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Decolorization of
Semichemical Bleaching Wastes
DON E. BLOODGOOD,   Professor
Sanitary Engineering
Purdue University
Lafayette,  Indiana
A. SAMI EL-NAGGAR, Assistant Professor
Sanitary Engineering
Valparaiso University
Valparaiso, Indiana
The magnitude of the color problem in industrial wastes has always been
looked upon with concern. Public opinion and the increased emphasis on
stream pollution abatement has led to considerable research towards the elimination of color from wastes disposed of by dilution in surface waters. Indeed,
the color producing bodies in an industrial waste may have but little effect on
the biochemical load of the stream, but one only needs to know the public
dismay that arises from a colored stream even if the stream has little BOD and
considerable dissolved oxygen, DO.
Semi-chemical bleaching wastes are the kind of wastes that present a
color problem, and it is the purpose of this paper to present the investigation
carried out to remove the color of these wastes by the use of active carbon.
These wastes are produced from the bleaching process of semi-chemical pulp.
The pulp, after the initial cooking, is conveyed to the bleaching plant. The
pulp is first treated with chlorine water, then taken to a caustic extraction
stage where it is brought in contact with mild sodium hydroxide solution. The
final stage is a hypochlorite wash, where the pulp is washed in a solution of
calcium hypochlorite as a final polishing process. The typical process at any
commercial balancing plant includes these basic steps but may vary in respect
to the number of stages employed.
Three types of wastes are produced in the bleaching process. The first is
the acid waste from the chlorine stage; the second is the alkaline waste from
the caustic extraction stage; and the third is the hypochlorite waste from the
final bleaching stage. The work presented in this paper has been done using
the wastes from the first two stages, namely the acid and caustic bleaching
wastes from the Watervliet Paper Co., Watervliet, Michigan. Several samples
were received during the course of this study. The first samples were received
on June 8, 1959, the second on June 18, 1960 and the third on August29, 1960.
Each of the samples was shipped in a 15-gal polyethelene lined steel drum.
The analyses of the acid and caustic semichemical bleaching wastes,
used in this study, were performed at Purdue University and presented in the
report of February 6, 1960 (1). As a result of these analyses, it was found that
lignin in the wastes constituted the major part of the dissolved volatile solids
and probably was the major contributor to the color in the wastes. This statement is also supported by the information in the literature (2), (3), (4). Accordingly, it was decided to express the units of color in the waste in terms of
mg/1 as lignin.
A review of literature reveals that considerable work is being done in an
effort to treat the bleaching wastes. Previous research by the National Council
for  Stream Improvement and by several paper  mills has  shown that the
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