Composting Process
Composting Process
Compost contains both carbon and nitrogen sources, which can be simplified as browns for carbon (e.g., leaves, straw, woody materials) and greens for nitrogen (e.g., grass and food scraps). Adequate sources of carbon and nitrogen are important for microorganism growth and energy. The ideal ratio is 30 parts brown to 1 part green. Odor and other problems can occur if the ratio or any of the factors discussed below are not in the correct balance.
The decomposition of organic materials in composting involves both physical and chemical processes. During decomposition, organic materials are broken down through the activities and appetites of various invertebrates that will naturally appear in compost, such as mites, millipedes, beetles, sowbugs, earwigs, earthworms, slugs, and snails. These microorganisms need adequate moisture and oxygen to degrade the organic materials in the most efficient manner.
Microbes in the pile create considerable heat and essentially "cook" the compost. Temperatures between 90 and 140 degrees Fahrenheit are common in properly maintained compost piles, but may not reach these levels in backyard compost piles. These high temperatures are necessary for rapid composting as well as for destroying weed seeds, insect larvae, and potentially harmful bacteria. When the compost is finished, it has a crumbly texture throughout the pile.
- Red wigglers (i.e., the worms used in vermicomposting) eat their weight in organic matter each day.
- More than 67 percent of the municipal solid waste produced in the United States (including paper) is compostable material.
- There are more than 3,800 yard trimmings composting facilities nationwide.
- MSW Facts and Figures provides additional information such as the number of states with yard waste bans.
Whether composting occurs in the backyard, at a community site with yard trimmings, or in an industrial facility, the resulting compost is a valuable product. Not only can compost be used as a soil additive for backyard gardens and farm lands or to beautify highways and other landscaping projects, but it also has many innovative uses. Below is a list of different composting programs. For a complete list of composting definitions, view EPA's report entitled Organic Materials Management Strategies.
- Backyard composting. Hundreds of thousands of individuals across the country compost in their own backyards, typically in a fenced off area or bin. Backyard composting provides a convenient way to reduce the volume of trash a household produces. It also provides a valuable product that can enhance the soil and increase the growth and health of the yard.
- Yard trimmings composting. Composting also occurs on a large scale, operated by private sector firms or community public works departments. At these sites, the compostable material is taken to a central location. There, it is typically processed in aerated windrows, where organics are formed into rows or long piles. Some sites will add compostable MSW into the mix to keep items out of the landfill. The finished compost can be sold, given away, or used by the company or municipality in local landscaping projects.
- Mixed MSW composting. Composting of mixed municipal solid waste is another option. This generally occurs at a medium-to-large scale facility, operated by private sector firms or community public works departments. Generally, mixed MSW is received at the site. Recyclables such as glass and aluminum, and non-compostables are removed early in the process. The remaining organic material is composted, generally using aerated windrows. In-vessel composting, where the material is left to decompose while enclosed in a temperature and moisture controlled chamber, is another possibility. Final screening steps remove any remaining plastic film and similar contents. The finished compost can be sold, given away, or used by the company or municipality in local landscaping projects.
- Vermicomposting. Although not significant in terms of waste diversion, vermicomposting is being used in some places and is popular in classrooms as a teaching tool. This method of composting uses a container of food scraps and a special kind of earthworm known as a red wiggler. Over time, the food is replaced with worm droppings, a rich brown matter that serves as an excellent natural plant food. Vermicomposting requires less space than normal composting methods, and is, therefore, ideal for classrooms, apartments, and other settings in high-density urban areas.
Source - U.S. Environmental Protection Agency
