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How Composting Works


Composting Biology

Composting creates the ideal conditions for the natural decay or rotting processes that occur in nature. Composting requires the following:

  • Organic waste - newspaper, leaves, grass, kitchen waste (fruits, vegetables), woody materials
  • Soil - source of microorganisms
  • Water
  • Air - source of oxygen

The compost process

During composting, microorganisms from the soil eat the organic (carbon containing) waste and break it down into its simplest parts. This produces a fiber-rich, carbon-containing humus with inorganic nutrients like nitrogen, phosphorus and potassium. The microorganisms break the material down through aerobic respiration, and require oxygen that they get from the air you introduce when you turn the material in the compost bin. The microorganisms also require water to live and multiply. Through the respiration process, the microorganisms give off carbon dioxide and heat -- temperatures within compost piles can rise as high as 100 to 150 degrees Fahrenheit (38 to 66 C). If the compost pile or bin is actively managed by turning and watering it regularly, the process of decomposing into finished compost can happen in as little as two to three weeks (otherwise, it may take months).

The compost conditions must be balanced for efficient decomposition. There must be:

  • Plenty of air - mixture should be turned daily or every other day
  • Adequate water - mixture should be moist, but not soaking wet
  • Proper mix of carbon to nitrogen - ratio should be about 30:1 (see Elements of Composting: C:N ratio and Virtual Pile for details)
  • Small particle size - big pieces should be broken up, as smaller particles break down more rapidly
  • Adequate amount of soil - should provide enough microorganisms for the process
Why Compost?
The major goal of composting is to reduce the amount of solid waste you generate. If you reduce solid waste, you will save space in municipal landfills, which will ultimately save you tax money. Finished compost has the advantage of being a useful natural fertilizer that is more environmentally friendly than synthetic fertilizers.

The compost pile actually has a complex organization of living organisms -- a foodweb. Bacteria and fungi primarily break down the organic matter in the trash. Single-celled organisms (protozoa), small worms (nematodes), and mites feed on the bacteria and fungi. Predatory nematodes, predatory mites and other invertebrates (sowbugs, millipedes, beetles) feed on the protozoa, mites and nematodes. All of these organisms work to balance the population of organisms within the compost, which increases the efficiency of the entire process.


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