edible mushrooms). Also, large-sized decomposers like sow bugs might not be able to fit through the toothpick holes. I believe you want a barrier that contains your peels, but also allows moisture content and organisms to move freely between the soil and the peels.

One option would be the plastic mesh bags used to hold vegetables like garlic:
http://www.global-b2b-network.com/direc ... Garlic.jpg
These holes might still be too small to allow passage of big decomposers like sowbugs, but they would, at least, allow free transfer of water and smaller organisms. Maybe there are some other similar solutions out there. I expect the other experts will have more ideas. Good luck!

Chris

[donnahardy2]

Hi Trexzert,

Chris has given you a really good solution for the porous bags; however, don't change your experiment if you have already set it up. The banana peels will decompose if moisture and microorganisms can come in contact with the banana peels. However, your plastic bags with holes poked in them will also work for a controlled experiment. If all of the boxes contain the same set-up, except the moisture content, then you will have a good experiment to test your independent variable (moisture). Your using a 50 gram sample of wet banana peel to start was an excellent idea.

I assume you are using a 3-day interval between tests because of the short amount of time available to complete your experiment. One possible outcome of your experiment is that you might not see a great deal of degradation (loss of dry weight) of the banana peel, but don't worry about this if it happens. Your experimental design a good and this should be a great project.

Let us know about your results.

Donna Hardy

[trexzert]

I made an amazing discovery and I don't believe it. In the beginning of my project, banana peels in each container had the total weight of 150grams. After 6days, I measured it and here is the results.

0% water 145grams

20% water 101grams

40% water 114grams

60% water 132grams.

I am wondering if this is possible. The banana peels in the container with 20% water lost the most weight.

[deleted-71447]

Hi trexzert,
Congratulations! You have demonstrated that it is possible. Your challenge now is to do a thorough analysis of the data, and to explain why you got the results that you did.

I have a couple of questions to help understand your results:

When you write "60% water" does this mean 60 g of water per 100 g of soil + water, or 60 mL water per 100 mL of soil + water, or something else? I recommend that you give the exact units of measurement in your report, because "%" can be interpreted in different ways, each with a different meaning and different implications for your results.

For the weight of the peels, are those all dry weights? Did you dry the peels before adding them to the containers, and before weighting them on day 6?

Looking forward to hearing more.

Chris

[donnahardy2]

Hi Trexzert,

This is wonderful! You have some actual data. I think you have discovered something new. Now, as Chris has explained, you just need to explain your results. We had discussed a number of options on setting your experiment, and I'm not sure exactly what you did, but here's one possible explanation.

Please confirm if this is what you did:
1. Dry all dirt samples overnight in the oven (0% water)
2. Add 20, 40 and 60 grams of water per 100 grams of soil for the 20, 40 and 60% samples.
3. Buried 150 grams of wet banana peel in the dirt samples.

If this is what you did, then it looks like the moisture from the banana peel was adsorbed by the drier dirt. This could explain the results from the 20, 40, and 60% boxes. The 0% moisture result is not consistent, so perhaps this banana peel did not make good contact with the soil for this sample. Are you going to rebury the banana peels and continue the experiment for a few more days?

Did you observe any mold growth or any physical changes in the banana peel? Does the banana peel smell like it is rotting? These changes would indicate that microbial growth is occurring that is degrading the banana peel. Or, do the banana peels just look drier than they did before? This change would help confirm the drying explanation.

Please let us know exactly how you prepared the soil for the 0, 20, 40, and 60% moisture boxes, whether the banana peel looked like it was being consumed by microorganisms, or if was just dried out. You are going to have a complete project here, but you will just have some work to explain your unexpected results.

Donna Hardy

[trexzert]

All correct except I used 500grams of dry soil per container. The banana peels in the container with water smelled of rot and turned fully black. The soil in the 40% and 60% container were very wet.

[deleted-71447]

I agree with Donna that the current mass changes may have more to do with changes in water content in the peels than with actual chemical decomposition of the peels. I'm not sure if your experiment is completed, but at the end of the experiment, after you take one final wet weight of the peels, will you dry them in the oven and re-weigh them? That would allow you to estimate the mass % of water in the peels at the end of the experiment, and will help to distinguish desiccation from decomposition.

The absorption of water by soils under different water contents can be complex and unpredictable. For example, intuition tells us that dry soils will absorb water more quickly, but some soils become resistant to absorbing water when they are very dry. Organic rich soils, like potting soils, are particularly odd. You might have noticed that when you water a very dry houseplant, the water will sometimes run across the surface of the potting soil before it soaks in. So, it is possible that your 0% water by mass soil might, over some time span, absorb water more slowly than the 20% water by mass soil. Whatever you used to hold the peels could also affect water absorption and transfer.

Another factor to consider is that water chemistry can change dramatically as the water content in the soil changes. It sounds like your 60% by mass treatment may have been water saturated (all pore space in the soil filled by water) in some or all of the soil. If you are using a very organic rich soil, like potting soil, saturated conditions can result in consumption of available oxygen in the soil, which tends to slow down decomposition. This is one reason that peat tends to accumulate in wetland soils. At the opposite end of the spectrum, in very dry soils, decomposition can also be relatively slow.

