(2 classes three months apart)

Students investigate what types of materials biodegrade in the soil, and learn what happens to their trash after they throw it away. The concepts of landfills and compost piles will be explained, and the students will have an opportunity to create their own miniature landfill in which the difference between organic and inorganic waste will become clear.

Waste management engineers use the process of biodegredation to minimize the amount of space that landfills take up. By burying layers of trash with other layers of soil, all existing waste is compressed under weight from above. For organic matter to decompose, however, aerobic bacteria, which needs to be exposed to air, is required. Thus, large machines are used to churn up and aerate top layers, allowing the organic matter that is present to decompose. biodegradable soil compost landfill A basic knowledge of soil and its components would be desirable, but no previous knowledge surrounding the process of biodegrading or decay is necessary. Explain what the term "biodegrade" means, and come up with a loose explanation of how the process works. Identify whether a certain object can biodegrade or not. Explain the difference between organic and inorganic materials. Explain how engineers apply what they know to facilitate waste management. What do you think happens to your trash after you throw it in a trash can? Where do you think it goes after it leaves your kitchen, house, or school? Most of your trash is delivered by some means (usually with a dump truck) to a local waste management site, or a dump. A waste management site is a specific plot of land, usually located near your town or city, that is designated to hold your community's garbage. Your trash usually gets there via a large garbage truck, which you may have seen coming to your house on certain days of the week. Now, what do you think happens to the trash while it is at the dump? Does it sit there unchanged forever, or do some items slowly rot? What happens to the trash that rots? Let me introduce to the class the concepts of biodegradation, organic and inorganic materials (included in the definitions below). At our waste management site, we will bury various pieces of trash and left-over food from all of our lunches in separate patches of ground. Then we will let all the different experimental sites "sit" for two to three months to allow biodegredation to occur (or not). Finally, we will dig into these sites to see what remains of our trash. To further the concept of biodegredation, let me provide the specific definition of "biodegrade". To "biodegrade" means to decay and become absorbed by the surrounding environment. Everyone should have heard of the term "decay", as in "tooth decay" or the decay of dead plants or animals. Perhaps you have even seen the decay or certain fruits or vegetables in your kitchen. Another example of decay occurs outside, when dead trees and leaves decay back into soil. The same is true for animals and insects that have died. These organic, or once living materials can turn back into soil because they are made up of the same tiny molecules and elements that soil is. Actually, almost any material that was once a part of a living organism is capable of decay. For example, the pencils that you write with and the paper you write on were once a part of a living tree, and are capable of decaying. Finally, it is important for us to discuss the concept of a compost pile before we begin our work. Have you ever seen or used a compost pile? If so, what did it look like? Compost piles are mounds comprised completely of organic waste and trash, and they are setup so that bacteria can help the material biodegrade back into soil as quickly as possible. Compost piles are left outside so that heat from the sun is able to encourage bacteria growth and designed to allow some air to enter the pile. If anyone has any questions about any of these related processes, like the difference between a landfill and a compost pile, feel free to ask before we begin the activity. Biodegradable materials, or pieces of organic matter, are those that can break down from larger molecules to smaller ones, much like in the process of rotting. Usually living organisms, in the form of bacteria, are what break apart these molecules. Biodegradables are beneficial for the environment because they are able to turn back into useful organic matter, like soil. Many products are now made with organic materials so that their disposal is more ecologically friendly, like various wrappers, bags and containers. Examples of organic matter are foods, food peels, egg shells, paper, leaves, and grass clippings. Materials that degrade can do so aerobically, with oxygen, or anaerobically, without oxygen. Once trash is thrown away, it is taken to a dump where it just sits and becomes buried with other trash. Thus, anaerobic biodegradation is accountable for some of the degrading that takes place at landfills. Without oxygen, these buried pieces of organic