Experimenting with biodegradability

Introduction: (Initial Observation)

There is a great concern for the environment nowadays. A current environmental issue that confronts the scientists, politicians and educators is biodegradability. We dispose materials every single day, but where are these disposed materials really going? What happens when we throw something away?

In a large city like New York, 11,000 tons of garbage is produced each day. The annual production of municipal garbage in the US, in the year 1997, was 217 million tons.

The problem that we face is continuous accumulation of garbage that is also growing at a very high rate. If the materials decompose or degrade, they will become soil again; otherwise, we will eventually run out of space for storing garbage.

In this project you will test different materials to see which ones are bio degradable.

Information Gathering:

Learn more out about Biodegradability. Read books, magazines or ask professionals who might know in order to learn about the factors that affect biodegradation of different material. Be sure to keep track of where you got your information.

Why do we study biodegradability?

Years of research in chemistry, polymer science and technology have produced new plastics, which have made life easier and more convenient. Polymers have been developed and are able to retain their strength by resisting the break down of their molecular composition caused by light, air and water. This enabled consumer products made of these polymers to be very effective in many applications. Because of their light weight and durability, plastics have become a commonplace material in the lives of consumers.

Since many plastics are used in ‘throw-away’ packaging applications, an environmental issue has arisen concerning the use, recycling, and disposal of these materials. Can we reduce our landfill needs by reducing the amount of plastics that we discard? In order for material to decompose, chemical bonds must be broken by bacteria, fungi, microorganisms, water in the soil, sunlight or by some other means. From past studies, we see that this process takes time, and time seems to be running out for Planet Earth. What are some possible answers to the problems of disposal? Is degradability and biodegradability the answer?

What material are biodegradable?

Collect some natural plant products such as pieces of potato, lettuce, apple, banana, bread and candy. You also can include things like paper, ground coffee and tree leaves.

Think about how these things are different and similar. They are all natural products and grow as plants.

What happens to apples, bananas or bread when they “sit around” for a long time. Apples rot. Bananas get soft and turn dark. Bread gets hard and moldy. What about tree leaves? They turn color, fall to the ground and gradually decompose. If you can find a leaf skeleton, you can see an example of natural decomposition.

Get some latex balloons. Do you know what they are made from? They are not plastic! Balloons are natural products, similar to candy. Balloons are made from rubber tree juice. Candy is made from the juice of the sugar cane. Rubber trees are tapped to get the latex.

Rubber latex balloons are degradable because they are a natural plant product. These balloons are made from a milky substance from the rubber tree and decompose by natural processes such as exposure to soil bacteria, sunlight, moisture and atmospheric oxygen.

To demonstrate biodegradability of latex balloons, you will need:

1. A plant light. A 150-watt GE “gro & sho” light.
2. A shallow pan, aluminum pie plate, or Petri dish.
3. Garden soil and peat moss, two centimeters deep.
4. About 20 grams of composting agents.

Mix the compost with the garden soil/peat moss. Wet the mixture well. Next, get a few balloons and cut them into several pieces before burying in the mixture.

Place the plant light about 20 centimeters (about 8 inches) above the pan. Add water to the pan daily to keep the soil mixture moist.

Bacteria live in the soil, and that’s what eats away from the balloon molecules. Ultraviolet light from the sun (represented by the grow light) and oxygen also combine to break down the balloon. The physical appearance of the balloon changes as it decomposes.

Examine the balloons in the pan periodically. After about 20 hours under the light they should begin to show considerable degradation. After 60-70 hours, the balloons should be largely disintegrated. You can compare the deteriorating balloons to those left in the package in which they came.

In biodegradation, bacteria do the main work, but there are other types of degradation as well. The UV radiation from sun light, moisture, chemicals and oxygen in the air are all degradation factors. For example most metals rust and break down to metal oxide. Some natural polymers and organic chemicals break down by the sun light.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this investigation is to experiment, demonstrate and understand biodegradability and find answers to the following questions.

• What materials are biodegradable?
• What factors affect biodegradability?
• What factors affect non-biological degradation?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

For the question of what materials are biodegradable?, the type of material is an independent or manipulated variable. Biodegradability is the dependent variable.

