Environmental Engineering Reference
In-Depth Information
8
Incineration
153
destroying weed seeds, insect larvae, and potential plant and human pathogens.
The temperature is measured with a long-stemmed thermometer at a depth of at
least 18 inches into the volume of material collected. Temperatures above 140
◦
F
will begin to limit microbial activity, and temperatures in excess of 160
◦
F can
kill soil microorganisms. The pH of materials should be monitored, and a value
6.5 to 8 should be maintained. The role of bacteria in composting increases in
importance with the increase in pH.
Factors to be considered in starting composting programs include available
space and equipment, management personnel, capital and operation cost, and
opportunity cost. A composting program could prove a viable alternative for
management of yard waste and could help to reduce landfilled solid waste and
disposal costs. Materials such as grass clippings and leaves collected through
semiannual installation cleanups, waste from riding stables, and shredded clas-
sified documents could be useful for initiating a composting program. Dense
materials such as trees and limbs are not suitable for composting due to their
slow rate of decomposition, which will make the program expensive in operation
as a result of long-term use.
Food waste is ideal for composting because of its high moisture content and
susceptibility to odor production and large quantities of leachate. Fruits, veg-
etables, dairy products, grains, bread, unbleached paper napkins, coffee filters,
eggshells, meats, and newspaper can be composted. Items unacceptable for com-
posting include condiment packages, plastic wrap, plastic bags, foil, silverware,
and drinking straws. Red meat, bones, and paper are acceptable, but they take
longer time to decompose and thus are not preferred. Odor can be prevented by
keeping the compost pile well aerated and free of standing water. Leachate can
be reduced through aeration and by adding sufficient amounts of high-carbon
bulking agent. Preconsumer food waste is easy to compose because it is gen-
erally separated from the rest of the waste stream generated, thus reducing the
possible presence of contaminants in future compost. Postconsumer food waste
is challenging because of separation issues involved, as the food waste is already
mixed with general waste stream, thus increasing the presence of contaminants.
This problem can be reduced by having a separate trashcan for only food waste.
8
INCINERATION
The major purpose of using incineration is to reduce the volume of the MSW so
that the landfill space can be saved. Depending on the feed MSW composition, the
volume can be reduced by 70 to 90 percent. Incineration is a thermal process used
to convert the organic portion of the MSW to gases and the inorganic portion
to ashes. There are two major types of incineration plants. One is mass-burn,
which burns the commingled MSW, and the other is RDF-fired, which burns the
refuse-derive fuel. There are three major issues with the incineration facilities:
(1) the incineration plant is more expensive compared to other disposal facilities
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