Yard waste includes grass, leaves, and tree and brush trimmings. Grass is the largest yard waste component by weight, while leaves are the largest component by volume. Grass is the largest component of yard waste in the summer, while leaves are largest in the fall. In these two seasons, yard waste often is the largest solid waste component.
Yard waste also is the largest single component of generated municipal solid waste (MSW) by weight and one of the largest components of landfilled MSW by volume.
However, yard waste's MSW market share has been steadily declining.
Yard Waste Municipal Solid Waste (MSW) Facts: Generated: * 27.7 million tons or 12.8% by weight.*
* 205 pounds of yard waste per person.*
Composted: * 11.5 million tons at composting facilities, for a 41.4% composting rate*
* 3,807 yard waste composting facilities in the United States in 1998.
* Alaska is the only state with no yard waste composting facilities.
Incinerated or Landfilled: * 16.2 million tons or 10.4% of discarded MSW by weight.*
* Dry yard waste has a per pound heating value of 2,876 Btus (a pound of MSW has 4,500-5,000 Btus).
* Several states ban the burning of yard waste piles due to potential air pollution and health problems.
* 24 states ban or restrict yard waste disposal.
Landfill Volume: * 21.7 million cubic yards or 5.1% of landfilled MSW.*
* Uncompacted yard waste has a density of 250 to 500 pounds per cubic yard.
* Landfilled yard waste has a density of 1,500 pounds per cubic yard.
Source Reduction: * Backyard composting and "leave-it-on-the-lawn" (grasscycling) programs are the primary forms of source reduction for leaf and grass waste.
* The U.S. Environmental Protection Agency (EPA), Washington, D.C., estimates that 11.7 million tons of yard waste were source reduced through grasscycling or backyard composting in 1996.
* Brush trimmings can be shredded and used as mulch by homeowners.
* Large scale leaf composting is a volume reduction resulting in a 40 percent to 75 percent loss of the original volume and 50 percent of the original weight.
* Xeriscaping, which is landscaping with plants that consume minimal amounts of water and produce minimal amounts of waste, is another yard waste source reduction measure.
The Composting Process: Composting is controlled decomposition of organic matter by microorganisms into a humus-like product. Techniques such as windrows, static piles and in-vessel systems generate energy and heat, and destroy weeds, plants and human pathogens. Water and carbon dioxide dissipate into the atmosphere during this process.
To maintain aerobic conditions, yard waste usually is turned to provide oxygen for the composting organisms. Temperature control (132 degrees to 140 degrees Fahrenheit), moisture content (40 percent to 60 percent) and an adequate carbon-to-nitrogen ratio are required. Insufficient aeration or an improper carbon-to-nitrogen ratio can cause intense odors. Improper operation allows a fungus, aspergillus fumigatus, to grow on compost piles, causing health problems.
Compost can be produced in three to 18 months, depending on the process and amount of yard waste used.
Composting Markets: Yard waste compost is not a fertilizer. It is a useful soil conditioner that improves texture, air circulation and drainage. Compost can moderate soil temperature, enhance nutrient and water-holding capacity, decrease erosion, inhibit weed growth and suppress some plant pathogens.
High quality compost can be marketed as a soil amendment and as mulch for landscapers, farmers, nursery owners and the general public. Compost can be used for highway verges, parks and school grounds in place of topsoil and mulches. Farm soil restoration is a potential high-growth market. Compost also can be used as a daily cover for landfills.
End-Market Specifications: Each end-market has its own specifications, with limits on moisture and other potential contaminants. Generally, non-organic materials (glass metals, plastic bags, etc.) must be kept separate from yard waste. Tests show little heavy metal contamination of yard waste.
Composting Cost and Value: A U.S. Composting Council, Amherst, Ohio, study of yard waste composting facilities showed an average processing cost of $25 per ton, with a median of $16 per ton and range of $8 to $72 per ton.
Compost processors generally charge a tipping fee.
Biocycle, April 1999.
"Characterization of Municipal Solid Waste in the United States: 1998 Update," 1999 U.S. Environmental Protection Agency Office of Solid Waste, Washington, D.C. Website: www.epa.gov/osw
National Source Reduction Characterization Report, 1999
Composting Council, Amherst, Ohio. Website: www.compostingcouncil.org
Municipal Compost Management, Cornell Waste Management Institute, Cobb and Rosenfeld, 1991. Website: www.cfe.cornell.edu/compost
National Recycling Coalition, Alexandria, Va., Measurement Standards and Reporting Guidelines. Website: www.nrc-recycle.org
Waste Age, September 1994. Website: www.wasteage.com
* 1997 U.S. EPA estimates