For the question of what factors affect biodegradability? the independent variable is the factors that may affect biodegradability. Dependent variable is biodegradability.

For the question of what factors affect non-biological degradation? the independent variable is the “factors” that we test and the dependent variable is decomposition or degradation.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is only a sample hypothesis, and you should come up with your own.

I think all material, other than plastics, are biodegradable. My hypothesis is based on my gathered information and my previous observations. I have seen that pieces of paper, pieces of wood, even meat and metals disappear in the soil, but I have not seen a plastic disappear in the soil.

I think the factors affecting biodegradability are the same factors needed for bacteria growth. Mild temperature, water and food are the main factors.

I think sunlight, oxygen, moisture and some chemicals such as salt can contribute to degradation.

*Only a sample. Be sure to form your own hypothesis based on your data.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Biodegradability and recycling

Introduction:

Materials that are not biodegradable must be recycled, otherwise they add up and continuously extend the level of pollution in the soil. Does the knowledge of biodegradability improves awareness of recycling? In this experiment you will observe and compare how well different items biodegrade over time.

Material

• Large fish tank (10 to 20 gallon);
• five gallons of moistened soil (but NOT potting soil);
• plastic wrap;
• strapping tape;
• pieces of aluminum foil,
• cloth,
• cracker,
• eggshell,
• orange peel,
• soap
• Styrofoam;
• a plastic spoon;
• a paper clip;
• a glass jar;
• a wooden pencil with an eraser.

Procedure

Cover the bottom of the fish tank with about four inches of moist soil. Place the trash on top of the soil. Cover the trash with another five inches of soil. Seal the tank with the plastic wrap and secure with tape. Place the tank in direct sunlight (can be substituted with UV light).

Unseal the tank once a week to allow oxygen to enter, then reseal. Uncover the trash after three to four weeks and observe any changes. Rebury the trash and reseal the tank for another month (continue to unseal and reseal the tank once a week). Uncover the trash again and observe any changes.

Record your observations.

If you have access to a small scale, you may record the initial weight of each object and final weight of whatever remains from each object. Both added weight and lost weight can be indications of degradation.

Using the results of your experiment answer the following questions:

Identify three items made from each of the following materials: wood, plastic, metal, fabric, glass, paper and organic matter.

Which items do you think are recyclable?

Discuss the items that nature recycles and how.

Discuss what items decompose during the experiment and how quickly they do so.

Experiment 2:

Solid – Non-Degradable – Here to Stay

Introduction:

The high rate of production of garbage is a major problem for many cities and states. Some cities have to carry their garbage to other cities and often other states because they practically have no more space to dump garbage.

To reduce this problem, we need materials that disintegrate and becomes soil. It does not matter how.

Some materials are degradable, but they are not bio-degradable. Such materials do not need bacteria for degradation. Heat, air, moisture and chemicals will help these materials to degrade. In this experiment we will test different solid materials to see which ones are degradable.

Material:

• 8 pieces ( 5 cm square) of materials to be tested such as paper cup, plastic milk container, newspaper, paper bag, poly (vinyl chloride) (PVC), plastic bottle, aluminum foil, etc.
• 16-250-mL beakers
• 1 hot plate
• 1 pair of beaker tongs
• 1balance (reading to two decimal places)
• A strong salt solution or simulated sea water
• water
• marking pen or pencil
• goggles
• aprons
• hot pads or gloves

Procedure:

1. Obtain 16 250-mL beakers and label 8 beakers “water” and 8 beakers “salt water.”
2. Obtain 2 pieces each (5cm square) of the materials to be tested such as paper plates, paper cups, newspaper, aluminum foil, PVC bottle, milk container plastic.
3. Weigh each piece of material and record the mass in a table.
4. Fill 8 beakers with 100 mL of water and 8 beakers with 100 mL salt water.
5. Place one piece of each material selected in a beaker of salt water and one in a beaker of water.
6. Place the beakers on the hot plate and heat to boiling. Continue heating for 15 minutes.
7. Note any changes in each of the materials as they are heating.
8. After 15 minutes of heating, remove the beakers from heat and with your forceps remove each piece of material from the beakers and place the materials on a paper towel to dry.
9. The materials may have to dry overnight.
10. Reweigh the materials and record the masses in the table.
11. Compare your results and answer the following questions

Questions:

• What was the purpose of heat in this experiment?
• What were the changes observed in the water and salt water?
• What do the changes in the water mean for the environment?
• If these materials were degradable, what would you expect to see? If these materials were biodegradable, what would you expect to see?

