Hands-on Activity: Composting – Nature's Disappearing Act

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

A photograph shows a pile of trash — cans and scraps of metal — that are in various stages of breakdown.
Students explore biodegradability.
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Copyright © Microsoft Corporation 1983-2001

Summary

Students explore the concept of biodegradability by building and observing model landfills to test the decomposition of samples of everyday garbage items. They collect and record experiment observations over five days, seeing for themselves what happens to trash when it is thrown "away" in a landfill environment. This shows them the difference between biodegradable and non-biodegradable and serves to introduce them to the idea of composting. Students also learn about the role of engineering in solid waste management.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Engineers are challenged with the problem of quickly and efficiently composting landfills, turning food, yard and animal waste into high-nutrient soil. By designing landfills to decompose garbage quickly (5 to 10 years), engineers create environmentally friendly ways to eliminate trash and generate landfill gas to produce electricity.

Learning Objectives

After this activity, students should be able to:

  • Define biodegradable and non-biodegradable.
  • Explain how engineers work to reduce solid waste.
  • Gather and record data and observations based on a landfill experiment.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Represent real world and mathematical problems by graphing points in the first quadrant of the coordinate plane, and interpret coordinate values of points in the context of the situation. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Waste must be appropriately recycled or disposed of to prevent unnecessary harm to the environment. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Models are used to communicate and test design ideas and processes. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Investigate and identify two or more ways that Earth's materials can be broken down and/or combined in different ways such as minerals into rocks, rock cycle, formation of soil, and sand (Grade 3) Details... View more aligned curriculum... Do you agree with this alignment?
  • Use evidence to develop a scientific explanation about one or more processes that break down and/or combine Earth materials (Grade 3) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Each group needs:

  • 2-liter bottle, cut in half so the bottom half can serve as a stand to hold the top half turned upside down
  • 3 cups soil; garden soil works best; avoid using potting soil because it does not have all of the organisms and bacteria that help with decomposition
  • ¾ cup water
  • 1 sheet paper, torn into small pieces; recycled paper or newspaper works
  • 2 lettuce leaves, torn into small pieces
  • 1 apple, sliced or diced into small pieces
  • 2-3 plastic food containers, such as yogurt cups; cut into small pieces about ½ inch squares
  • rubber or latex gloves, one pair per student
  • 2 spoons or Popsicle sticks
  • measuring cups, in sizes: 1 cup, ½ cup, ¼ cup
  • masking tape, 6-inch strip
  • marker or pen
  • Nature's Disappearing Act Worksheet, one per student

For the entire class to share:

  • 2 extras of the group landfill model setups, to serve as experimental controls
  • rags, paper towels, broom, dustbin, sink - for clean up

Introduction/Motivation

What do we mean when we say something is "environmentally friendly" or "environmentally unfriendly"? (See what students think.) We are deciding whether or not it causes more harm to the environment than good. More specifically, we classify waste in the environment as biodegradable or non-biodegradable. Biodegradable items are usually considered "environmentally friendly."

What do we mean when we say that something is biodegradable? (Listen to student ideas.) We mean that it is a substance that can be broken down by natural environmental processes into basic elements such as carbon dioxide, nitrogen and water. This may seem simple, however, nature only breaks down things that nature creates. For example, nature does not make plastic and is unable to easily break plastic down into its basic components. If nature cannot break something down into basic elements, then we label it as non-biodegradable. Plastic is considered non-biodegradable. Sometimes, biodegradable items do not break because they are deprived of environmental conditions or (to help you remember), LAWS: light, air, water and soil.

Much of the waste in our landfills is biodegradable. However, many of our current landfills do not permit naturally biodegradable things to decompose because they are deprived of light, oxygen and often moisture. Sometimes this is done on purpose to prevent gas production in landfills, but it means the biodegradable trash never goes away (does not decompose).

Composting is a way to decompose food, yard and animal wastes into new soil. Some engineers are specialists in optimizing the process so that biodegradation takes place more quickly and efficiently. This means that the engineers devise ways to make composting and landfills work better. This helps us manage the garbage and waste in a way that is less harmful on the environment and is more environmentally friendly. One idea is to do composting in your own yard with your own kitchen and yard waste. Composting reduces the amount of trash that you send to a landfill and creates a rich soil amendment to add back to your yard to benefit the plants and landscaping. The Seattle Zoo in Washington composts elephant manure and gives it away free to gardeners as "Zoo Doo."

Who knows what a "model" is? (Listen to student ideas.) One type of model is what engineers do when they want to really understand something and make it better, and they don't want to make it full scale for testing. Today we are going to make our own model landfills and look at how composting works in a model environment.

