As the field of solid waste management becomes more developed and specialized, the categories into which solid waste is sorted and managed become more numerous. Yard waste—often called vegetative waste—includes leaves, grass clippings, tree trimmings, and other plant materials that are typically generated in outdoor residential settings. Depending on the season and the neighborhood, leaves may account for 5–30% of the total municipal solid waste stream, grass clippings may comprise 10–20%, and wood may form about 5–10%. Yard waste does not include food and animal wastes except possibly as impurities. Yard waste is usually perceived as cleanest type of solid waste, in contrast to household refuse or industrial and commercial trash.
Since yard waste is almost entirely vegetative in nature, it lends itself easily to composting . Composting is the natural breakdown of organic matter by microbes , in the presence of oxygen, to form a stable end product called compost. In the management of yard waste, this natural process decreases the need for landfill space and produces soil amendment as an end product.
Beneficial use and composting of yard waste may be practiced in the homeowner's backyard or in the waste management areas set up by townships and municipalities. Not all forms of yard waste lend themselves equally well to composting. In fact, woody materials such as tree trunks may be better managed and used by shredding into wood chips or saw dust, since wood is very resistant to composting. Leaves are most suitable for composting and provide the richest and most stable base of material and nutrients. With sufficient oxygen, water, and turnover, leaves can usually be broken down in a matter of weeks. Grass clippings decompose so quickly that they need to be mixed with slowerdegrading materials (such as leaves) in order to slow down and regulate the rate of decomposition . Control over the decomposition process is essential because of the potential for problems such as noxious odors. If the decomposition process is too rapid and proceeds without sufficient oxygen, the process becomes anaerobic and generates odors that can be highly unpleasant. In seasons other than fall, when the volume of leaves in yard waste is relatively small, many experts recommend that grass clippings be used as mulch rather than as compost to avoid the potential for odor.
In urban and mixed land use neighborhoods, yard waste may inadvertently contain plastics , papers, and other non-degradable materials. In some areas, the bagging of yard waste may involve the use of plastic bags. Depending on the efficiency of separation at the waste management area, these inert materials may find their way into the final compost product and lower the esthetics and usefulness of the compost.
[Usha Vedagiri ]