It's interesting to hear about your results. Thanks for keeping us posted.

Chris

[donnahardy2]

Hi Trexzert,

I am hoping you can continue your experiment for just a few more days because your results are very interesting. Chris has given you some valuable information to explain your results. The rotten smell and black color indicate that microorganisms are growing in your banana peels. Since you sterilized the soil in the oven overnight, where did the microorganisms come from? Have you seen anything furry growing on the banana? This would indicate the growth of mold. You should include a written description of the banana peel in your results.

For your final data point, you will need to take 150 grams of fresh banana peel and dry it gently in the oven. You may have already done this, as this would represent the dry weight of the banana peel Then, as Chris suggested, at the end of the experiment, weigh the sample wet, and dry it and get the dry weight. The difference in the dry weight of the first and last data point would represent the effect of burying the banana peel in soil.

Since your science project is due soon, you can go ahead and complete all of the sections for your board, including the title, question, hypothesis, background, materials, methods, and bibliography sections. Save room in the center of the board for the graph and description of your results, and save space for a discussion of your results. How are you planning to graph your results? Chris and I have given you ideas for the discussion section that might help explain the final results. This is a really great project, so do spend the time to prepare your board so your teacher and science fair judges will understand exactly what you have done. Go back to the original assignment that your teacher gave you weeks ago and make sure you have included everything on the list. And, let us know if you have any questions on the write up.

Donna Hardy

[donnahardy2]

Hi Trexzert,

How is your project going? Did you complete it? We are very interested in knowing about your final results and your conclusions. Let us know.


Donna Hardy

[trexzert]

Apologies for my long absence.

I have astonishing results.

0% - 56 grams

20% -46 grams

40%- 48 grams

60% - 55 grams.

Those are the combined weight of each 3 peels per container after drying them completly.

I can't believe how much weight moisture takes up.

[donnahardy2]

Hi Trexzert,

It's great to hear from you again! Thanks for posting your results. You are right, the banana peels do contain a lot of water. Do you think the difference in weight between 0 &60% water, and the 20 & 40% water samples represents the amount of weight lost due to degradation by microorganisms? Does this mean that 20 and 40% water is the best concentration for composting? What were your conclusions?

Have you entered your project in the science fair yet?

Donna Hardy

[trexzert]

Revised again. Although, I think I can erase one sentence in my question.

Question: Does moisture affect the degradation speed of banana peels? Will having more moisture affect it’s degradation speed?

Hypothesis: Higher moisture content in the soil will promote faster degradation rates.

Materials:
-4 plastic container of equal size. Should be able to fit in 750g or more
-12 banana peels.
-2000 g of soil (8cups)
-an electronic scale or balance that can measure to the nearest hundredths
-oven with baking sheet.
-4 porous bags that can fit 3 banana peels
-container that has measurements in mL
-12 plastic bags
- 1 control banana peel (used at the end of experiment)
Procedure:

1. Put 2000g of soil in the oven and set the heat to 200 degrees for 20 minutes. Let it cool.
Note: Make sure your parent or guardian agree to this before trying it. Also, if there is dead organic substances in the soil like grass, there will be an unpleasant smell when you take it out of the oven.

2. Place 3 banana peels in a porous bag and seal. Then place it in one container. Do the same with the other bags and peels. You should have 4 containers that holds 3 banana peels each in a porous bag.

3. Place in 2 cups (500g) of soil into each container.

4. Label your plastic containers from 0%,20%,40%,and 60%. Now, get out the container that has measurements in mL and fill in water equal to 20% of the amount of substances that is held in the plastic container labeled 20%. ( If you put in 500g of soil in the plastic container, then 20% of 500g is 100ml. So, you would fill in that container with 100ml of water.) For the container labeled 40%, fill in water equal to 40%, which in this case is 200ml. Then on the container labeled 60% fill in water that equals to 60% which is 300ml. For the container labeled 0%, do not add any water into it.

5. You must not put on the lids in any of the container. Place the 4 containers at room temperature, at a safe place. Do not put it outside.

6. Every 5 days, take out each container’s porous bag that holds 3 banana peels and weight it. Make sure no soil is lost, so wrap the container with a big plastic bag. When your taking out the peels, soil that falls out will be in the that plastic bag. Gently shake off lose dirt and then measure the weight in grams. Then put the peels in the porous bag back into the container and any soil in the plastic bag. Do the same with all the other ones.

7. After 15 days, make your final measurement by doing step 6. Now, you also have to oven dry all the peels and measure it again. This will give the weight of the dry banana peels. We have to use the control now, and that's a peel weighing the exact amount as the other peels. Oven dry it so that once we weigh it, it shows the dry weight of a peel that didn't face degradation. Compare this peel with the other peels and see the weight difference.

[trexzert]

My project is over. Thanks to all that helped. In a competition from gr 8-10 at my school, I was ranked got top 10.