material are slowly eaten up by bacteria known as anaerobic digesters, which break down what they eat and produce several useful products, like methane gas. For this process to occur, it needs to be quite warm inside the landfill, approximately 40-50 degrees Celsius (approximately 105-120 degrees Fahrenheit). These temperatures are generally quite easily achieved, however, thanks to the heat produced by the many living organisms working to decompose the waste. In fact, many waste management sites employ the use of these digesters in separate large tanks for sewage treatment, in order to capture the large amounts of heat and methane, as well as other by-products that are used to produce fertilizer. When organic materials are mixed with ample air and heat, specialized bacteria growth is quickly encouraged. These bacteria, known as aerobic organisms, help break down the larger compounds containing nitrogen, oxygen, hydrogen and carbon into smaller compounds. These processes are done much quicker than the anaerobic processes mentioned above, and produce on average nineteen times more heat. Landfills generally employ the use of large tractors and other specialized machinery to churn up the waste to achieve this quickened biodegradation. By encouraging oxygen to flow through the mounds, aerobic bacteria are able to remain alive and aerobic biodegradation is facilitated. Most biodegradable materials are able to turn back into nutrient-rich soil, which then can be used for other purposes. At the dump, however, the newly formed soil is generally not re-used, since it is mixed in with other pieces of trash that have not yet or will not decompose. Compost piles are designed for the purpose of re-using soil. They are essentially small dumps in which only organic materials are deposited, and in which aerobic biodegradation is facilitated. As noted before, aerobic biodegradation produces a large amount of heat, so the inside of a compost pile is capable of quite high temperatures. Below is an example of a compost pile. Most of the biodegradation in this experiment will be caused by aerobic organisms, because the trash will be buried quite close to the surface of the soil. Furthermore, the soil compost piles create is great to use for gardening. After the experiment, when the inorganic materials that did not degrade are removed, the soil your class creates can be useful in a classroom garden. Site for the disposal of waste materials by burial. Similar to spoiling, the breaking down of larger molecules into smaller molecules. Remnants of organic materials, often used in gardening. Matter that has come from a recently living organism, is capable of decay, or the product of decay. Matter not having the structure or organization characteristic of living bodies. To decay and become absorbed by the environment. Bury Your Trash! (Be sure to go over the investigating questions from the activity with the class to make sure they understand some of the fundamental concepts imbedded in the activity, before proceeding to the lesson closure). Everyone should take the remnants of garbage from our waste management site and dispose of them in a regular garbage can. Or, if everyone wants, we can move the biodegradable materials to a compost pile if you would like to build one (see lesson extensions). If we put our garbage in the trash, where do you think our experimental pieces may end up? Do any of them have the ability to decay more? It is important for everyone to realize that the trash we create does not just magically disappear. Furthermore, I hope everyone has figured out the difference between biodegradable and non-biodegradable materials. Trash that is biodegradable, and therefore can turn back into soil, does a much better job at maintaining the cycle of nutrients to and from the earth (and our bodies) than does trash that just sits there and does not decay. Ask students to define the term biodegradable. Ask students to explain what a dump is. Ask students to explain what a compost pile is. Ask students to describe what happens to their garbage after it is thrown away. Ask students to identify what types of materials are biodegradable, and what types are not. Bring in a number of new items of trash. Ask students to identify each as biodegradable or not biodegradable. This may be done individually or as a class. A compost pile would complement the concepts covered in this lesson well, giving students a hands-on experience as well. See the below link for simple instructions. http://www.thisland.uiuc.edu/57ways/57ways_31.html 57 Ways - 31. Create a Compost Pile. 1995. University of Illinois Extension. Accessed 4/27/07. http://www.thisland.uiuc.edu/57ways/57ways_31.html Compost. Modified April 23, 2007. Wikipedia. Accessed 4/27/07. http://en.wikipedia.org/wiki/Compost Organic Material. Modified April 16, 2007. Wikipedia. Accessed 4/27/07. http://en.wikipedia.org/wiki/Organic_material Biodegradable. Modified April 23, 2007. Wikipedia. Accessed 4/27/07. http://en.wikipedia.org/wiki/Organic_material