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2.5 Topic g: Waste characterization

In municipal waste management systems that rely almost exclusively on landfills, there is relatively little need to characterize the types and quantities of material disposed (unless, of course, this includes hazardous wastes). As communities in North America add source reduction, recycling, composting, and waste-to-energy (WTE) facilities to the system, the need for reliable data about what is in the waste stream has become paramount to the waste management program's success. Because each of these technologies addresses discrete segments of the waste stream, these data assist municipalities in: (a) determining the best management methods for different materials; (b) planning recycling and composting programs by identifying the amounts of recyclables and organic materials generated by residential, commercial, and possibly industrial sectors; (c) sizing WTE facilities based on the amount of wastes remaining in the waste stream after recycling and composting; and (d) estimating waste transportation and separation costs using local estimates of total municipal waste volume and weight.

Local waste characterization studies provide baseline data for municipalities to measure their progress toward specific waste management goals. In addition, projections of the size and composition of the future MSW stream helps communities plan MSW management facilities that often have operating lifetimes of several decades. The US Environmental Protection Agency estimates US national MSW generation using the "material flows" methodology, along with food and yard waste sampling data. The "material flows" model estimates MSW generation based on the production and consumption of materials that are found in the waste stream, with adjustments for imports, exports, and product lifetimes. These estimates do not include several commonly landfilled wastes, such as construction and demolition debris, wastewater treatment sludge, and non-hazardous industrial wastes. In addition, the data do not distinguish MSW generated from residential, commercial, and institutional sectors.

Using nationwide data for local planning is likely to lead to inaccurate estimates of local MSW quantities and composition, and could result in costly mistakes in purchasing equipment and sizing facilities. Local waste characterizations, on the other hand, are based on actual waste stream studies conducted at landfills, WTE facilities, materials recovery facilities (MRFs), or transfer stations. Good studies can provide information about the amount of specific products and materials generated by each sector (i.e., residential, commercial, or industrial), the amount of waste recycled, seasonal variations in the waste stream, and differences between urban, suburban, and rural areas. A study in San Francisco found that 33% of the disposed residential waste stream (i.e., post-recycling) was food waste, whereas yard waste only accounted for 7%. As a result, the city's backyard composting program focused on starting worm composting systems, since worms can degrade food waste more efficiently than other methods.

Comprehensive waste characterization studies are expensive in North America, costing from US$80,000 to upwards of US$150,000. While local governments can extrapolate data from other sources for initial planning purposes, it is generally felt that an actual sampling study should be performed before making significant capital investments. Waste characterization studies often include the following elements: (a) an approach to sample collection that ensures representative sampling; (b) four-season sorts of at least one week each; (c) multiple waste categories (e.g., about 25), with added detail on recyclables; (d) waste quantities by generation source; (e) an estimation of the heat value of waste if WTE is being considered; and (f) a survey of businesses, haulers, and brokers to quantify commercial recycling activities and disposal practices. A waste characterization can also include sample sorts of restaurant, hotel, office, and manufacturer waste to determine waste generation and characterization by sector, and curbside sorts to establish baseline data for tracking source reduction programs, household hazardous wastes, and program effectiveness.

Identifying generation rates and management methods for commercial waste is particularly important. On average, commercial waste accounts for 40% of the municipal waste stream in North America, but percentages vary by community. In Los Angeles, California commercial sources produced nearly two-thirds of the city's MSW in 1989. Conversely, some rural areas generate almost no commercial waste. Construction and demolition debris is sometimes a major portion of the waste stream and a good source of recyclable materials. Construction and demolition debris can be included in commercial waste estimates or broken out separately. In New Jersey, construction and demolition debris accounts for 25% of the waste generated, and 13.4% of the total waste recycled.

The composition of commercial and industrial waste in North America is significantly different from that of residential waste. Residential waste includes high volumes of paper, glass, food, and yard waste, whereas commercial and industrial waste includes a high volumes of paper, metals, and wood. The primary waste generators in the commercial sector tend to be hotels, restaurants, shopping centers, and hospitals. Waste characterization studies should be updated periodically to account for changes in population density, industrial concentration, and community affluence. In 1994, the province of Ontario passed legislation requiring all industrial, commercial, and institutional (ICI) operations employing more than 100 people to conduct waste audits and submit waste reduction plans. These plans serve two important purposes: they ensure the ICI sector is taking the necessary actions to achieve the national target of 50% waste reduction by 2000, and they provide local and provincial waste management staff with information on both the volume and composition of waste being generated.

To anticipate changes in the size and composition of the MSW stream and to make decisions concerning its management, local officials generally make projections of the future MSW stream based on the impact of at least two factors: (a) demographics; and (b) recycling, composting, and source reduction programs. Although consumer behavior and product composition also are important factors affecting MSW generation and composition, the impact of these factors is difficult to predict and can have an ambiguous overall affect. Some general trends are, however, evident. The percentage of paper and plastics in the waste stream is expected to continue increasing. Also, glass and steel containers are likely to continue to be replaced by lighter materials, such as aluminum and plastic. In addition, changes in local industry and commerce will affect the size and composition of the commercial and industrial waste streams.

Changes in the waste stream

Changes in MSW generation due to demographics can be broken down into two basic factors: (a) changes in population and (b) changes in per-capita generation. Population growth or decline due to changes in the birthrate, deathrate, or migration will significantly affect the generation of residential, commercial, and industrial MSW. At the national levels, North American populations are expected to continue to increase, but regions and localities can expect to see much more dynamic changes due to migration and other factors.

Over time, changes in MSW generation due to demographic factors have depended not only on population changes, but also on the amount and type of waste that each person generates (i.e., per- capita generation). Per-capita generation depends on at least three major factors: socioeconomic status, the degree of urbanization, and household size. The effect of socioeconomic status on MSW generation is uncertain. As North Americans have become more affluent on average, they have purchased more of all goods, which has increased waste generation. Although the majority of the population lives in urban areas, the degree of urbanization has some effect on MSW generation. Rural areas often have lower per-capita generation rates for at least some components of the waste stream (e.g., fewer newspapers because they are printed weekly rather than daily and are more often burned as fuel).

Recycling, composting, and source reduction initiatives have altered the MSW stream that is sent to WTE facilities and landfills. Since these programs reduce the portion of certain materials in the waste stream, the proportion of the remaining, untargeted components must necessarily increase.

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