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.
Yard waste also is the largest single component of generated municipal solid waste (MSW) by weight, but it is a relatively small component of landfilled MSW by volume. Yard wastes' MSW market share in both generation and disposal declined dramatically in the last four decades. This has been because of dramatic increases in backyard compost piles, grasscycling and commercial composting operations.
Local yard waste generation varies dramatically based on climate, yard size and the percentage of the population in single family housing.
Yard Waste Municipal Solid Waste (MSW) Facts:
- 27.7 million tons or 12.6% by weight.*
- 205 pounds of yard waste per person.*
- In 1960, yard waste was 22.7% of MSW.
- 90% of yard waste is generated at homes and 10% at businesses.
- 12.5 million tons at composting facilities, for a 45.3% composting rate*
- 3,804 yard waste composting facilities in the United States in 1999.
- Ohio has more yard waste composting facilities than any other state.
Incinerated or Landfilled:
- 15.2 million tons or 9.4% of discarded MSW by weight.*
- In 1960, yard waste provided 24.2% of discarded MSW by weight.
- Yard waste has a per pound heating value of 2,876 Btus (a pound of MSW has 4,500 Btus to 5,000 Btus).
- Several states ban the burning of yard waste piles due to potential air pollution and health problems.
- Twenty-two states, with more than 50% of America's population, ban or restrict yard waste disposal.
- 21.7 million cubic yards or 5.1% of landfilled MSW in 1997.
- Uncompacted yard waste has a density of 250 pounds per cubic yard to 500 pounds per cubic yard.
- Landfilled yard waste has a density of 1,500 pounds per cubic yard.
- The U.S. Environmental Protection Agency (EPA), Washington, D.C., estimates that 11.7 million tons of yard waste were source reduced through grasscycling (leave-it-on-the-lawn) programs or backyard composting in 1996.
- Brush trimmings can be shredded and used as mulch by homeowners.
- Xeriscaping, which is landscaping with plants that need small amounts of water and produce small amounts of waste, also reduces yard waste.
- Large-scale leaf composting results in the loss of 40% to 75% of the original volume and 50% of the original weight of the leaves.
The Composting Process:
Composting is the 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 Fahrenheit to 140 degrees Fahrenheit), moisture content (40% to 60%) and an adequate carbon-to-nitrogen ratio are required. Insufficient aeration or a improper carbon-to-nitrogen ratio can cause intense odors. Improper operation can allow 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.
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 is used as a soil amendment and mulch by landscapers, farmers, nursery owners and the general public. Compost can be substituted for topsoil and mulches in parks, school grounds and highway verges. Farm soil restoration is a potential high-growth market. Compost also can be used as a daily cover for landfills.
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 per ton to $72 per ton.
Compost processors generally charge a tipping fee.
Chaz Miller is director of state programs for the Environmental Industry Associations, Washington, D.C. E-mail: [email protected] .
Biocycle, November 2000. Website: www.biocycle.com
Municipal Solid Waste Generation, Recycling and Disposal in the United States: Facts and Figures for 1998, U.S. Environmental Protection Agency Office of Solid Waste, 2000. Website: www.epa.gov/osw
Composting Council, Amherst, Ohio. Website: www.compostingcouncil.org
Measurement Standards and Reporting Guidelines, National Recycling Coalition, Alexandria, Va., Website: www.nrc-recycle.org
Municipal Compost Management, Cornell Waste Management Institute, Cobb and Rosenfeld, 1991. Website: www.cfe.cornell.edu/compost
National Source Reduction Characterization Report, U.S. Environmental Protection Agency Office of Solid Waste, Website: www.epa.gov/osw
Waste Age, September 1994. Website: www.wasteage.com
*1998 U.S. EPA estimates.