Sample results table for this experiment: (g=grams)

Experiment 3:

Plastic Dispersion – Gone But Not Forgotten

In many products, plastics are dispersed in a liquid. Wood glue and water based paints are often of this type. They are emulsions of plastics in water. Calcium chloride is able to change the balance in an emulsion and separate the plastic from water. Calcium nitrate can do it better, but it is harder to get. Calcium chloride can be purchased from many hardware stores. It is commonly used to melt snow or ice.

Material:

• 2 grams of calcium chloride dihydrate, CaCl2 2H2O  (From hardware store)
• 100 mL water
• Latex paint (not oil based)
• thermometer
• hot plate
• glass stirring rod
• 2-250-mL beakers
• balance ( reading to two decimal places)
• 1-100-mL graduated cylinder
• goggles
• aprons
• hot pads or gloves

Procedure:

1. Weigh 2 grams of CaCl2 2H2O and place in a 250-ml beaker. Add 100 mL of water. Stir and place on a hot plate.
2. Heat the CaCl2 solution to between 85°C to 90°C .
3. While the solution is heating, obtain another 250-mL beaker and place 20 grams of latex paint in the beaker. Add 10 mL of water to the beaker and stir until homogeneous.
4. When the CaCl2 solution reaches between 85°C to 90°C , slowly add the diluted paint to the CaCl2 solution while on the hot plate.
5. Continue to heat the mixture for 10 to 15 minutes, stirring constantly.
6. Remove from the hot plate and allow to cool.
7. Observe the material in the beaker and complete the following questions.
8. Fill up the following results table to show what percent of paint is solid.

Questions:

• Describe the appearance of the CaCl2 solution and the paint emulsion upon mixing.
• Describe the final appearance after heating the solution for 15 minutes between 85°C and 90°C.
• Do you think you have the same material that you began with? Why?
• Where do you think the precipitate came from?
• What does this tell you about paint?
• Is this a qualitative or quantitative observation? Why?
• If a plastic disperses in a liquid, does this mean it is degradable?
• If a plastic disperses in a liquid, does this mean it is biodegradable?

If CaCl2 is not available, acetic acid may be substituted. Two mL of acetic acid may be added to 100 mL of water. The results would be the same. Please Note: When heating the acetic acid place the hot plate in a hood or heat the solution in a well ventilated room. The fumes created from heating acetic acid can be irritating to the respiratory tract and eyes. Vinegar is a 5% solution of acetic acid. You can use vinegar for this experiment after diluting it with the same volume of water.

Experiment 4:

In this experiment we will measure the amount of solids in latex paint. This is the part that is not degradable.

Material:

• 1-250-mL beaker
• glass stirring rod
• weighing dish
• pipette
• hot plate
• balance (reading to two decimal places)
• goggles
• aprons
• hot pads or gloves

Determination of the Percent Solids of a Latex Paint

1. In a 250-ml beaker, dilute 10 grams of paint with 20 mL of water.
2. Record the mass of a weighing dish in your results table
3. Add 1.5 to 2.0 grams of the diluted paint to this weighing dish.
4. Place the weighing dish on a hot plate and begin heating it at a low setting. Do not let the suspension splatter.
5. Record your starting time.
6. At one-minute intervals, remove the weighing dish from the hot plate and reweigh it. Record your reading in the proper place on a Data Table.
7. Place the weighing dish on the hot plate and continue heating and reweighing the material at one minute intervals until the mass of the dish remains constant for two consecutive readings.
8. Remove the dish from the heat and allow to cool. Take the final reading of the dish and calculate the percent solids.
9. Graph your data from Data Table.
10. Complete your observations and answer the following questions.

