The art of composting has been part of our global culture since ancient times. The basic principles are quite simple, and adhering to them will result in an efficient and successful outcome. Studies have shown that home composting can divert an average of 700 lbs. of material per household per year from the waste stream. Municipal composting carries a greater environmental cost, but not nearly as high as if leaf and yard waste are disposed of by conventional means. Composting is an excellent way to avoid both wasting useful, natural resources and creating environmental problems, while at the same time producing a high quality and inexpensive soil amendment.

Composting is the transformation of organic material (plant matter) through decomposition into a soil-like material called compost. Invertebrates (insects and earthworms), and microorganisms (bacteria and fungi) help in transforming the material into compost. Composting is a natural form of recycling, which continually occurs in nature.

An ancient practice, composting is mentioned in the Bible several times and can be traced to Marcus Cato, a farmer and scientist who lived in Rome 2,000 years ago. Cato viewed compost as the fundamental soil enhancer, essential for maintaining fertile and productive agricultural land. He stated that all food and animal wastes should be composted before being added to the soil. By the 19th century in America, most farmers and agricultural writers knew about composting.

Today there are several different reasons why composting remains an invaluable practice. Yard and food wastes make up approximately 30% of the waste stream in the United States. Composting most of these waste streams would reduce the amount of Municipal Solid Waste (MSW) requiring disposal by almost one fourth, while at the same time provide a nutrient-rich soil amendment. Compost added to gardens improves soil structure, texture, aeration, and water retention. When mixed with compost, clay soils are lightened, and sandy soils retain water better. Mixing compost with soil also contributes to erosion control, soil fertility, proper pH balance, and healthy root development in plants.

The standard means of disposal for most yard and food waste include landfilling and incineration. These practices are not as environmentally or economically sound as composting. Yard waste which is landfilled breaks down very slowly due to the lack of oxygen. As it decomposes, it produces methane gas and acidic leachate, which are both environmental problems

Landfilling organic wastes also takes up landfill space needed for other wastes. Incinerating moist organic waste is inefficient and results in poor combustion, which disrupts the energy generation of the facility and increases the pollutants that need to be removed by the pollution-control devices. Composting these wastes is a more effective and usually less expensive means of managing organic wastes. It can be done successfully on either a large or small scale, but the technique and equipment used differ.

Decomposition

Decomposition occurs naturally anywhere plants grow. When a plant dies, its remains are attacked by microorganisms and invertebrates in the soil, and it is decomposed to humus. This is how nutrients are recycled in an ecosystem. This natural decomposition can be encouraged by creating ideal conditions. The microorganisms and invertebrates fundamental to the composting process require oxygen and water to successfully decompose the material. The end products of the process are soil-enriching compost, carbon dioxide, water, and heat.

Composting is a dynamic process which will occur quickly or slowly, depending on the process used and the skill with which it is executed. A neglected pile of organic waste will inevitably decompose, but slowly. This has been referred to as "passive composting," because little maintenance is performed. Fast or "active" composting can be completed in two to six weeks. This method requires three key activities; 1) "aeration," by turning the compost pile, 2) moisture, and 3) the proper carbon to nitrogen (C:N) ratio. Attention to these elements will raise the temperature to around 130=-140=, and ensure rapid decomposition.

The success with which the organic substances are composted depends on the organic material and the decomposer organisms involved. Some organic materials are broken down more easily than others. Different decomposers thrive on different materials as well as at different temperature ranges. Some microbes require oxygen, and others do not; those that require oxygen are preferable for composting.

A more diverse microbial community makes for a more efficient composting process. If the environment in the compost pile becomes inhospitable to a particular type of decomposer, it will die, become dormant, or move to a different part of the compost pile. The transforming conditions of the compost pile create a continually evolving ecosystem inside the pile.

Factors Affecting The Composting Process

All organic material will eventually decompose. The speed at which it decomposes depends on these factors:

1. carbon to nitrogen ratio of the material
2. amount of surface area exposed
3. aeration, or oxygen in the pile
4. moisture
5. temperatures reached in compost pile
6. outside temperatures

Carbon-to-Nitrogen Ratios

Carbon and nitrogen are the two fundamental elements in composting, and their ratio (C:N) is significant. The bacteria and fungi in compost digest or "oxidize" carbon as an energy source and ingest nitrogen for protein synthesis. Carbon can be considered the "food" and nitrogen the digestive enzymes.

The bulk of the organic matter should be carbon with just enough nitrogen to aid the decomposition process. The ratio should be roughly 30 parts carbon to 1 part nitrogen (30:1) by weight. Adding 3-4 pounds of nitrogen material for every 100 pounds of carbon should be satisfactory for efficient and rapid composting. The composting process slows if there is not enough nitrogen, and too much nitrogen may cause the generation of ammonia gas which can create unpleasant odors. Leaves are a good source of carbon; fresh grass, manures and blood meal are sources of nitrogen.

