Page 217 - Materials Chemistry, Second Edition

CAT3525_C07.qxd 1/29/2005 9:57 AM Page 188
188 Waste Management Practices: Municipal, Hazardous, and Industrial

FIGURE 7.17 Pelletizer (densifier) for shredded organic wastes in the manufacture of RDF.

removed the box for shipment to a sanitary landfill. This system was ideal for dry wastes. Some busi-
nesses and industries, however, such as restaurants and hospitals, disposed of liquid as well as solid
wastes. Because the compactor was separate from the container, liquid wastes resulted in spills and
residue. This residue left an odor and attracted animals and insects. In response to this practical prob-
lem the self-contained compactor was developed. Self-contained compactors were simply a com-
pactor and a roll-off box housed together in the same unit. For hauling, the electrical power unit was
separated from the assembly. Self-contained units typically included a liquid collection area situated
directly beneath the compactor to contain any spillage (Ely, 1993).

7.4.3.3 Baler
A baler (Figure 7.18) is one of the more common components of the MRF waste processing system.
Balers are used for producing bales of corrugated cardboard, newspaper, high-grade paper, mixed
paper, aluminum cans, and plastic containers (Figure 7.19). Balers are available with a wide range of
horsepower and levels of sophistication. Some balers have fully automated operation while others
require a significant amount of work by an operator. As previously discussed, many industrial buy-
ers have specific requirements for any secondary materials purchased; therefore, the market specifi-
cations for a particular product should be determined before a baler is selected (U.S. EPA, 1991).
Most balers are of sufficiently low force that, once released, the baled product will simply
rebound to its original form. Hence, bales must be tied, either with steel wire, high-tension nylon
string, or similar durable material. However, some high-power balers apply sufficient force such
that a bale will maintain its shape even after the force is removed. Of course, such balers tend to be
much more expensive and maintenance-intensive than the low-force models. The original waste
input material will also influence the necessity of tying a bale. Bales of aluminum or other metal
will hold their form better than would bales of HDPE containers or old newspaper, for example.
The performance of baling and compaction equipment is measured by calculating the percent-
age volume reduction and the compaction ratio. Percentage volume reduction is calculated by the
equation

Volume reduction (%) (V − V )/V 100 (7.8)
i
f
i
3
where V is the initial volume of wastes before compaction (m ), and V the final volume of com-
f
i
3
pacted wastes (m )