MANAGEMENT OF SOLID WASTE 657
wastes such as water containing organics are incinerated. The
special applications are numerous, including the incineration
of radioactively contaminated wastes.
In addition to the more traditional incinerators, whether
rectangular or cylindrical, special designs are employed in
industrial waste disposal. For example shredded plastic^24
as well as “white water” from paper-mills^25 is incinerated
in a fluidized-bed combustion chamber. Industrial sludge
is being burned in a rotary kiln^26 by Kodak. Dow Chemical
has had a rotary kiln on line for over 20 years handling a
mix of refuse and industrial waste. Solid cyanide waste in
automobile plants is put into solution and then burned while
aluminum chloride sludge from a petrochemical operation
can be burned to produce HCl and alumina.
Although hauling to landfill sites is the present disposal
method for many industries, on-site incineration of indus-
trial wastes will receive wider use for waste disposal where
recycle is not possible and volume is sufficient, in excess of
500 lb/day, to justify an installation.
Hospital wastes are now commonly being disposed of
in onsite incinerators. To eliminate the possibility of spread-
ing infection, wastes should be promptly incinerated. This is
best done in an onsite facility. The average load for hospital
incinerators is about 20 pounds per day per patient with a very
high fraction of garbage and paper and plastic throw-away
products.^27 Provision must also be made to handle pathologi-
cal wastes, therefore combustion temperatures should be in
excess of 2000°F and adequate residence time for the gases
at 1500°F should be provided.Refuse-Derived FuelIn the past there has been some objection to direct firing of
refuse. Partly these are aesthetic in nature and partly theyresult from the high variability of raw refuse. At one time, it
was thought that firing of coal and refuse might overcome a
number of these problems. Indeed it did, but not the institu-
tional problems of handling raw refuse. As a result several
processes were developed to produce refuse-derived fuel
(RDF). These processes have been in development for the
past ten years and have not found, to date, wide commer-
cial application. Essentially, raw refuse is separated into the
organic and paper portion, and the recoverable, recyclable
components, such as ferrous metal, aluminum, glass. This sepa-
ration is carried out after shredding, as discussed under the
section on Reclamation, Reuse and Conversion. The shred-
ded material can then be fed as is; and that form is the lowest
grade of RDF. Some cases it is palletized, and fired as pel-
lets. Palletizing reduces handling problems and increases
storability at the expense of an additional processing step.
RDF has been successfully co-fired with coal and it is antici-
pated that over the next ten years a number of RDF fired
power boilers will be installed either for steam generation or
electric power generation.CompactionThe reduction of waste volume is receiving considerable
attention in an effort to reduce collection costs; compaction
is one of the favored methods to achieve this reduction. High
pressure compaction has been developed by Tezuka Kosan
of Japan to provide a high density product suitable as an
essentially inert fill or even as a building material.^28 Using
this product as a base covered with a minimal earth over,
the Japanese have reclaimed land from tidal areas having a
water depth of 10 feet.^29
The Japanese process shown in Figure 4 collects refuse
and subjects it to three stages of compression with the final
main press exerting 3000 psi on the refuse. The resulting
bale is usually wrapped in chicken wire and coated with
asphalt for ease of handling and to prevent crumbling and/
or leakage. The bales have a density of between 1900 and
2300 pounds per cubic yard and result in a volume reduc-
tion of about 90%. This compares to densities of about 1200
to 1500 pounds per cubic yard achieved in lower pressure
compaction. The product bale is inert and such bales have
survived exposure in Tokyo Bay for three years to date with-
out visible signs of degradation.TABLE 20
Incinerator ash and slag analysis^24SiO 2 46% Na 2 O3%
Al2O 3 21% K 2 O1%
Fe2O 3 8% P 2 O 5 2%
TiO 2 3% BaO 0.6%
CaO 10% SO 3 0.3%
MgO 3% ZnO 0.5%TABLE 19
Incinerator residue composition ranges^23Wt.%Moisture 24–40
Components, Dry Wt. Basis
Tin cans 16–22
Iron, all types 9–14
Nonferrous metals 0.1a–3.7
Stones and bricks 0.8–1.9
Ceramics 0.6–1.5
Unburned paper and charcoal 4–12b
Partially burned organics 0.1–1.3b
Ash 12–18
Glass 37–50a After hand picking.
b High temperature operation will decrease this
markedly.C013_002_r03.indd 657C013_002_r03.indd 657 11/18/2005 2:27:20 PM11/18/2005 2:27:20 PM