Granite Processing Industry Wastewater Treatment
ARTHUR J. CONDREN, Assistant Professor
Department of Civil Engineering
University of Vermont
Burlington, Vermont
WILLIAM C. WALKER, Engineer
Dubois & King Consulting Engineers
Randolph, Vermont
INTRODUCTION
The leading mineral industry in Vermont is the granite processing industry. Prior to
the major depression of the I930's, the industry was widely dispersed throughout the State,
but at present better than 95 percent of the individual companies and supporting services
are located within a ten-mile radius of the Barre-Montpelier area. Within this area, there are
approximately 75 firms engaged in the various processing steps which result in a liquid
waste discharge.
The steps involved in producing granite monumental headstones, which is the main
product of the industry, are as follows: 1) Quarrying; 2) Sawing; 3) Rough finishing; 4)
Polishing; and 5) Decorating and/or lettering.
Quarrying, decorating and lettering produce little or no liquid waste. The remaining
steps, however, produce varying quantities of water polluted with granite particles and
processing materials such as carborundum, steel shot and tin oxide.
Granite blocks roughly 5 x 5 x 15 ft are brought from the quarry and are first sawed into
slabs varying in thickness from 3 to 16 inches. This sawing is normally done by using wire
saws, although the old practice of gang sawing is still used in a few plants.Carborundum (90-
mesh) is used as the actual cutting agent in this process. Considerable recirculation of the
process water is practiced to obtain maximum use of the carborundum. Fresh water and
carborundum are added to the system on a continuous basis to prevent the cutting "mud"
from becoming too concentrated and thus ineffective.
After sawing, the stones are rough finished. Saw marks on the large flat surfaces are
removed by grinding with 130-mesh carborundum. Curved and narrow width surfaces are
rough finished by high speed grinding with a tungsten carbide wheel roughly 18 inches in
diameter and 6 inches thick. Recirculation of process water is used extensively in the large
surface grinding process but not all in the "planing" operation used for the narrow widths
and curved surfaces.
Polishing is accomplished by buffing with tin oxide and various commercial
preparations. The major water use in this operation is periodic wash-down of the stone
during the polishing operation. Another process, known in the industry as "steeling", is also
performed on the polishing machines. This process uses small steel shot as the polishing
agent. Steeling produces a coarse white finish on the stone which is used to obtain a contrast
effect on the finished surfaces. No process water recirculation is practiced in the steeling
operation because the used mud darkens the stone.
It had been the custom of the granite processing industry to convey all of its process
wastewaters to the nearest receiving stream for ultimate disposal. In recent years, with the
institution of pollution abatement requirements, these process wastewaters had to be
subjected to primary sedimentation prior to discharge to a receiving waterway. In nearly all
cases, lagoons were constructed to comply with this requirement. A survey of the effluents
from 67 lagoons conducted by the Vermont Department of Water Resources in 1968
yielded the following results:
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