Profiles in Garbage: Food Waste

Food waste includes uneaten portions of meals and trimmings from food preparation activities in kitchens, restaurants and cafeterias.

Food waste is the third largest component of generated waste by weight, after yard waste and corrugated boxes. However, due to a low composting rate, food waste is the largest discarded waste component by weight.

From the early 1960s until 1996, the amount of food waste slowly increased, according to U.S. Environmental Protection Agency (EPA), Washington, D.C., data.

In 1996, a U.S. Department of Agriculture (USDA), Washington, D.C., Economic Research Service study and two curbside sampling studies showed that food waste was generated at a much higher rate than EPA's database originally said was possible.

As a result, EPA changed its food waste generation methodology and increased its food waste estimates for each year in the 1990s. EPA did not revise estimates for previous years.

Even with the revised data, food waste's share of the solid waste stream has decreased in the past 35 years, largely due to increased consumption of packaged, processed foods.

Generated: - 22.1 million tons or 10% by weight. superscript *

- 163.7 pounds of food waste per person. superscript *

Composted: - 600,000 tons for a 2.6% recovery rate superscript *

- Food waste is organic and highly compostable. Grocery store food processing trimmings are a prime resource for composting facilities.

- Only three states, Minnesota, New Jersey and Washington, reported recovering more than 10% of generated food waste in 1997.

- 95 off-site food waste composting facilities operated in the United States in 1999. Most of these facilities are small in size with yearly throughputs that can range from 5 tons to 100 tons.

Incinerated or Landfilled: - 21.5 million tons or 13.6% of discarded MSW by weight. superscript *

- Food waste usually is the wettest component of the waste stream with a typical moisture content of 70% and a Btu value ranging from 1,500 Btus to 3,000 Btus per pound compared to 4,500 Btus to 5,000 Btus in a pound of MSW.

Landfill Volume: - 21.4 million cubic yards or 5.3% of landfilled MSW in 1996.

- Food waste can decompose into methane in a landfill. EPA landfill regulations are designed to limit potential environmental degradation from methane production.

Density: - Landfilled food waste has a density of 2,000 pounds per cubic yard.

- Food scraps, and solid and liquid fats have a density of 412 pounds in a 55-gallon drum.

Source Reduction: - Food processing companies that prepare canned or frozen agricultural products for home consumption eliminate food waste from MSW.

- In-sink kitchen disposal units transfer disposal of food waste from the solid waste system to the wastewater system.

The Composting Process: Composting is the controlled decomposition of organic matter by microorganisms into a humus-like product. Techniques such as windrows, the most popular technique for composting food waste, static piles and in-vessel systems generate energy and heat and destroy pathogens. Water and carbon dioxide dissipate into the atmosphere during this process.

Temperature control (132 to 140 degrees Fahrenheit), moisture content (40% to 60%) and an adequate carbon-to-nitrogen ratio are required. Insufficient aeration or improper carbon-to-nitrogen ratio can cause intense odors. Food wastes tend to have higher nitrogen content than other compostables. Improper operation allows aspergillus fumigatus, to grow on compost piles, causing health problems.

It takes three to 12 months to produce compost, depending on the process and type of food wastes being composted.

Composting Markets: Food 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 find a market as a soil amendment and as mulch for farming, horticulture, landscaping and home gardens. Compost also can be used in erosion control and roadside landscaping. Lower quality compost can be used as landfill cover or in land reclamation projects.

Landscapers and homeowners were the biggest compost markets in an U.S. Composting Council (USCC) survey (the survey covered compost made from a variety of organics).

Soil amendments, mulch, growing media component, topdressing, garden bed establishment and erosion control were the top uses identified for compost in the same survey.

End-Market Specifications: Each end-market has its own specifications. Generally, non-organic materials (glass, metals, plastic bags, etc.) must be kept separate from food waste.

Composting Cost and Value: Food waste composting facilities usually charge a tipping fee for incoming materials. Generally, tipping fees in 1999 were in the $25 per ton to $35 per ton range.

Prices for finished compost vary widely. A USCC survey showed an average wholesale price of $9.87/per cubic yard and an average retail price of $18.07/per cubic yard (these prices reflect compost made from a variety of organics).