Page 41 - Materials Chemistry, Second Edition

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12 Waste Management Practices: Municipal, Hazardous, and Industrial
Surface Mining Control and Reclamation Act (SMCRA) of 1977—mine operators are required to
return the affected site to its previous contours and land use, and must post a sufficient bond until
all operations are satisfactorily completed.
Quantitative estimates of mine wastes produced in the United States are limited; estimates range
from 1 to 2 billion tons annually. Approximately one half occurs as overburden spoils, and the
remaining one half as heap leach waste (Rhyner et al., 1995).

1.2.9 AGRICULTURAL WASTE
The largest proportion of agricultural wastes occurs as animal manures and crop residues; however,
other wastes, such as pesticide containers and packaging also contribute to this category.
In the United States, agricultural wastes are produced in much greater quantities than are
municipal solid wastes. Much of this waste goes unnoticed by most Americans, however, as the
sources are more diffuse and wastes are generated in areas of low population density. In small-
scale agricultural operations, animal and plant wastes can be recycled directly on to the soil sur-
face. Used on-site, this process can be viewed as the application of an inexpensive soil amendment
(Figure 1.5). However, when large numbers of animals are concentrated in a relatively small area,
for example in livestock feedlots and poultry operations, the accumulation and management of the
wastes become a more acute concern. Manures may need to be moved off-site for disposal; cost
and feasibility issues become significant, as manures are composed mostly of water and are there-
fore only a dilute source of plant nutrients. Problems related to odor, pathogen content, salt con-
centration, and ammonia production are also present. In such cases, more sophisticated
management techniques may be required to reduce the volume and potential toxicity of the wastes
(e.g., anaerobic digestion or composting), thereby rendering the material more cost-effective for
transport as well as hygienically safe.

FIGURE 1.5 Animal manures applied to agricultural fields serve as a low-cost soil conditioner and source
of nutrients.