Vocabulary/Definitions

biodegradable: Substances that can be broken down by natural environmental processes (involving microorganisms) into basic elements such as carbon dioxide, nitrogen and water.

composting: A process in which food, plant, yard and animal waste decomposes into new soil. Engineers often work to optimize the process so that biodegradation takes place more quickly and efficiently.

decompose: To break down into basic elements. Often called "rotting."

decomposer: The bacteria, fungi, earthworms, etc. that eat the remains of dead plants and animals and release basic elements (like nitrogen) back into the environment.

model: (noun) A representation of something for imitation, comparison or analysis, sometimes on a different scale. (verb) To make something to help learn about something else that cannot be directly observed or experimented upon.

nitrogen cycle: A natural process that recycles nitrogen back into the environment. Plants absorb nitrogen compounds from the soil; animals eat the plants, passing the nitrogen along the food chain; when animals and plants die they decompose, with the help of decomposers, and the nitrogen compounds again become part of the soil. (Note: The sulfur and phosphorus cycles are similar.)

organic: That which is created from living organisms.

Procedure

Timing Note

Plan on about 95 minutes total to conduct this activity over five days, with the following breakdown:

Day 1: 45 minutes for teams to make landfill models

Day 2: 10 minutes for observations

Day 3: 15+ minutes for observations

Day 4: 10 minutes for observations

Day 5: 15+ minutes for observations and wrap up

Before the Activity

  • Gather materials and make copies of the Nature's Disappearing Act Worksheet, one per student.
  • Make available a spot to keep the "landfills" during the multi-day observation period. Find a place that receives sunlight, but where any odor is not bothersome.
  • Keep the four "garbage" items (apples, lettuce, plastic and paper) separate from each other. (If you are doing this activity as an extension of Lesson 4's This Landfill Is a Gas activity, do not mix the garbage as instructed for that activity.)
  • Set up controls to compare the landfill models. Follow the same activity procedure to set up two extra landfill models. For the first control model, do not cover the "garbage" samples with soil, but do continue to sprinkle them with water (this sample will be continuously exposed to light). For the second control model, cover and water the "garbage," but do not disturb the topsoil at all until the end of the entire observation period (this sample will not be exposed to as much air). Place the controls in a sunny spot for the course of the activity. Ask students to compare the biodegradation in their landfills to the controls.
  • Check out the following book from the library: The Magic School Bus Meets the Rot Squad: A Book about Decomposition, by Joanna Cole.

With the Students

  1. Read aloud to the classThe Magic School Bus Meets the Rot Squad: A Book about Decomposition.
  2. As a class, discuss the ideas of biodegradable and non-biodegradable. What are some examples of each? What are some things that are required in order for items to biodegrade? (Answer: Light, moisture, oxygen/air.) Discuss why biodegradation is an important part of nature. (Answer: It helps get rid of [recycle] waste in the environment. It keeps the nitrogen cycle and thus the circle-of-life going. If desired, introduce/review the nitrogen cycle at this point.) Why is biodegradation an important idea related to solid waste management? (Answer: Much of the waste in our landfills is biodegradable, but many landfills do not permit even biodegradable things to decompose because they are deprived of light and oxygen and often moisture. This is done to prevent leaching and methane production in landfills.)
  3. Show students the control "landfills" and explain the activity.
  4. Divide the class into groups of four students each. Distribute the supplies: worksheets, soil, already cut apart 2-liter plastic bottles, masking tape, gloves, water, and a small amount of each of the four "garbage" samples.
  5. Direct each group to write the names of its group members (or a group name) on the masking tape and place it on the top portion of the 2-liter bottle.
  6. Have all students put on their gloves.
  7. Have the students place the top portion of the 2-liter bottle upside down in the cut off bottom half of the bottle. The bottom serves as a stand that helps to keep the model container upright.
  8. Direct students to place 2 of the 3 cups of soil inside the bottle.
  9. Have students lightly draw a large X on top of the soil so that they have 4 equal areas outlined in their miniature landfill. Direct them to place one "garbage" sample in each section on top of the soil.
  10. Direct students to draw diagrams of their models on their worksheets, labeling what test garbage sample is in what location. This is one way engineers and scientists keep good records their plans and the design of their projects and experiments.
  11. Direct students to sprinkle the remaining soil on top of the "garbage" items.
  12. Have students sprinkle ¾ cup water over the landfill. In this model of a landfill, the water simulates rainfall.
  13. Next, direct students to write predictions on their worksheets. Which test items will break down first? Which will break down last? Explain their reasonoing.
  14. Place all the "landfills" in a location where they will get some sunlight and be undisturbed.
  15. The next day (Day 2), observe, but do not disturb the landfills. Have students record their observations on their worksheets. Does anything appear to have changed in the bottle?
  16. On Day 3, direct students to put on their gloves and use a spoon or wooden stick to gently scrape back the top layer of dirt. What do they notice about the garbage in their landfill models? Have any items started to biodegrade? How do they know? What is the evidence for their conclusions/observations? Remind them to record their observations on their worksheets. Then have them carefully replace the top layer of soil and sprinkle another ¾ cup water over the soil..
  17. The next day (Day 4), observe, but do not disturb the landfills. Have students record their observations. Does anything appear to have changed in the bottle?
  18. On Day 5, direct students to put on their gloves and use a spoon or wooden stick to gently scrape back the top layer of dirt. What do they notice about the garbage in their landfill models? Have any items started to biodegrade? How do they know? What is the evidence? Remind them to record their observations.
  19. Direct students to complete the worksheet comparison and conclusion questions.
  20. Have groups work together as engineering teams and come up with a sales pitch for a product to dispose of biodegradable or non-biodegradable waste. Have them brainstorm the product, incorporate what they learned from the model experiment, prepare the sales pitch, and present it to the rest of the class.