Surface Area

Decomposition by microorganisms in the compost pile takes place when the particle surfaces are in contact with air. Increasing the surface area of the material to be composted can be done by chopping, shredding, mowing, or breaking up the material. The increased surface area means that the microorganisms are able to digest more material, multiply more quickly, and generate more heat. It is not necessary to increase the surface area when composting, but doing so speeds up the process. Insects and earthworms also break down materials into smaller particles that bacteria and fungi can digest.

Aeration

The decomposition occurring in the compost pile takes up all the available oxygen. Aeration is the replacement of oxygen to the center of the compost pile where it is lacking. Efficient decomposition can only occur if sufficient oxygen is present. This is called aerobic decomposition. It can happen naturally by wind, or when air warmed by the compost process rises through the pile and causes fresh air to be drawn in from the surroundings. Composting systems or structures should incorporate adequate ventilation.

Turning the compost pile is an effective means of adding oxygen and brings newly added material into contact with microbes. It can be done with a pitchfork or a shovel, or a special tool called an "aerator," designed specifically for that purpose. If the compost pile is not aerated, it may produce an odor symptomatic of anaerobic decomposition.

Moisture

Microorganisms can only use organic molecules if they are dissolved in water, so the compost pile should have a moisture content of 40-60 percent. If the moisture content falls below 40 percent the microbial activity will slow down or become dormant. If the moisture content exceeds 60 percent, aeration is hindered, nutrients are leached out, decomposition slows, and the odor from anaerobic decomposition is emitted. The "squeeze test" is a good way to determine the moisture content of the composting materials. Squeezing a handful of material should have the moisture content of a well wrung sponge. A pile that is too wet can be turned or can be corrected by adding dry materials.

Temperature

Microorganisms generate heat as they decompose organic material. A compost pile with temperatures between 90= and 140=F (32=-60=C) is composting efficiently. Temperatures higher than 140=F (60=C) inhibit the activity of many of the most important and active organisms in the pile. Given the high temperatures required for rapid composting, the process will inevitably slow during the winter months in cold climates. Compost piles often steam in cold weather. Some microorganisms like cool temperatures and will continue the decomposition process, though at a slower pace.

Backyard composting can be done using a variety of different systems, enclosures, or containers. Composting systems or bins can be constructed at home or purchased commercially. Depending on where you live, youmay have a problem with rodents if vegetative food wastes are combined with yard wastes. If so, an enclosed space or bin is advisable. The methods employed will vary somewhat depending on the system you choose, but the principles and purpose remain the same. This is true for large-scale composting projects as well.

Some municipalities collect yard waste at the curbside similar to the way recyclables are collected. It is taken to a central location and formed into windrows, triangular-shaped rows from 5 to 8 feet high and as long as necessary. Turning for aeration is done about once a month using a front-end loader or other type of heavy equipment made specifically for that purpose. The temperature and moisture are checked twice a week. The finished compost may be sold, given away, or used by the municipality in public works projects. Backyard composting eliminates the environmental and economic costs of the heavy equipment used to bring yard waste to a composting site and turn the windrows.

  Food Wastes: Vermicomposting and Food Digestors

Vermicomposting or worm composting is the easiest way to recycle food wastes and is ideal for people who do not have an outdoor compost pile. Composting with worms avoids the needless disposal of vegetative food wastes and enjoy the benefits of a high quality compost. It is done with "redworms" (Eisenia foetida) who are happiest at temperatures between 50= and 70= F and can be kept indoors at home, school, or the office. As with outdoor composting, it is best to avoid putting bones, meats, fish, or oily fats in the worm box as they emit odors and may attract mice and rats. When cared for properly, worms process food quickly and transform food wastes into nutrient-rich "castings." Worm castings are an excellent fertilizer additive for gardens or potted plants.

The redworms are placed in a box or bin which can be built or purchased, along with "bedding" of shredded cardboard and/or paper moistened to about 75% water content. The container should be wide enough so that food scraps can be buried in a different location each time. The dimensions of the container and the amount of worms required initially will depend on how much organic food waste will need to be composted each week.

The worms will gradually reproduce or die according to the amount of food they receive. A sudden addition of a large amount of food waste may attract fruit flies, so increases should be made gradually. In a healthy box, worms can build large populations and consume four to six pounds of food scraps per week. About four to six months after the box has been started, the worms will have converted all of the bedding and most of the food waste into "castings" which will need to be harvested so the process can begin again.

Food waste digestors are an option for people who want to reduce the amount of food waste they produce but do not have a compost pile. These units resemble commercially produced compost bins, but differ in purpose. They are designed to accept food wastes otherwise inappropriate for composting such as meats, fish, fats, or oily food scraps. In general they are built to prevent odors from being released and prevent rodents from entering the unit. Food waste digestors are fundamentally different from worm boxes and compost piles, because the digestors do not ultimately produce a soil enhancing product. Their purpose is to cut down on the volume of food waste generated. Food waste digestors are not a "magic hole in the ground" however, and the decomposed food residue must periodically be emptied into the trash.