Composting/Landfills

From Experiment Central, published by U·X·L

Composting is the process in which organic wastes are broken down biologically and become dark, fertile soil called humus. An ancient practice, composting probably began when the original hunter-gatherers began cultivating food and saw that crops grew better in areas where the soil contained manure, the waste matter of animals.

Agricultural composting with manure was being used in the Mesopotamia Valley in Asia as early as 13 B.C. Not surprisingly, Native American tribes practiced composting long ago, as did the first colonists who arrived in North America.

A smelly solution

French chemist Jean Baptiste Boussingault (1802-1887) made significant contributions to agricultural chemistry by suggesting that good soil was made by the action of microorganisms, bacteria, and fungi that break down waste. Working on his farm, he applied and studied the results of organic methods of farming from 1834 to 1876.

At that time, composting used mostly animal manure or dead fish, as well as nutrient-rich muck from swampy areas. By the twentieth century, large animals such as the buffalo, whose droppings fertilized the prairie soil, were disappearing as were many of the farming communities that contributed barnyard manure to compost piles.

In 1934, Sir Albert Howard, an Englishman, developed the modern organic concept of farming. Through several years of research in Indore, India, he formulated the Indore method, a process that used three times more plant waste than manure in sandwich-like layers of green or wet material. Howard also pointed out the importance of microorganisms in the process. In 1942, J.I. Rodale began publishing Organic Farming and Gardening. Rodale used Howard's techniques and experimented with his own. He is considered the pioneer of organic methods of farming in the United States.

Chomping microbes

How does composting work? Let us begin with the basics, the organic waste. That would be vegetable scraps such as carrot tops and peelings, plus leaves, paper bags, grass clippings, tea bags, and coffee grounds. Carbon in these organic waste materials provides food for the microorganisms, starting the composting process. When these microbes chomp away and begin digesting, the carbon is burned off or oxidized, causing the composting pile to heat up. The heat kills any harmful organisms. Macroorganisms—such as earthworms, insects, mites, and grubs—continue the composting process by chewing the organic matter into smaller pieces. Through digestion and excretion, both types of organisms release important chemicals into the compost mass, which then becomes humus, a nutrient-rich soil.

The transformation is speeded up by a balanced supply of carbon and nitrogen, the oxygen required by the microorganisms, enough moisture to allow biological activity, and suitable temperatures. But it is really the diverse microorganisms that chomp away and activate the process. Without them, we would be buried in wastes.

In the United States, more garbage is generated than in any other country in the world. Materials that could be used in composting make up 20 to 30 percent of the waste stream—the waste output of any area or facility. This figure doubles in the autumn when leaves and garden clippings are added. All this waste winds up in landfills.

Landfills that raised the roof

Landfills are huge depressions in the ground or equally huge mounds above ground where garbage is dumped. Like compost piles, landfills also have centuries-old beginnings. The ancient cities of the Middle East were built up over time on mounds that contained the remains of everyday life. In excavations of the ancient city of Troy, in what is now Greece, building floors were found to have layers of animal bones and artifacts that had been alternated with layers of clay. These layers piled up until it was necessary to raise roofs and rebuild doorways.

During the Bronze Age (3000-1000 B.C.), the city of Troy rose about 4.7 feet (1.4 meters) each century (100 years) because of these accumulations. Landfilling has also been used to extend shorelines. In New York City during the eighteenth century, shorefront roads were extended into the water by landfill that included broken dishes, old shoes, and even the rotted hulls of boats.

Sanitary landfills

In the 1930s, solid waste materials covered with soil became known as "sanitary landfill." As with composting, a decomposition process takes place in landfills. The process has an aerobic and an anaerobic phase. Aerobic means requiring oxygen. Anaerobic means functioning without oxygen. In the aerobic phase, biodegradable solid wastes react with the landfill's oxygen to form carbon dioxide and water. The landfill temperature rises and a weak acid forms within the water, dissolving some of the minerals. Microorganisms that do not need oxygen break down wastes into hydrogen, ammonia, carbon dioxide, and inorganic acids during the anaerobic stage. Gas in the form of carbon monoxide and methane is produced in the third stage of decomposition.