Attachments

Safety Issues

Be sure to wear gloves to dispose of the model landfill contents at activity end.

Troubleshooting Tips

Eliminate some distractions and mess by measuring out each group's soil and water amounts before the activity.

Have rags, paper towels, broom and dustpan on hand since water and soil can get messy.

Assessment

Pre-Activity Assessment

Discussion Questions: Lead a class discussion to assess students' base understanding of the activity topics. Ask the students:

  • What do we mean by "biodegradable" and "non-biodegradable" items? What are some examples of each?
  • What are some things that are required in order for items to biodegrade? (Answer: Light, moisture, oxygen/air.)
  • Why is biodegradation an important part of nature? (Answers: It helps get rid of waste in the environment. It keeps the nitrogen cycle and thus, the circle-of-life going. It recycles what might be consider unwanted materials into valuable resources.)
  • Why is biodegradation an important idea related to solid waste management? (Answer: Much of the material in our landfills is biodegradable, such as food, plant and yard waste, but in many current landfills these biodegradable items never decompose because they have no access to light, oxygen and moisture. This is done to prevent leaching and methane production in landfills.)

Activity Embedded Assessment

Diagramming: Ask students to draw a descriptive diagram of their landfill models in the space provided on the worksheet. Remind them to label each of the garbage test samples.

Predictions: Ask students to write down their predictions on the worksheet, indicating which test items in the model landfill they expect to break down first and last. Have them explain their reasoning.

Observations: Have students record their observations as prompted by their worksheets.

Post-Activity Assessment

Worksheets: Have students complete the last four questions on their worksheets. Review their answers to assess their depth of comprehension of the activity concepts.

Sales Pitch: Working together as if they are engineering teams, have student groups come up with a sales pitch for a product to dispose of biodegradable or non-biodegradable waste. Have them brainstorm the product, prepare the sales pitch, and present to the rest of the class. Their presentations reveal their understanding of the activity content.

Activity Extensions

Have each group suggest and test additional, different items as garbage samples.

Continue the activity longer than five days to see if some of the items eventually biodegrade with more time. Have students graph their data on the different items and degradation time. What patterns are revealed in the graphs?

Have students layer their landfills: soil, garbage, soil, garbage, etc. Have them compact it tightly. Doing this is a more accurate model of of a real-world sanitary landfill. By comparative testing, evaluate whether this affects how quickly the items biodegrade.

Build and maintain a classroom/school compost bin, working with the cafeteria staff and grounds crew.

Activity Scaling

  • For third-grade students, set up the landfill models before the activity. Or place the garbage in a few models as a class demonstration and do the observations as a class activity. Alternatively, use one model for each test garbage type, or compare fewer items, for example just grapes and plastic.
  • For fifth-grade students, use metric measurements (l and ml), instead of cups. And, look more carefully at the conditions required for organic decay. Have groups explore these requirements by giving their landfill models different amounts of light, water or air exposure. Additionally, explore the effect of temperature and water acidity.

Additional Multimedia Support

Check out the slide show about composting for kids at http://aggie-horticulture.tamu.edu/kindergarden/kidscompost/cover.html

References

Blashfield, Jean F. and Wallace B. Black. Recycling (SOS Earth Alert). Childrens Press, Inc., 1991.

Cole, Joanna. The Magic School Bus Meets the Rot Squad: A Book about Decomposition. New York, NY: Scholastic Inc., 1995.

Goodman, Billy. A Kid's Guide to How to Save the Planet. New York, NY: Avon Books, 1990.

Prentice Hall Science. Ecology Earth's Natural Resources Activity Book. New Jersey: Prentice Hall, Inc., 1993.

Contributors

Amy Kolenbrander; Jessica Todd; Malinda Schaefer Zarske; Janet Yowell

Copyright

© 2005 by Regents of the University of Colorado

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the DOE or NSF, and you should not assume endorsement by the federal government.

Last modified: July 5, 2017

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