total cost are factors to be carefully weighed. Compost is
a good soil conditioner but a poor fertilizer. The process is
very attractive, but because of the factors mentioned has not
met with success in the United States.
The composting operation involves a combination of
steps. These may include: (a) weighing, (b) separation of
non-compostables and salvage by hand and by a magnetic
separator, (c) size reduction to 2 inches or less by means of a
shredder, grinder, chipper, rasp mill, hammermill, (d) ballis-
tic and magnetic separation, (e) biological digestion by any
one of a number of composting methods, (f) screening and
possible standardization of fertilizer value, and (g) disposal
by bagging for sale, or to a sanitary landfi ll.
Pyrolization Pyrolization as applied to solid wastes (metal
and glass removed) is an experimental thermochemical
process for conversion of complex organic solids, in the
absence of added oxygen, to water, combustible gases, tarry
liquids, and a stable residue. Intermediate products may
be collected or may be used to contribute heat to support
the process. The end products would be carbon, water and
carbon dioxide if carried to completion. If the raw material
contains sulfur and nitrogen, these oxides will be formed
with resultant air pollution unless provision is made for their
removal. Temperatures of 900–1700°F have been used. In a
variation, some oxygen and a temperature up to 2100°F is
used. It is a process of destructive distillation similar to that
used for making charcoal and for the recovery of organic
by-products such as turpentine, acetic acid, and methanol
from wood.^22 The Lantz converter and the Urban Research
and Development Corporation unit are variations of the
pyrolytic process. The Lantz system uses a temperature of
1200–1400°F with ground refuse.
High temperature incineration High temperature incinera-
tion is carried out at 3400°F (Melt-zit), 2500–2600 ° F (FLK
Slagging Incinerator, Germany), 2600–3000°F (Torrax
system), 3000°F (American Design and Development Corpo-
ration). These units are in the developmental and pilot stage.
Combustibles are destroyed and non-combustibles are reduced
to slag or sand-like grit. A 97% volume reduction is reported.
Wet oxidation Wet oxidation and anaerobic digestion of
refuse are in the experimental stage. In wet oxidation, the
refuse can be processed under high pressures and tem-
peratures, or the refuse can be ground and aerated while
in suspension in a liquid medium. In anaerobic digestion,
decomposable material is separated from refuse, ground and
then digested at controlled temperature in the absence of air.
The resultant gases are mostly methane and carbon dioxide
and the residue can serve as a soil conditioner.
Size reduction Shredders, hoggers, and chippers are devices
which reduce refuse, bulky items, and other solid wastes to
a manageable size for disposal by landfi ll or for processing
through an incinerator.
High density compaction High density compaction of solid
wastes is accomplished by compression to a density of more
than 66.5 pounds per cubic foot. The resulting bales may be
enclosed in chicken wire, hot asphalt, vinyl plastic, plain or
reinforced cement, or welded sheet steel depending on the
method of disposal or intended use of the bales or blocks.Rogus reports on the Tezuka-Kosan process in Tokyo that
liquid release during compression ranged from 2–5% by
weight and that it will require treatment. The bales had a
density of 70–109 pounds per cubic foot; they sank in sea
water; had good structural cohesiveness; resisted corrosion;
were reasonably free of odors, and insect, rodent hazard;
and showed no evidence of aerobic or anaerobic decomposi-
tion.^23 This system has not yet been adopted in the United
States but offers attractive possibilities for solid waste reuse,
economic hauling, and more acceptable disposal.
Other methods of achieving high density are subjecting
refuse to pressure in a hydraulic pressure chamber and forcing
baled refuse through a tube extending 30–50 feet below the
water surface. Plastic toys and containers do not remain com-
pressed or submerged. The effect of time on decomposition
with possible gas formation, disintegration and fl oating of the
refuse is not known. The long-term effect of the submerged
material on the marine ecology is also an unknown.^24IncinerationIncineration is a controlled combustion process for burning
solid, liquid, or gaseous combustible waste to gases and a
residue containing little or no combustible material when
properly carried out. It is a volume reduction process suit-
able for about 70% of the municipal solid wastes.
Incineration, if properly designed and controlled, is sat-
isfactory for burning combustible refuse provided air pollu-
tion standards can be met. Continuous operation six days a
week and a controlled temperature are needed for effi ciency,
prevention of excessive air pollution and odor control.
An operating design temperature range of 1500–1800°F
is generally recommended. Excessively high temperatures
and extreme variations cause cracking and spalling with
rapid deterioration of fi re tile and brick linings (refractories).
Batch feed or one-shift operation promote spalling and loos-
ening of tile linings. Other types of lining and design may
permit higher operating temperatures. Actually, the tempera-
ture in the furnace will range from 2100–2500°F. When the
gases leave the combustion chamber the temperature should
be between 1400 and 1800°F and the gas entering the stack
1000°F or less. The temperature will have to be lowered to
450–500°F before the gas is fi ltered or to 600°F or less if
electrical precipitators are used.Sanitary LandfillA sanitary landfi ll is an engineering method of disposing of
solid waste on land by spreading the waste in thin layers,
compacting it to the smallest practical volume and cover-
ing it with a layer of earth at the end of each day or more
frequently in a manner which prevents environmental pol-
lution.^25 The cost of sanitary landfi ll versus incineration for
various populations is shown in Figure 12.
Social and political factors An important aspect of refuse
disposal site selection, in addition to engineering factors, is
the evaluation of public reaction and education of the public so
that understanding and acceptance is developed. A program of354 ENVIRONMENTAL HEALTH
C005_009_r03.indd 354C005_009_r03.indd 354 11/18/2005 10:24:51 AM11/18/2005 10:24:51 AM