Page 262 - Materials Chemistry, Second Edition

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Composting MSW 233
● Covering compost beds and cured piles
● Percolating contaminated water through soil so as to absorb and break down organic
compounds
● Building retention ponds to prevent discharge of runoff to surface water

8.8.7 VECTORS
Vectors are small animals or insects that carry disease. Mice, rats, flies, and mosquitoes may occur
at composting facilities. Rodents can be attracted by the food and shelter available at composting
facilities (particularly MSW composting operations) and can be difficult to eliminate. Flies, which
can transmit salmonella and other food-borne diseases, are often carried in with the incoming mate-
rial and are attracted to piles that have become anaerobic. All life stages of the housefly are killed
by the temperatures attained in the compost pile (Golueke, 1977). Mosquitoes, which can also trans-
mit disease, breed in standing water. Keeping the processing area neat can control insects; also,
maintaining aerobic conditions and proper temperatures in the piles and grading the area properly
to prevent ponding will limit mosquito breeding.

8.8.8 FIRES
If the compost material dries out and becomes too hot, spontaneous combustion may occur in the
pile (Figure 8.11). Organic material can ignite spontaneously at a moisture content of between 25
and 45%. This is unlikely, however, unless the material reaches temperatures higher than 93°C
(199°F). The site must be designed for access by firefighting equipment including clear aisles
between piles or windrows, and must have an adequate water supply (Richard et al., 1990).
Key conditions that lead to spontaneous combustion are biological activity, relatively dry mate-
rials or dry pockets, large well-insulated piles, limited airflow, and sufficient time for the tempera-
ture to build up. Other contributing factors may include short circuiting of airflow, a nonuniform
mix of materials, poor moisture distribution, and inadequate monitoring of temperature and other
variables. These conditions tend to be more common within large undisturbed piles containing raw
feedstocks, curing compost, and finished compost than in the active composting system. Actively

FIGURE 8.11 Compost fire presumably initiated by spontaneous combustion. Reproduced with kind permis-
sion of Winchester News-Gazette, Winchester, IN.