In a landfill, many of the materials, such as plastic, glass, and aluminum cans, containers, and bottles, can take up to forty years or more to decompose. As a result, these materials are quickly filling the space available in landfills. That is why recycling is encouraged in most communities. In recycling, waste materials are used to produce new materials.

In the United States, about 80 percent of the garbage is dumped into landfills. Landfills are not bottomless pits. Soon half of all U.S. landfills will be full. In New York State, for example, all landfills will be officially closed by the end of 2000. Only Fresh Kills, the largest sanitary landfill in the world, still operates, receiving more than 200 tons (180 metric tons) of waste a day. Understanding how composting and landfills work helps everyone become more aware of what happens to the garbage that is thrown away.

Composting: Using organic material to grow plants

Purpose/Hypothesis

This experiment will examine the principle of composting, the process of converting complex organic matter into the basic nutrients needed by living organisms. This experiment will utilize organic waste (household and yard waste) as nutrients for plants. It will allow you to investigate which waste products can be composted and best utilized by plants. Before you begin, make an educated guess about the outcome of the experiment based on your knowledge of composting and decomposition. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:

• the topic of the experiment
• the variable you will change
• the variable you will measure
• what you expect to happen

A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "Yard waste will break down faster than household waste and will provide more nutrients for plants."

In this case, the variable you will change is the type of waste used to make compost, either yard waste or household waste, and the variable you will measure is the amount of decomposition of the waste and the growth of the plants. You expect the yard waste to break down faster and produce taller plants. As a control experiment, you will grow one plant without any waste to judge the growth without compost. If the plant with yard waste compost grows taller than either of the other two plants, and the yard waste has decomposed more than the household waste, your hypothesis will be supported.

Level of Difficulty

Moderate, because of the time involved.

Materials Needed

• Three 2-gallon (7.5-liter) potting containers (terra cotta, ceramic, or plastic) with one or more holes in the bottom for drainage
• 3 pounds (1.3 kilograms) topsoil
• 3 to 5 pounds (1.3 to 2.3 kilograms) sand
• 3 to 5 pounds. (1.3 to 2.3 kilograms) organic waste (Use two types: household—table scraps, rotten vegetables, coffee grounds, etc.—and yard waste—leaves, twigs, grass clippings, weeds, etc.)
• 3 small identical living plants (annual flowers or vegetable plants), such as sunflowers, beans, or tomatoes
• 3 stakes for markers (Popsicle sticks will work)
• plastic or rubber gloves

Approximate Budget

$5 (use topsoil from your yard if available).

Timetable

Two to four months.

How to Experiment Safely

Wear gloves when handling waste and mixing soil.

Step-by-Step Instructions

1. Mix the topsoil and sand together to create the soil base.
2. Prepare the control experiment. Fill pot #1 with the soil base, leaving 2 inches (5 centimeters) at the top of the pot. Place one plant into the soil, covering all the roots. Water generously.
3. Prepare pot #2. Add to the soil base the household waste you collected (scraps, rotten vegetables, etc.). Mix the soil thoroughly. Place a plant into the soil, covering all the roots. Water generously.
4. Prepare pot #3. Follow the directions for pot #2 but substitute the yard waste (grass clippings, leaves, etc.) instead of household waste.
5. Put markers in the pots identifying them as "control," "household," or "yard." Place the pots in a sunny location and monitor the growth of the plants. If possible, take photographs of them at the beginning of the experiment. Water the plants when the soil feels dry. Do not allow them to dry out completely.
6. Graph the weekly growth of the plants, recording the plant height, number of leaves, and root development, if visible.
7. After 2 to 4 months record the final heights and differences in the plant growth between each pot. Empty the pots and evaluate the amount of composting that occurred in the soil. Look for recognizable waste materials, record results.

Summary of Results

During the experiment you will be recording the plant growth in the three pots. Ideally, the pot that is composting fastest will provide the most nutrients for its plant. It is essential to measure the height of each plant. You may also want to record which plant flowered first, how often it bloomed, and whether it produced fruit.