Sample Data Table and graph

Time (Minutes) Mass (grams)  0 2.87  1 2.48  2 2.16  3 1.86  4 1.61  5 1.40  6 1.32  7 1.31  8 1.30  9 1.30 10 1.30

Sample Results table

Questions:

• While heating the dish with the paint, what was given off?
• From your calculations in the experiment, what would be the percent of solids obtained for a solution of 10 grams of paint and 30 grams of water? 40 grams of water?
• Why did you weigh the dish at one minute intervals?
• What was the percentage of water in your sample of paint solution?
• From this experiment, what general conclusion can you make about degradability? biodegradability?

Milk could be tried instead of paint with the acetic acid. This could be filtered at the end and other activities could be developed.

In this activity, Determination of the Percent Solids, Elmer’s Glue® can be substituted in the place of latex paint.

Experiment 5:

Can we use organic solvents to dissolve plastics as a way of decomposing them? What will happen to plastics dissolved and disappeared in a solvent?

Material:

• balance (reading to two decimal places)
• 2- 400-mL beaker
• 1-100-mL graduated cylinder
• 100 mL of acetone
• 400 mL of water
• polystyrene packing peanuts
• glass stirring rod

Experiment:

1. Take a 400-mL beaker and fill it with 200-mL of water.
2. Add a few packaging “peanuts” to the water.
3. Observe the reaction of the water and the “peanuts.”
4. Fill another 400-mL beaker with 100 mL of acetone.
5. Weigh a few packaging “peanuts” and record their mass.
6. Take approximately 50 – 100 packaging “peanuts” and continually add them to the beaker with the acetone.
7. Observe what happens to the “peanuts” as each is added to the acetone.
8. Estimate the total weight of the “peanuts” added to the acetone.
9. Predict what would happen to the contents of the beaker when you would add 200-mL of water.
10. Add 200-mL of water to the contents of the beaker.
11. Filter the contents of the beaker and weigh the material.
12. Make your observations and answer the following questions.

Questions:

• What happens to the packaging “peanuts” when added to the beaker with water?
• What was the approximate mass of 5 packaging “peanuts.”
• What was your prediction of the number of peanuts that could be placed into the acetone in the beaker?
• What is the approximate mass of all the packaging “peanuts” that were added to the acetone?
• As the peanuts are placed in the acetone, describe what is happening?
• What do you think causes the “fizzing” heard?
• Does the acetone degrade the peanuts?
• What role does the water play in the experiment?
• If the plastic disperses in the liquid, does it mean that it is degraded? biodegraded?
• After you filtered the contents of the beaker, what was the approximate mass of the material?
• What can you conclude about the material you isolated in relationship to the starting material?

Materials and Equipment:

List of material can be extracted from the experiment section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

You need to calculate the percent of solids in experiment 4.

Write your calculations in your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Rubber latex balloons are degradable because they are a natural plant product. These balloons are made from a milky substance from the rubber tree and decompose by natural processes – exposure to soil bacteria, sunlight, moisture and atmospheric oxygen.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

1. What does degradability mean?
2. What does the term biodegradability mean?
3. Is biodegradability good for all materials? Why?
4. What things would you not want to be biodegradable?
5. What are the conditions required for biodegradability?
6. What are some ways in addition to biodegradability that will help the environment?

More experiments can be done:

1. Many companies are trying to capitalize on the biodegradability theme by offering “green” materials, i.e. their product as biodegradable. But are they really? Go through the supermarket and stores and list all of the products that claim to be biodegradable. Design possible ways to test their claim.
2. As part of the extension of experiment #1, select materials that you could subject to a long term exposure study. These materials could be buried, or put in a water-filled trash can for months, weighing the materials every so often to determine if they degrade.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Following resources have been used in preparation of this project guide.

http://concise.britannica.com/ebc/article?tocId=9357292&query=null&ct=null

Texas Natural Resource Conservation Commission

Argonne National Laboratory

Biodegradability Capsule

http://www.rohmhaas.com/company/plabs.dir/htmldocs/biodegrade.html

http://www.srpnet.com/community/education/experiments/bio.asp