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136 Waste Management Practices: Municipal, Hazardous, and Industrial
adversely affect animals using the bedding or the soil where the bedding is applied as a component
of manure (Rhyner et al., 1995).
Refuse-derived fuel (RDF) is a mostly carbonaceous material derived from MSW. The non-
combustible components of waste such as stones, glass, and metals are removed usually by mechan-
ical means, the organics are shredded, and the resultant “fluff” is either used directly as a fuel or is
compressed into pellets. RDF is typically burned as a co-fuel along with coal, which accrues a num-
ber of environmental and economic benefits. A detailed discussion of RDF appears in Chapter 9.

6.7.4 BENEFITS OF PAPER RECYCLING

Seventeen trees are required to produce 1 ton of paper. All Sunday newspapers in the United States
require the equivalent of one-half million trees every week. When paper is manufactured from waste
paper, however, trees are conserved as are considerable amounts of energy. For 1 ton of paper recy-
cled there is a savings of approximately 4100 kWh of energy along with 7000 gal of water and 3 yd 3
of landfill space (Liu and Liptak, 2000). Paper production from recycling also requires less chemi-
cals, including bleaches, and will therefore produce less toxic wastes.

6.8 GLASS

6.8.1 GLASS MANUFACTURE
The ancient Egyptians were the first society known to manufacture glass for containers, by first
forming a sand or clay mold and then wrapping strands of molten glass around the mold. A more
widespread use of glass as a packaging material was made possible by the development of glass
blowing in about 50 B.C.E. Across the Atlantic Ocean, glass manufacturing was the first known
industry in Pre-Colonial America, developed more than 10 years before the arrival of the Pilgrims
in 1620. Techniques for mass production of glass containers were developed in the 19th century and
the first fully automatic bottle machine, producing one million bottles per week, was developed in
1903. Today, approximately 10 million tons of glass containers are manufactured in the United
States annually (ISRI, 2001).
In order to manufacture new glass products, relatively inexpensive raw materials are required,
including silica (SiO ), soda ash (Na CO ), and limestone (CaCO ). Sometimes muriate of potash
2
2
3
3
(KCl) is used in place of soda ash. Silica is the basic foundation of the product, however. It is com-
mon for recycled glass (“cullet”) to be added to the mixture. The mixture is heated to approximately
1480–1570°C (2700–2850°F) and liquified.
The basic structural unit of silica has a tetrahedral shape with silicon in the center linked sym-
metrically to four oxygen atoms at its corners, giving the chemical formula SiO . Upon cooling
4
molten silica quickly, a randomly organized network of these tetrahedra are formed, linked at their
corners to give vitreous silica, an amorphous material (Pilkington, 2003):
1500°C
Na CO SiO 2 → Na SiO CO 2(g) (6.1)
3
3
2
2
Na SO 4
2
Na SiO xSiO 2 → (Na O)(SiO ) (6.2)
2 (x 1)
2
3
2
digestion
Soda ash makes the silica melt at a lower temperature. The sodium–oxygen atoms enter the sili-
con–oxygen network. Limestone imparts strength to the glass. Calcium enters the network structure
rendering it more complex so that during the cooling process, it is more difficult for the atoms to
arrange themselves for crystallization to occur.