Fossil fuels, which include petroleum, natural gas, and coal, supply nearly 90 percent of the energy needs of the United States and other industrialized nations. Because of their high demand, these nonrenewable energy resources are rapidly being consumed. Coal supplies are expected to last about a thousand years.
We must find other sources of energy to meet the increasing fuel demands of modern society. Important alternate sources of energy include: solar, wind, biomass, hydroelectric, geothermal, nuclear, and tidal energy.
One of the benefits of using alternate sources of energy is that many of them are “clean.” This means that they do not cause pollution. Also, many alternative energy sources are renewable energy sources. They are replaced naturally-such as plant life-or are readily available – such as the sun and wind. In addition, the use of renewable forms of energy will allow us to stretch out our current supply of fossil fuels so they will last longer.
In this chapter you will learn how biomass, or organic matter, can be an important energy source. Plants are the most important biomass energy source. Plant material can be burned directly-as with wood-or it can be converted into a fuel by other means. In the experiments that follow you will explore: how water can be heated by composting grass, how a peanut burns, and how corn syrup can be made into ethyl alcohol.
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Materials
- Freshly cut grass clippings
- Cooking thermometer (optional)
- Empty two-liter plastic drink bottle
- Rake
- Water
- Styrofoam cup
Procedure
Ask an adult to help you collect freshly cut grass clippings. You will need enough grass clippings to fill about two large grocery bags. Rake the grass clippings into a pile on a shady spot in the yard. In some parts of the country you will only be able to do this in the spring and summer months when grass grows.
Fill a two-liter plastic bottle with cold water. Starting at the top of the pile dig a hole down into the grass clippings just large enough for the plastic bottle. Place the plastic bottle in the hole, and then fill around it with grass clippings. The top of the plastic bottle should stick out of the pile of grass clippings slightly.
Check the water in the bottle after it has been in the pile of grass clipping for at least twenty-four hours. If you have a cooking thermometer, place it in the bottle for thirty seconds and then read the temperature on the thermometer. If you do not have a cooking thermometer, carefully remove the bottle of water from the pile of grass clippings. Feel the sides of the plastic bottle. CAUTION-THE BOTTLE MAY BE VERY WARM, SO AVOID BURNING YOURSELF. Pour some of the water into a Styrofoam cup and look for water vapor rising from the cup. Place the bottle back into the pile of grass clippings and check it again each day for several days.
Observations
After twenty-four hours in the grass clippings, is the water in the plastic bottle warm when you check it? If you check the water with a thermometer, what is the temperature of the water?
When you pour some of the water into a Styrofoam cup, do you see water vapor rising from the cup?
How many days does the water remain warm?
Does the pile of grass clippings become smaller after a few days? What does the pile of grass clippings look like when the water is no longer warm?
Discussion
The water in the plastic bottle should be warm after the bottle has been in the pile of grass clippings for twenty-four hours. The heat that warms the water comes from the pile of grass clippings, which is decomposing or composting.
The decomposition of dead plant and animal material is nature’s way of recycling important chemical substances. Complex chemical substances in dead plant and animal material are broken down into simple chemical substances during the process. These simpler chemical substances then become nutrients for living plants and soil animals.
Heat is given off during the decomposition process. The more material that is decomposing, the more heat is produced. In this experiment, a large amount of heat is given off by the decomposing grass clippings. This is because you started with a large pile of grass clippings, and grass clippings decompose quickly.
A pile of decomposing grass clippings can reach a temperature of over 71°C (160°F). The water in the bottle may absorb enough heat from the decomposing grass to reach a temperature as high as 60°C (140°F) after a day or two. For comparison, most household hot water heaters are set to deliver hot water with a temperature between 54°C (130°F) and 71°C (160°F).
Other Things to Try
How much water can you heat with composting grass clippings? To find out, repeat this experiment with a one-gallon plastic milk jug filled with water. Does the water in the jug become warm?
Repeat this experiment, but remove the bottle of water from the pile of grass clippings after twenty-four hours. Fill a second two-liter plastic bottle with cold water from a sink faucet and place it into the pile of grass clippings. Does the water in this bottle become warm after a couple of hours?
Is there a minimum amount of grass clippings that are needed to make enough heat to heat the water in a two-liter plastic bottle? To find out, surround a two-liter plastic bottle filled with water with just enough grass clippings to cover it. Does the water become warm after twenty-four hours?
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Microorganisms break down plant and animal matter through exothermic chemical reactions. In other words, the chemical reactions give off heat.
What is causing the heat in the decomposing process?
wow so cool! thanks for sharing.