Session 5 - Disposal

Where Does Our Trash Go?
Few of us spend much time pondering the fate of our trash, which helps explain why generate so much of it. Your students will inherit much of our trash along with the challenge of disposing of their own, so they’ll need to know options for waste disposal.


Waste disposal requires difficult civic choices, since no option is perfect.

U.S. Environmental Protection Agency divides trash into seven categories: paper, plastics, metals, glass, yard trimmings, food waste, and other.



Try This!  

Peer inside an incinerator.
Get the lowdown on landfills.
Brush up on recycling.
Dig into the world of composting.
Plan a trashy trip (extension activity).



Inside an Incinerator


Many communities burn their solid waste until nothing remains but fine, white-gray ash, which is they buried in landfills. The energy released by burning trash is sometimes used to generate electricity.

Your students can use this diagram to follow the path of the trash and of the smoke.

Where does the trash go?

  1. A garbage truck dumps its contents into the refuse pit.
  2. The crane lifts trash from the pit into the hopper.
  3. Trash slides down into the primary combustion zone and burns.
  4. A dump truck carries ash to a landfill or other disposal site.


Where does the smoke go?

  1. The acid-gas scrubber removes pollutants from the smoke.
  2. The dust collector gathers, yes, dust particles and adds them to the ash pile for disposal.
  3. A smokestack releases smoke into the air.


The Lowdown on Landfills

Landfills are just what the name suggests—land filled in with trash. The theory, at least for some landfills, was that waste would slowly biodegrade, thereby taking up less space. The reality, however, is that conditions at many landfills preserve trash long after anyone expected—or wanted.

The following links can help your class learn more about landfills:

Indiana’s Monroe County Solid Waste District suggests what we might find in a landfill in 2010.

The Association of Science-Technology Centers provides a primer on landfill anatomy.

National Geographic WORLD , our magazine for kids, explored the subject of landfills in its April 1994 issue.

Dig that Garbage
Excerpted from WORLD, April 1994

Pizza crusts, last week’s newspapers, dead batteries, rotten eggs, old diapers—ewww, gross! But archaeologist William Rathje, of the University of Arizona, in Tucson, really digs this stuff. He dug through layers of garbage in one of the world's largest landfills, in New York City. Dr. Rathje and his students also have carefully sorted through 18,000 trash bags. “I was born to do this,” he says. “My sense of smell isn’t very good.”

His Garbage Project has found that many of our ideas about landfills are...well, rubbish. We may believe that trash in a landfill biodegrades, or breaks down, into a nice natural slop. But Rathje has seen hot dogs that are 40 years old and still look like hot dogs. “Those preservatives really work,” he jokes. He also has found dozens of newspapers that could still be read, even though they were printed in the 1950s.

Biodegradation in a landfill takes place very slowly. The idea of a landfill is to bury the garbage in a pit. Next comes a layer of soil to reduce odors and keep out animals. But much of the garbage is packed so tightly and kept so dry that very little can break down. As a result most landfills may end up preserving garbage instead of helping it rot.


People should recycle and reuse, Rathje says. “But the best way to reduce the amount of stuff we send to landfills is to generate less garbage in the first place.”


What’s in a Landfill?

  • 40 percent—paper, newspaper, and cardboard
  • 20 percent—construction debris
  • 12 percent—plastics
  • 12 percent—yard wastes (grass clippings, leaves, tree branches)
  • 9.8 percent—other
  • 4 percent—food wastes
  • 1.2 percent—disposable diapers
  • Less than one percent—polystyrene foam



Recycling 101

Collecting all those cans, bottles, newspapers, and the rest is only the beginning of recycling. Wisconsin Natural Resources Magazine identified four stages of recycling:

  • collecting recyclable items,
  • separating them by type (before or after collection),
  • processing raw materials into reusable forms, and
  • purchasing and using items made with reprocessed materials.

Two sites may help engage younger students in learning about recycling:




The ABC’s of a Compost Pile

Mother Earth has her own way of recycling. When anything alive dies in the wild, something else eats it. Your students may have heard about scavengers such as jackals and vultures, but do the kids realize that some microbes, fungi, and invertebrates live off the remains of plants and animals?

Savvy gardeners sometimes help Mother Earth along by creating compost piles.

  • A is for assemble: Composters gather and pile scraps from the yard (leaves, twigs, dead flowers, grass, and the like) and the kitchen (fruit rinds, leftover vegetables). No meat, though, since it smells and lures rats.
  • B is for biodegrade: Given enough air, water, and warmth, the material serves as supper for microbes and other organisms.
  • C is for compost: The decaying trash turns into compost, fertilizer sometimes described as “a gardener’s best friend.”

Composting can be a trash collector’s best friend too, since it’s a way of recycling material too moist to incinerate easily. And compost that goes into making the garden bloom is taking up space in a landfill.

Michigan State’s Microbe Zoo site includes an overview of life in a compost pile.



Take a Trashy Trip (extension activity)

If time permits, touring a landfill, dump, or recycling center can make the subject far more real to your students. The Association of Science-Technology Centers offers a screenful of suggestions on arranging a field trip.