Polymer Aided Alum Coagulation of Textile Dyeing
and Finishing Wastes
WILLIAM C. KREYE, Graduate Student
PAUL H. KING, Professor
CLIFFORD W. RANDALL, Associate Professor
Department of Sanitary Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
INTRODUCTION
The recent attention given by regulatory agencies to adverse aesthetic effects associated
with municipal and industrial wastewater discharges has brought about an accelerated
interest in the removal of color during treatment of a variety of industrial wastes. Among
the manufacturing operations most directly affected is the textile dyeing and finishing
industry. By far the most noticeable characteristic of both the raw wastewater and the
treated effluent from such establishments is color. Although biological treatment of these
wastewaters is usually effective in removing a large percentage of oxygen demanding
organic matter, biological treatment is frequently ineffective in removing color. For this
reason chemical treatment, primarily aimed at color removal, will be increasingly
applicable to the textile industry.
The purpose of the research described in this paper was to develop a chemical
treatment system using alum as primary coagulant, which would remove a high percentage
of the color causing compounds from a typical textile dyeing and finishing waste. Special
attention was given to the settleability and compaction of the sludge produced, because
such sludge presents a particularly difficult disposal problem. The use of various types of
organic polyelectrolytes as flocculant aids was also investigated. Although the basic
premise underlying this research is that chemical treatment is best for color removal while
biological treatment is best for reduction of organic matter, the removal of organic material
in chemical treatment was also monitored. Through this means the reduction of organic
load on a biological unit utilized following the chemical treatment facility may be evaluated.
PREVIOUS STUDIES
In spite of relatively high costs, chemical coagulation is the most widely used unit
process for achieving a high degree of color removal from textile dyeing and finishing
wastes. The literature contains numerous reports of specific studies utilizing such primary
coagulants as alum, various iron salts and lime. Summary papers discussing chemical
coagulation of textile wastes as well as other appropriate processes have been contributed
by Nemerow (I), Leatherland (2), and Souther (3).
More specific articles on chemical coagulation have indicated the relative merits of
various primary coagulants. Porges, et al (4), in a summary article concluded that, although
textile dye wastes vary widely, color can be removed from essentially all of them by chemical
coagulation. These investigators evaluated a number of coagulants and coagulant
combinations including alum, ferric chloride, ferrous sulfate, and lime. Optimum pH
ranges were defined and the influence of mixing and flocculation time as well as
temperature were noted. The selection of an appropriate coagulant was found to be waste
dependent. Alum was reported to produce a poorly settling floe. Souther and Alspaugh (5)
in a comprehensive study of color removal, showed the effect of a wide variety of coagulants
on process efficiency. Good color removal was achieved by chemical treatment, but costs
were high.
King and Randall (7) have reported on the use of the excess lime process for color
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