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92 Waste Management Practices: Municipal, Hazardous, and Industrial
O

CH O C R
2

O

CHO C R'

O

O C R''
CH 2
FIGURE 4.13 Structure of a lipid molecule.

The biodegradability of the organic fraction of MSW can be determined via simple laboratory
tests for volatile solids and lignin content. The biodegradability factor can be calculated by the
equation (Tchobanoglous et al., 1993)

BF 0.83 – 0.028LC (4.8)

where BF represents the biodegradable fraction expressed on a volatile solids basis and LC the
lignin content of the volatile solids expressed as a percent of dry weight.
The biodegradability of several organic compounds in MSW is shown in Table 4.21. Wastes
with high lignin contents such as newspaper and cardboard tend to be of low biodegradability.
Materials with a low lignin content, for example food wastes and grass clippings, tend to have a
high biodegradability.

4.6 PHYSICAL PROPERTIES OF MSW

4.6.1 DENSITY
Density is a useful parameter in waste characterization as it provides information for predicting
storage volume, including as-discarded at a residence or commercial facility, after compaction in a
collection truck, and after compaction within a landfill cell.
The density of raw, uncompacted solid waste will vary as a function of composition, moisture
content, physical shape, and degree of compaction. With the increase in the proportion of glass,
ceramics, ashes and metals, the density also increases. Moisture will replace the air occurring in
voids, thus increasing density until it becomes saturated. Excessive water contents may actually dis-
place solids, which will eventually lower the overall density.
3
3
Raw wastes range in density from about 115 to 180 kg/m (200 to 300 lb/yd ). This low density
is partly a function of the shape of the material in the waste stream. Corrugated boxes, bottles, and
cans contain large void spaces which greatly decrease the density. If these materials were crushed,
waste density would sharply increase. Some compaction occurs during storage in piles. Shredding,
baling, and other size-reduction techniques also decrease irregularity and increase density (Liu and
3
Liptak, 2000). MSW compacted in a landfill ranges in density from 300 to 900 kg/m (Sincero and
Sincero, 1996; Kiely, 1997).
Volume reduction has a significant impact on the cost of collection and hauling MSW. Collection
trucks are space-limited; therefore, greater compaction capabilities will result in a greater density of
MSW and more cost-effective hauling. High-pressure compaction using stationary balers can greatly