Removal of Color from Sulfate Pulp
Wash Liquors
NELSON F. MURPHY, Professor of Chemical Engineering
DALE R. GREGORY, Graduate Assistant
Virginia Polytechnic Institute
Black_burg, Virginia
INTRODUCTION
Large quantities of water are used by the paper industry in cooking, washing,
and bleaching wood fibers resulting in the production of large volumes of highly
colored wastes. The water used in these operations is usually obtained from a
natural stream near the plant site and normally is returned to this stream following plant use.
Major effects of this waste disposal method are the increase in biological
oxygen demand and the discolorization of the stream. Reduction of biological
oxygen demand has been investigated extensively and successful reduction methods have been developed (1), but these treatments have negligible effect on color
reduction of these wastes. Although the color has little effect on aquatic life, except for reduction of ultra violet light reaching the biological constituents, their
reduction is desirable from an aesthetic view-point.
Several efforts made at Virginia Polytechnic Institute to remove the coloring
materials from the caustic wash of chlorine bleached kraft pulp (a typical, highly
colored, low-solids pulp mill waste) include super-chlorination (2), use of various
coagulants (3), alum treatment (4), and pilot plant settling and dewatering (5).
None of these efforts resulted in a color reduction method acceptable for commercial development.
This report describes the results obtained in the investigation ofthe combined
effects of temperature and pressure under different pH conditions on the waste de-
colorization.
PURPOSE OF INVESTIGATION
The purpose of this investigation was to determine the effects of temperature,
pressure, and pH on the decolorization of the caustic wash of chlorine bleached
kraft pulp obtained from the West Virginia Pulp and Paper Company, Covington,
Virginia.
LITERATURE REVIEW
The literature review for this investigation was limited primarily to a study
of the previous local attempts to decolorize the caustic wash liquor from sulfate
pulp. A preliminary search of the literature for waste decolorization and treatment method patents was also undertaken.
The following sections contain brief discussions of the several efforts made
in earlier studies to remove the colored materials from the caustic wash of chlorine bleached kraft pulp: (1) super-chlorination; (2) use of adsorbents; (3) alum
treatment and use of coagulants and flocculating aids; and, (4) pilot plant settling
and dewatering.
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