Source separation

Source separation is the segregation of different types of solid waste at the location where they are generated (a household or business). The number and types of categories into which wastes are divided usually depends on the collection system used and the final destination of the wastes. The most common reason for separating wastes at the source is for recycling . Recyclables that are segregated from other trash are usually cleaner and easier to process. Yard wastes are often separated so they may be composted or used as mulch . Some experimental municipal recycling projects also require homeowners to separate household compostibles such as food scraps, coffee grounds, bones, and disposable diapers . Some studies suggest that as much as 30% of household waste may be compostible; another 40% may be recyclable.

Separate collection of household trash, recyclables, and yard waste is gaining popularity in the United States. In some communities source separation is mandated, while in others it is voluntary. Many cities provide residents with recycling bins to be filled with recyclables and placed next to garbage cans on collection day. Source-separated yard waste is usually placed in plastic bags or bundled if it is bulky, like tree trimmings. In areas where curbside collection of recyclables and yard waste is not available, residents often take these source-separated wastes to drop-off centers, or sell recyclables to buy-back facilities. For source-separated recycling programs to be successful, citizen participation is essential. Incentives to increase participation, such as reduced trash collection charges for recyclers, are sometimes implemented.

Household recyclables that are source separated from trash can either be commingled (all recyclables mixed together in one container) or segregated into individual containers for each material (i.e., glass, newspaper, aluminum ). Commingled recyclables are eventually separated manually, mechanically, or by some combination of both at transfer stations or materials recovery facilities. In some cases, commingled recyclables are manually separated at the curbside by the collection crew. Recyclables that residents have separated into individual containers are usually collected in trucks with compartments for each material. The collected materials are then processed further at materials-recovery facilities or other types of recycling plants.

Many businesses also separate their solid wastes. This can be as simple as placing recycling bins next to soda-vending machines in employee cafeterias or more complex separation systems on assembly lines. One of the most prevalent wastes from the commercial sector is corrugated cardboard (13% of municipal solid waste generated). Once it becomes contaminated by other wastes, it may not be suitable for recycling. Some businesses find it easier and more economical to separate and bale corrugated cardboard for recycling because this can reduce their waste-disposal costs.

Source-separation programs can reduce the undesirable effects of landfills or incinerators. For instance, batteries and household chemicals can increase the toxicity of landfill leachate, air emissions from incinerators, and incinerator ash. In addition, some potentially noncombustible wastes, such as glass, can reduce the efficiency of incinerators. Reducing the volume of residual ash is another incentive for diverting wastes from incineration .

Recyclables and special wastes can be retrieved from the waste stream without source separation programs. Many communities find it more convenient or economical to separate wastes after collection. In these programs, recyclables and special wastes are manually or mechanically separated at transfer stations or materials-recovery facilities. Separating recyclables in this way may require more labor and higher energy costs, but it's more convenient for residents since it requires no extra effort beyond regular trash disposal procedures.

Source separation may be only one part of an overall community recycling program. These, in turn, are components of more comprehensive waste-management strategies. To reduce the environmental impact of waste disposal, the Environmental Protection Agency (EPA) encourages communities to develop strategies to decrease landfill use and lower the risks and inefficiencies of incineration. Waste reduction and recycling are considered to be the most environmentally beneficial methods to manage waste.

[Teresa C. Donkin ]

RESOURCES

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U.S. Congress, Office of Technology Assessment. Facing America's Trash: What Next for Municipal Solid Waste. Washington, DC: U.S. Government Printing Office, October 1989.

U.S. Environmental Protection Agency, Solid Waste and Emergency Response. Characterization of Municipal Solid Waste in the United States: 1990 Update. Washington, DC: U.S. Government Printing Office, June 1990.

U.S. Environmental Protection Agency, Solid Waste and Emergency Response. Decision-Makers Guide to Solid Waste Management. Washington, DC: U.S. Government Printing Office, November 1989.