Activity 1b: Traditional Composting

Background

As you studied ecological niches, you looked at decomposer organisms. There are macroorganisms and microorganisms that speed the decay process, but by far the microorganisms are the most effective. Traditional composting relies on the activity of microorganisms to break down wastes. There are a variety of ways of classifying microorganisms. We will look at two of these in relationship to composting microorganisms.

The first classification deals with whether or not the organism requires oxygen to carry out its work. Aerobic bacteria require oxygen and anaerobic bacteria do not. Aerobic bacteria are the most important decomposers. They obtain energy by oxidizing organic material and in doing so produce heat. Anaerobic bacteria can also break down waste materials, but they are much slower and produce numerous byproducts that smell bad such as hydrogen sulfide, cadaverine, and putrescine. Most of these byproducts are not useful to plant growth.

Another classification system deals with the temperatures at which the organisms can live and work. The three types are psycrophilic, mesophilic, and thermophilic. Psycrophilic bacteria work in the lowest temperature ranges. They are most active at about 55°F. The mesophilic bacteria work in moderate temperatures from 70°F to 100°F. The thermophilic bacteria thrive at temperatures above 100°F. As a compost pile is built and heats up the population of bacteria that is active changes. The thermophilic bacteria are the most efficient decomposers.

Other microorganisms that work as decomposers include the actinomycetes a higher form of bacteria and fungi. They help to break down the more resistant materials in the pile such as lignin and cellulose. Both of these organisms work better in moderate temperature.

Equipment

  • Containment material or composter
  • Waste Carbon sources (brown stuff)
  • Waste Nitrogen sources (green stuff)
  • Garden hose with spray nozzle
  • Pitchfork or shovel
  • Work gloves

Safety Precautions

  • Wear work gloves when working with compost
  • Tell your teacher if you have any environmental allergies
  • Wash your hands with soap and water after working with the compost

Procedure

Setting Up the Compost Pile

  1. Build or set up the containment area. The area should be at least 3 feet by 3 feet by 3 feet. Follow your teacher’s instructions for the materials that you have on hand.
  2. Gather and separate carbon and nitrogen sources. You will need 25-35 garbage bags of waste materials.
  3. Connect garden hose and have water available to building site. You will use lots of water in building the pile so you will want to wear shoes that can get wet.
  4. Put about a 6 inch layer of loose brown material in the bottom of your compost area. Wet it down thoroughly with the hose.
  5. Put a layer of green stuff on top of the brown stuff, and water it thoroughly.
  6. Continue to layer brown and green stuff, watering each layer as it is added and lightly packing the layers to ensure good contact between the layers.
  7. Top your pile with about 6 inches of brown stuff. Wet pile thoroughly.

Observing the Compost Pile

  1. Use a compost thermometer or other means to take an initial temperature reading from the center of the pile. The temperature should be above ambient air temperature. Record the temperature in a log. If the temperature has not risen above ambient temperature, be sure the pile is wet and tamp down (compact) and give it another 24 hours to heat up. If it still has not heated up look at the trouble shooting guide for suggestions.
  2. In your small group determine what information should be collected for the compost pile and develop a log sheet. Then as a class compare data sheets and come to a consensus on a final version.
  3. Develop a schedule for observing and maintaining the pile and assign tasks to individuals. If for some reason you are unable to fulfill your assignment, make arrangements for one of your lab partners to take your place.
  4. Make other observations of the pile in the log: What did it look like, smell like, etc.? Did it look like it had been disturbed by animals? Were there insects, worms, slugs, snails or other macro decomposers present?
  5. Make observations of the pile including temperature every day or every few days as directed by your teacher. Let your teacher know if there are any problems with the pile such as bad odors, pests, and so forth.

Turning the Compost Pile

  1. After the pile heats up, the temperature will begin to decrease. When this happens after several days to a week, you will know that it is time to turn your pile.
  2. Use the method of turning your pile appropriate to the style bin you have. Your teacher will help you determine the method.
  3. As you turn the materials in the bin, ensure that they are still moist and add more water as needed to keep the compost moist (comparable to a wrung out sponge).
  4. Once your pile has been turned, continue taking regular temperature readings. You should notice the pile heat back up. Continue watching until you see that it is cooling back down and repeat the turning process.
  5. Generally, turning the pile once a week for the first few weeks and then less frequently is sufficient.

Clean-up

  1. Clean tools off after each use and store in proper place.
  2. Roll up garden hose and store to prevent tripping hazard.
  3. Dispose of trash bags that the raw materials came in properly.
  4. Clean up any blowing debris from your pile and keep it within the confines of the bin.
  5. When compost is finished, use it as decided with your teacher.
  6. Deconstruct bin if it will no longer be used and store as instructed by your teacher.

Observations and Data Collection

  1. List and describe the materials you added to your compost pile. Classify them as a nitrogen source or carbon source.
  2. Describe the changes you observed in your pile each week.
  3. Discuss the reasons for turning a compost pile.
  4. Describe any problems you encountered with your compost pile and what steps you took to correct those problems.
  5. Plot the temperature of the pile over time and indicate major events such as when the pile was turned, materials added and so forth. Describe why you think the temperature fluctuated as it did.
  6. When your teacher tells you, make final observations of the pile. Is the composting process complete? What does it look like? What changes have occurred? How can you use the finished material?

Challenge

  1. If you were repeating your composting experiment, what changes would you try to increase the efficiency of your process?
  2. Describe an experiment to determine which type of composting process, batch or continuous, would produce the most compost in a year.
  3. Assess the feasibility of traditional composting for your home’s organic wastes.

Activity 1b: Traditional Composting
Page 1 of 3 / Contextual Biology Integrated Projects
Created by the Center for Occupational Research and Development