87    REMOVAL OF COLOR FROM DISTILLERY WASTEWATER
A. V. S. Prabhakara Rao, Professor
J. Karthikeyan, Research Scholar
Leela Iyengar, Senior Research Officer
Environmental Engineering Laboratory
Department of Civil Engineering
Indian Institute of Technology
Kanpur-208016 INDIA
INTRODUCTION
Color is a visible pollutant and its presence not only hampers the aesthetic quality of surface waters
but also affects and alters the aquatic ecosystem by reducing the penetration of sunlight, thus limiting
the photosynthetic activity. Many colored compounds are good chelating agents and thus keep some
heavy metals in solution. Recently, regulatory agencies are becoming more stringent in the discharge
of colored effluents to surface waters.
Distillery wastewaters originating from cane molasses based alcohol industry are distinct in having
very high BOD and dissolved solids, low pH and are dark brown in color. Colored substances in
distillery wastewaters can be traced back to molasses used for fermentation. Although anthocyanins
and tannins, which form intensely colored complexes with iron, are important, major contribution for
color in molasses is due to colored non-sugars formed by decomposition products and other chemical
reactions during processing. Alkaline pH during processing and high temperatures used for crystallization of sugar lead to the formation of caramels, melanoidins and a variety of sugar decomposition
products such as hydroxymethyl furfural, which in turn, polymerize to form yellow pigments. Colloidal nature of caramels and melanoidins have been reported.1 Electrophoretic separation and the
removal of part of colored pigments by anion exchange resins indicate that some of the pigments are
negatively charged.2,3 These colored pigments are sometimes referred to as "nonfermentable fraction"
of molasses as they remain even after yeast fermentation.4 However, other colorants can also be
formed during yeast growth and processing of alcohol, which find their way into distillery effluents.
Anaerobic biological treatment has been extensively used for the reduction of BOD and COD.59
Color removals in this process are not significant. Damodara Rao and Viraraghavan9 have reported
that brown color already present in spent wash intensified during anaerobic/aerobic treatment of
distillery wastewaters. Decolorization of molasses after yeast fermentation using sorbents, oxidizing
agents and microorganisms have also been reported.1<M4 Not much information is available on the use
of coagulants for color removal from molasses and distillery wastewaters, before and after anaerobic
biological treatment, using coagulants and oxidizing agents.
MATERIALS AND METHODS
All chemicals used were of reagent grade except for chlorine oxidation experiments, where commercially available bleaching powder with an active chlorine content of 27.2% was used. Cetyl pyridinium
chloride, supplied by Merck Chemicals, represented the quaternary ammonium compound.
Molasses and distillery effluents were obtained from local sugar and fermentation industries.
Experimental
Suitably diluted molasses and distillery wastewaters were fed to laboratory scale fixed film anaerobic digesters, where Raschig rings were used as supporting media for immobilizing microorganisms.
Characteristics of the influent for and the effluent from the digester are given in Table I. Influents are
designated as RM (raw molasses) and RDW (raw distillery wastewater), whereas effluents from the
digesters are termed as TM (treated molasses) and TDW (treated distillery wastewaters).
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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