Textile Dye Wastes
NELSON   L.   NEMEROW
Assistant Professor of  Sanitary Engineering
North Carolina State College
Raleigh, North Carolina
The pollutional character of textile dye wastes depends upon the
type of dye used, which in turn depends to a great extent upon what
kind of cloth is being dyed and the specifications of the finished dyed
cloth. The main dyes are (1) Direct colors (2) Sulphur colors
(3) Vat colors (4) Acid colors (5) Developed colors (6) Naphthanol
colors  (7)  Acetate colors.
Direct dyes are very commonly used because the colors are water
soluble and can be applied directly to cotton, often with the aid of
10-40 per cent sodium chloride or Glauber's salt based on the weight
of goods being dyed. These dyes are mainly azo dyes, derivatives of
benzidin or tolidin. The amount of dye used varies with the color
and intensity; it varies from 0.1 to 8 per cent of the weight of the
goods dyed. In a few instances common salt is also added in the last
rinse before drying to increase the retention of dye in the fiber. The
major portion of the solids then are mainly inorganic salts even though
they are highly colored due to the small quantity of very soluble
dyestuff. In addition to the dyestuff and salt, oils of various sorts are
used by some mills. These oils act to reduce the surface tension
between the water and the cotton and make the latter more absorbent.
In spite of the varying practices that produce different quantities
of wastes the pollution contributed from machines accommodating
definite amounts of cotton is about the same regardless of the volume
of the combined wastes wherever the waste values are expressed in
pounds per 100 pounds of goods.
Direct dyes are mostly used in vegetable fibers, such as cotton and
rayon. The wastes, containing a large amount of common salt, when
in a large volume and not strongly diluted by sewage, may be corrosive
to metallic equipment in sewage treatment plants.
Sulphur dyes are so-called because they consist of sulphur compounds
and are dyed as a rule with the addition of sodium sulfide and common
salt to the bath. The chemical nature of the sulphur dyes is still more
or less undetermined, but it is probable that they consist of a mixture
of complicated organic derivatives, in which sulphur appears to be a
constituent part.    The principal   sulphur colors  are  blacks,  browns,
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