Methods for Recycling Glass From Industrial
and Municipal Solid Wastes
WARD R. MALISCH, Associate Professor
BOBBY G. WIXSON, Associate Professor
DELBERT E. DAY, Professor
University of Missouri-Rolla
Rolla, Missouri
JACK H. ABRAHAMS, JR.
Glass Container Manufacturers Institute
Washington, D.C.
INTRODUCTION
In 1970. solid wastes generated from municipal and industrial sources were estimated
at more than 360 million tons annually: this figure included 250 million tons of household,
commercial and municipal wastes and 110 million tons resulting from industrial activities
(I). Waste glass comprises approximately 6 to 12 percent of the mixed municipal refuse on a
dry weight basis (2) but estimates of the nature and quantities of industrial waste are few (3).
Based upon data from interviews with seven firms producing flat glass and pressed blown
glassware (4), the total scrap and waste produced in these industries in 1965 was estimated at
1.60 million tons. Of this quantity, 10 to 20 percent is combustible material and the non-
combustible portion includes not only scrap glass but also process waste, defective batch
material, and plaster and abrasives from trie polishing of glass. In the container industry,
the scrap glass is ground and returned to the batch, so that disposal by other means is not
necessary.
The principal raw materials for glass are plentiful and low in cost so that conservation
of natural materials is not a major incentive for recycling. However, recycling or reuse of
waste glass is desirable primarily because it reduces the volume of refuse to be disposed of by
conventional means such as landfill disposal, and because some cullet is beneficial in the
glass-making processes. Thus, several means for recycling are being investigated. Primary
recycling is accomplished by remelting the waste glass and using it in the manufacture of
new glass products while secondary uses include production of highway paving materials,
bricks, glass wool insulation or other structural products. The extent to which either of
these approaches is utilized will depend upon the characteristics of the waste glass and the
locality in which it is collected.
INDUSTRIAL PRIMARY RECYCLING
The addition of some amounts of salvaged glass (cullet) to basic raw materials has long
been used in the container industry to hasten the melting of the other ingredients in the glass
furnaces. Today, with many plants now using it at the 10 percent level and some already at
or above the 30 percent level, cullet is becoming a significant source of basic raw material.
The major portion of the cullet used in glass-making at present is derived from in-house
process waste and no waste glass from container manufacturing processes finds its way into
the solid waste stream. Scrap dealers who sell cullet to glass manufacturing plants obtain
their supplies from various commercial or industrial operations where relatively
homogeneous glass which has not been mixed with other refuse is available in quantity-
bottling plants, dairies, breweries, etc. Another source of cullet is the nearly 100 bottle
reclamation centers operated by Glass Container Manufacturers Institute member
companies in some 25 states. These salvaged bottles, now being reclaimed at a rate
approaching one billion per year, are being recycled back into the bottle-making process
(5). Bottles collected at these centers are color-sorted, with all metallics removed so that
they can be used with no further processing.
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