Compost Columns Lab
Where do things go when they die?
Explore the process of decay or decomposition (the break down of
wastes—Ex: food going bad after being left too long in the
refrigerator).
Introduction
Composting is based on the biological process of decomposition. What turns
plants and animals into compost? Microscopic bacteria and fungi, which feed on
dead tissue, are the chief agents.
What affects the composting process? The amount of moisture and air,
temperature, light, sources of bacteria and fungi, and the nature of the
decomposing material are all critical. The presence or absence of air (oxygen) is
one of the most important factors in composting. The practice of composting
allows air and moisture to speed the natural process of biodegradation. Making a
compost column lets you see and experiment with this process, and witness nature’s
world of recycling. The decay of biomass produces matter in the form of small
molecules.
Materials:
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Three clear, plastic, 2-liter soda bottles with caps - cleaned, with the labels removed
Window screen - 2-inch by 2-inch (5-cm by 5-cm) square piece (hardware stores may have
scrap pieces this size)
Piece of wire - 6 inches (15 cm) long; picture frame wire or electrical wire works well
(hardware stores may have scrap pieces available)
Small nail, skewer or dissecting needle
Clear, plastic packing tape
Coffee filter - basket type
Pair of pantyhose
Scissors
Newspaper
Soil
Trash to be composted
Assembling the compost column from pieces of 2-liter soda
bottles (top left):
Window screen is wrapped around Bottle 3 (top right);
Air holes are poked into Bottles 2 and 3 with a needle
(bottom left, bottom right).
A. To assemble the compost column, do the following:
1. Use the scissors to cut the three bottles as shown above. Cut Bottle 1 in
half and trim the top portion just below the curve. Cut the top and bottom
of Bottle 2 along the curved portions. Cut the bottom off Bottle 3 along the
curved portion.
2. Take Bottle 3, wrap the window screen over the mouth of the bottle and
fasten it below the neck with the wire, as shown above.
3. With the nail, skewer or needle, poke many air holes in the sides of Bottle 2
and 3, as shown above.
4. Place Bottle 3 upside down in the bottom half that was cut from Bottle 1, as
shown below, and fasten it with tape. You may want to use a few pieces of
tape that you can remove periodically to drain the water that will collect in
the bottom half.
5. Place Bottle 2 inside Bottle 3, as shown below, and fasten it with tape.
6. Take the top piece from Bottle 1, with its cap, and use it to cover the open
end of Bottle 2. This will be the cap of the finished compost column, as
shown below.
Stacking the pieces of the compost column
(tape has been omitted for clarity)
B. To load the compost column, do the following:
1. Place the coffee filter snugly in the bottom of Bottle 2 so that it sits just
above the opening. The coffee filter acts as a pre-filter to keep the screen
from becoming clogged with soil particles.
Coffee filter used as a pre-filter
2. On a sheet of newspaper, mix the soil and trash to be composted. You can
experiment with the amounts of soil and trash used.
3. Fill the compost column with the soil/trash mixture.
4. Cap the compost column. Fasten the cap with tape.
5. Add water to the column through the top-bottle cap. You can measure the
amount of water if you wish, and see how much works best. Water will
percolate down through the soil/trash mixture and collect in the bottom.
You will have to drain the bottom periodically.
6. Cut one of the legs in the pantyhose, turn it upside down and cover the
compost column with it. The pantyhose cover is effective in keeping fruit
flies and gnats from moving in and out of the column.
You will have to continually add water and drain the bottom, either daily or every
other day. You can turn the compost if you want to, but you can also leave it as is -the air holes in the side should provide sufficient aeration.
Here are some experiments that you can do with your column:
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Weigh the column daily and graph the change in weight as the compost
develops.
Monitor and graph the amount of water used by the column daily. Do this by
subtracting the volume of water collected at the bottom from the volume of
water you've added to the top.
Measure the temperature of the column with a soil thermometer daily and
graph it.
Take notes about the appearance of the trash in the column daily. How long
does it take to decompose?
Collect the drainage water and look at it under a microscope to see the
microscopic organisms that live in the compost.
http://home.howstuffworks.com/composting3.htm
Special Note for Teacher:
Mold and other evidence of decomposition may appear within the first few days
after creating your compost heap. In two or three months, soft organic
material such as leaves, fruits, vegetables, and grain products will decompose
dramatically.
Moisture: It is important to keep the compost heap moist in order to observe
more rapid decomposition. Avoid adding too much water to the heap or it will
become waterlogged. This can create an anaerobic environment. An anaerobic
environment is one that completely lacks oxygen. It is this kind of environment
that will create nasty odors.
Odor: Odor is a by- product of decay or decomposition. Odors may be strong
at first, but will mellow after some time. The strongest odors come from
animal products such as meat and dairy products. Grapefruit rinds and grass
cuttings can also produce strong odors. If you use food scraps, mix in leaves,
twigs, and dried grass to reduce odors. Also, putting a layer of soil on top of
contents lessens the odor.