658 MANAGEMENT OF SOLID WASTE
Studies by the Japanese indicate that the high pressure
squeezing and resultant elevated temperatures decrease
the BOD from 6000 in the raw refuse to 200 in the prod-
uct. Similarly the COD of 8000 (which compares to about
14,000 in US refuse) was reduced to about 150. Inspection
of the interior of the bale shows a homogenous, plastic like
mass. The bale will not support vermin, rodents, or insects
and is essentially odor free even if it is not protected by an
asphalt coating. The only other product of the compaction
is waste liquor, which amounts to 5% of the feed in Japan
and will probably be about 3% with US refuse because of its
lower moisture content.CompostingComposting is the biochemical degradation of organic
material (see: COMPOSTING) to yield a sanitary soil
supplement. Anaerobic composting has been practiced in
Asia and is the process by which sanitary landfills degrade
refuse. Modern composting has been practiced in Europe
for over 50 years using aerobic microorganisms. The prac-
tice has been attempted on a commercial scale in the United
States but with very limited success. The unattractiveness
of composting is primarily the result of American agricul-
ture’s orientation to chemical fertilizers. This has made the
large scale marketing of compost difficult. Composting,
while not economical now, could prove more attractive as
public opinion moves toward an attitude which requires
that wastes returned to the earth be compatible with the
environment.
Composting has one overriding advantage; it is the only
process which provides for recycling of organic residue. The
process can handle garbage and other organic refuse (but not
plastics) as well as sewage sludge and industrial waste from
certain operations such as saw and paper mills. The primary
disadvantages are cost, the need for fairly large areas for
final outdoor curing, a slight odor associated with a com-
posting plant, and lack of a market for the product.
Composting is practiced in several forms. Traditionally
rows of refuse, shredded or ground, four to six feet high,
are exposed to the environment and turned regularly. This is
known as the “windrow” method and is still used. Complete
composting can be achieved in 10 to 14 days, if seeding with
compost is employed, but often four to six weeks.
Mechanically aided aerobic composting is carried out
in a number of processes. Among the more prevalent are
the Dano process, the Earp-Thomas Multi-Bactor com-
post tower, and a number of cell-type stated tower systems.
Decomposition takes place under aerobic conditions with
the microorganisms supplied by seed compost. Typical
operating temperatures reach 130 to 140°F. Material is held
in the unit from one to six days depending on the process.
This is usually followed by an open air curing. A new plant
at Sehweinfurt, Germany, using the Caspari-Brikollare
process, produces briquettes in which from the compost is
stored until it is to be used.
Raw materials suitable for aerobic composting will be
finely ground (coarse for windrowing) and have a maximumcarbon to nitrogen ratio of 50 to 1. It is important that good
dispersion of air can be achieved and that the moisture level
be maintained between 50 and 60%. Recycling of between
1 and 10% of active compost enhances the composting pro-
cess by minimizing the time required for sufficient microor-
ganisms to develop. The yield from composting is about one
volume for every three volumes of feed; the weight yield is
between 30 and 40%.
In Europe compost is utilized as an organic soil condi-
tioner in luxury agriculture such as vineyards, hotbed vege-
table farming, flower and seed production, fruit farming and
the improvement of recreational land. It has found little or no
use in basic agriculture, nor is it used for erosion control. In
Germany less than 1% of the domestic refuse is composted
and in Holland only about 15% is so treated. There appears
to be no increase in composting operations because of a lack
of additional marketing opportunities.
The investment for a composting facility varies widely
depending on size and process. Investments of between
$7500 and $12,000 per daily ton of capacity have been
reported; no valid average figures can be reported because
there are so few operational plants. Operating costs,
including the cost of capital, will vary between $8 and $12
per ton of refuse (assuming labor at $15,000 per man year)
on a US basis. European investments appear to be as low
as $1000 per daily ton and operating costs in 1964 were
between $3.20 and $6.60 per ton, with an average of $4.50
per ton of refuse.^30 Part of this cost was recovered by sale
of salvage (16¢ per ton) and compost; the average recov-
ery amounted to $1.17 per ton resulting in a net average
cost of $3.38.^31The Economics of Waste DisposalEconomic considerations have and will, of course, continue
to play a significant role in the choice of waste management
method. Table 21 summarizes both operating and invest-
ment costs for principal waste processing methods. It must
be realized that values can vary widely depending on local
conditions. Technological improvements can also alter the
price structure. Most important, however, is the fact that long
range implications of waste management, environment and
resource considerations cannot readily be reduced to a quan-
titative cost, and these factors should weigh heavily in the
choice of a waste processing method.Reclamation, Reuse and ConversionThere has been a salvage industry as long as there has been
waste. The intensity of this effort has been limited how-
ever and varies very much with location as well as the eco-
nomic situation at the time. No concentrated effort, except
perhaps in wartime, has ever been made to recover and
recycle a high percentage of waste. True landfill can be
considered a form of reclamation but it is a very low grade
use of refuse. This is not to say that the salvage industry is
small: the latest figures indicate that it has sales in excess
of $10 billion per year.C013_002_r03.indd 658C013_002_r03.indd 658 11/18/2005 2:27:21 PM11/18/2005 2:27:21 PM