Page 93 - Materials Chemistry, Second Edition

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64 Waste Management Practices: Municipal, Hazardous, and Industrial
all other MSW. If a comprehensive materials recovery program is being considered, however, more
detailed data about waste categories will be needed — for example, wastes may have to be sepa-
rated into aluminum, ferrous metals, glass, and paper. In some cases, paper products are further sub-
divided into old newspaper (ONP), old corrugated cardboard (OCC), laser-quality office paper, and
colored paper.
One disadvantage of direct sampling programs based on a limited number of samples is that
data may be misleading if unexpected circumstances occurred during the sampling period. These
circumstances could include the delivery of infrequent and exotic wastes, a severe wet or dry sea-
son, or errors in sampling methods (U.S. EPA, 1999). Such errors will be compounded when a small
number of samples are collected to represent the community waste stream. Sampling studies do not
provide accurate information about trends unless they are performed in a consistent manner over a
long period of time (U.S. EPA, 1999). Another disadvantage of direct sampling is that it would be
prohibitively expensive for making estimates on a national scale.

4.2.2 MATERIAL FLOWS
Another approach to determining waste composition is to assess material flows. This method is use-
ful for estimating waste stream composition and trends on a regional basis. The U.S. EPA uses
materials flow estimation for the compilation of waste data for the United States (U.S. EPA, 2001).
The methodology is based on production data (by weight) for materials and products in the waste
stream. For a particular municipality, inputs and outputs are recorded and compared. For example,
if a community purchases 500,000 aluminum beverage cans in 1 week, it can be expected that about
500,000 aluminum cans will end up in the waste stream some time soon afterward. This model is,
of course, an oversimplification; and one must also consider that the community is an open system
having numerous imports and exports (U.S. EPA, 1999).

4.2.3 SURVEYS
Waste quantity and composition can be estimated by distributing questionnaires to producers of the
waste. This system typically applies to generators of commercial and industrial wastes, and does
not work effectively for domestic sources. A questionnaire is distributed to companies in an area,
with detailed questions concerning the quantities of waste generated and its composition. Waste
types may be listed in relation to product or material categories; for example, a county building may
be asked to quantify the laser-quality office paper, mixed, colored papers, ONP, and ONP boxes.
Other questions may pertain to seasonal variations in waste generation and any recycling programs
already in operation (Williams, 1998). In many cases, however, companies do not maintain accu-
rate records of the amount of waste generated. Data on composition may also be difficult to obtain
due to concerns over the release of company and proprietary information.
Yu and MacLaren (1995) compared the accuracy of direct waste analysis with the survey for
determining waste stream composition. Table 4.1 demonstrates that there is substantial variability
in material estimates between the two methods.

4.2.4 MULTIPLIERS FOR PROJECTING WASTE QUANTITIES

Waste generation multipliers are used for estimating waste quantities from sources in a particular
region. These multipliers express the relationship between the amount of waste produced and an
identifiable parameter, for example a household or a specific industry. The value of the multiplier is
based upon surveys, published data, and direct sampling for an area. For example, for a county in the
midwest United States, a household waste multiplier may be derived based on the size of the popu-
lation. Agricultural multipliers may be formulated based on the number and type of livestock and the
total land area available for grazing. Industrial waste multipliers may be based on the number of
employees at a facility. The population of the area in question is multiplied by the appropriate value