MANAGEMENT OF SOLID WASTE 661
hand where waste is utilized as fuel the possibility of using it
directly rather than converting it to fuel oil (Bureau of Mines
process) must be considered. Pyrolysis, hydro-oxydation
or similar processes should be competitive with direct fire
waste-heat recovery incineration where clean fuel is desired
or fuel is to be used at locations other than where the refuse
is available. The recovery of chemical raw materials from
refuse using these processes may also become attractive as
the process technology is refined.
The recovery of valuable products from incinerator efflu-
ent is not, however, being neglected. The Bureau of Mines has
demonstrated technology to recover metals and glass from
incinerator residues using high-intensity magnetic sorting as
well as chemical techniques at a cost of about $4 per ton.
ITT Research Institute has shown that refuse may be
selectively separated into a ceramic and metal slag when
incinerated at temperatures between 2800 and 3200°F. While
technically feasible, this separation incurs some severe eco-
nomic costs; it does yield some interesting products includ-
ing tiles, pipe and structural shapes. In addition to the newer
methods being studied, the use of incinerator fly ash and
even slag for road fill and concrete aggregate appears to be
attractive in some situations.
Specific process to convert refuse fractions are also
receiving attention and will be utilized in limited situations
where the economics are attractive. An engineering study hasshown that the organic portion of raw refuse can be economi-
cally converted to sugar by acid hydrolysis. This can then
be a raw material for alcohol production. One of the limita-
tions to this and similar processes is a limited market for the
product, and competition with other sugar sources as well as
other sources of alcohol; for example conversion of 3% of the
refuse to ethanol would saturate the normal market.
Though fuel use of alcohols is possible, only lim-
ited amounts of refuse can be converted using these pro-
cesses unless major shifts occur in our economy. Process
development to convert citrus waste to citric acid is being
conducted at the University of Florida. Other conversion
studies are being carried out, but all face the difficulties
inherent in processing a heterogeneous, complex, often
variable, mixture.
Of more than passing interest are studies being carried
out of the University of Maryland to obtain a protein concen-
trate for human and animal consumption from food processing
wastes. Similar studies at Louisiana State University, in the
pilot plant stage, has shown that agricultural cellulose wastes
can be broken down by selected microorganisms to yield a
low cost, high protein food. Yeast can also be produced from
cellulose wastes.
The use of waste as a “resource material” is still in its
infancy. It is gathering momentum quickly and in the next
decade should see significant changes in waste management.DELIVER PROCESS RETURN TOLBS. MATERIAL25 WATER10 METALS8 GLASS17FOOD
PLASTICS
YARD WASTES
TEXTILES40 PAPER(^100) 6.2 9.5 28.5 100
18 (PAPER)
37 (ENERGY)
2
4 (GLASS)
4
6 (IRON)
0.5 (ALUM.)
3.5
25
LAND
ATMOSPHERE
RECYCLE
FIGURE 5 Black Clawson Hydraposal-Fiberclaim. Material balance. Credit: Black Clawson Co.
C013_002_r03.indd 661C013_002_r03.indd 661 11/18/2005 2:27:22 PM11/18/2005 2:27:22 PM