Composting is a form of recycling.  The composting of yard trimmings and municipal solid waste can help decrease the amount of solid waste that must be sent to a landfill or combustor, thereby reducing disposal costs.  At the same time, composting yields a valuable product that can be used by farmers, landscapers, horticulturists, government agencies, and property owners as a soil amendment or mulch.

The compost product enhances the condition of soil, reduces erosion, and help suppress plant diseases. Several factors determine the chemical environment for composting, especially:

(a) the presence of an adequate carbon (food)/energy source,

(b) a balanced amount of sufficient nutrients,

(c) the correct amount of water,

(d) adequate oxygen,

(e) appropriate pH, and

(f) the absence of toxic constituents that could inhibit microbial activity.

Municipal solid wastes contain up to 70 percent by weight of organic materials.  Yard trimmings, which constitute 20 percent of the MSW stream, may contain even larger proportions of organic materials. In addition, certain industrial by-products—those from the food processing, agricultural, and paper industries—are mostly composed of organic materials. Composting organic materials, therefore, can significantly reduce waste stream volume.

Diverting such materials from the waste stream frees up landfill space needed for materials that cannot be composted or otherwise diverted from the waste stream.

Composting owes its current popularity to several factors, including increased
landfill tipping fees, shortage of landfill capacity, and increasingly restrictive
measures imposed by regulatory agencies. In addition, composting is
indirectly encouraged by states with recycling mandates that include composting as an acceptable strategy for achieving mandated goals, some of which reach 50-60 percent. Consequently, the number of existing or planned composting programs and facilities has increased significantly in recent years.

Composting may also offer an attractive economic advantage for communities
in which the costs of using other options are high. Composting is
frequently considered a viable option only when the compost can be marketed—that is, either sold or given away. In some cases, however, the benefits of reducing disposal needs through composting may be adequate to justify choosing this option even if the compost is used for landfill cover.

Composts, because of their high organic matter content, make a valuable
soil amendment and are used to provide nutrients for plants. When mixed into
the soil, compost promotes proper balance between air and water in the resulting mixture, helps reduce soil erosion, and serves as a slow-release fertilizer.

Up to 70 percent of the Municipal Solid Waste (MSW) waste stream is organic material. Yard trimmings alone constitute 20 percent of MSW. Composting organic materials can significantly reduce waste stream volume and offers economic advantages for communities when the costs of other options are high.

Because the water content of most feedstocks is not adequate, water is usually added to achieve the desired rate of composting. A moisture content of 50 to 60 percent of total weight is ideal. Excessive moisture can create anaerobic conditions, which may lead to rotting and obnoxious odors. Adding moisture may be necessary to keep the composting process performing at its peak. Evaporation from compost piles can also be minimized by controlling the size of piles.