Composition Studies: Get To Know Your Waste

John S Savage and Stacey T. Demers

Some say you really don't know your solid waste until you sort it by hand. In fact, you may be surprised by what you find.

Over the last 10 years, many communities have taken a scientific approach to learn more about their waste. By contracting the manual sorting of residential refuse samples, they hope to use the information to establish the appropriate collection, recycling, composting and waste-to-energy programs.

For some communities, these waste composition studies may tell them what they already suspected. For others, a study may demonstrate seasonal variations in set-outs for certain materials. Planning ahead for such changes could help communities save program costs and boost capture rates.

The Study Basics On the East Coast, eight municipalities recently conducted waste characterization studies to determine variations in corrugated cardboard, newspaper, aluminum beverage cans, ferrous food containers, yard waste, high density polyethylene (HDPE) and polyethylene terephthalate (PET) plastic containers, clear and colored glass containers and household hazardous wastes (HHW).

The communities included Volusia County, Fla.; Fairfax County, Va.; Durham County, N.C.; Orange County, N.C.; Montgomery County, Md.; New York City, N.Y.; Onondaga County, N.Y.; and Broome County, N.Y.

The municipalities contracted SCS Engineers, in Reston, Va., to sample random refuse loads from residential vehicles at processing facilities, landfills, waste-to-energy facilities and transfer stations. To account for daily variation in waste composition, samples were taken over a one-week period. On average, 30 samples were taken from the residential waste generators each season.

Summer sampling was performed in July, August and September; winter in January, February and March; fall in October, November and December; and spring during April, May and June.

For the New York City study, waste was analyzed according to medium income generators in low, medium and high population densities.

Form A Hypothesis Before launching the waste composition studies, the communities outlined what they expected to find. For example, given the areas' climate, the communities expected that yard waste volumes would increase in spring, summer and fall.

Further, it was anticipated that quantities of aluminum beverage cans and PET soft drink containers would be higher in the warmer months since that's when more fluids are likely consumed.

Finally, the communities expected that the household hazardous wastes fraction would be greater during the warmer months, when residents often undertake spring cleaning, gardening and landscaping projects and home repair/renovation.

Right Or Wrong? After sorting and counting numerous volumes of waste, the communities discovered that some seasonal variation occurred in all of the waste characterization studies. Generally, greater seasonal variation occurred in geographic locations with large temperature ranges between winter and summer.

However, most of the communities' hypotheses did not hold true. For example, no pattern was found for aluminum or PET beverage containers. Nor were patterns observed for OCC, HDPE or glass.

Although most of the communities experienced significantly higher or lower HHW quantities during a particular season, no single disposal pattern was observed.

As expected, quantities of yard waste are significantly lower in winter. Yard waste bans and separate collection programs also have contributed to significant decreases in recent years.

An unexpected result was seasonal variations in ferrous food containers in Fairfax County, Va., New York City and Montgomery County, Md., all of which had higher quantities of this material in winter (see chart on page 58). One reason may be that consumers substitute canned foods for fresh foods during the winter months when fresh foods are less common and more expensive.

It's important to understand that waste composition categories are dependent variables; that is, an increase in one material results in a decreasing percentage of the waste stream available for the remaining categories. As a result, it can be difficult to establish seasonal variation.

Planning Around Results With the exception of a few materials, each community examined has its own unique disposal rhythm. It's worthwhile for solid waste managers and recycling coordinators to get to know their own particular waste streams. For a more complete picture of seasonal disposal patterns, managers should collect both composition and generation data.

The amount of each material disposed and available for diversion to a recycling program will vary by season for each community. Since a greater percentage of ferrous food containers are disposed during the winter, these municipalities could consider boosting capture of this material during those months.

In addition, solid waste managers should be aware that the flow of materials to the composting/processing facility will be significantly reduced during the winter months. In most cases, the fall leaf collection will yield the greatest volume of yard wastes. Consequently, the facility must provide adequate storage for these materials.

When conducting waste composition studies, remember that the face of the waste stream changes constantly. Source reduction and recycling initiatives, disposal bans and separate collection and disposal programs (e.g. HHW), all can change your waste composition "pie."

Communities perform waste characterization studies for many reasons. First, they can provide accurate baseline data to help track the progress of a waste reduction program. Second, they can quantify the amounts of recyclable materials available for marketing. Last, they can help monitor your program's effectiveness by assessing which recyclables are "passing through" collection programs and being disposed.

To select the best study method, first determine the information desired and its use. Next, evaluate the waste streams to be surveyed, the desired precision level and the resources available. Finally, decide whether a full-scale waste characterization study or a recyclables potential assessment is best for you.

Full-Scale Characterization. For statistical validity, a typical waste characterization study involves:

* Week-long sampling to account for daily variations and quarterly sampling to establish seasonal changes;

* Randomly selecting 30 grab samples from residential and commercial/industrial waste loads;

* Setting sample weights at 200 to 300 pounds; and

* Sorting wastes into 30 to 40 component categories.

Typically, a week-long, full-scale waste characterization study costs $18,000 to $25,000, including data analysis and report writing. Thus, a four-season study would cost $72,000 to $100,000.

Recyclables Potential Assessment. A recyclables potential assessment (RPA) is a two- to three-day waste composition study that can provide quick, reasonably quality data. RPAs can target certain recyclable materials as well as other waste stream components such as household hazwastes (HHW), C&D debris and yard wastes. RPAs can help communities:

* To assess the success of current residential (including single-family or multi-family housing), commercial or institutional recycling programs;

* To identify public education and information needs for each generator to encourage waste reduction;

* To identify additional materials to be included in a recycling program; and

* To assess the effectiveness of landfill bans and HHW collection programs;

Because RPAs cover shorter periods of time, their results do not account for variations in daily or seasonal composition. RPAs also study a reduced number of samples.

In general, a RPA costs between $8,000 and $12,000, depending on the size of the waste stream. Costs are lower for RPAs due to fewer categories (approximately 15) and a shorter sampling period compared to a full-scale study.

Once managers decide what information they're seeking, they can tailor a study to fit their needs.