REMOVAL OF AZO DYES BY THE ACTIVATED SLUDGE PROCESS
Glenn M. Shaul, General Research Engineer
Clyde R. Dempsey, Environmental Engineer
Kenneth A. Dostal, Environmental Engineer
Industrial Wastes and Toxics Technology Division
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
INTRODUCTION
The Water Engineering Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency is conducting research designed to develop techniques for predicting
the fate of azo dyes in typical wastewater treatment systems which are treating wastewater contaminated with azo dyes. These techniques are being developed for EPA Office of Toxic Substance's use
in the Premanufacture Notification review process under section 5 of the Toxic Substances Control
Act and potentially in the regulation of hazardous chemical substances and mixtures under TSCA
section 6. A part of this research involves pilot plant investigations on the removal of azo dyes by
the activated sludge process. Generally, azo dyes contain between one and four azo linkages (-N
= N —), linking phenyl and naphthyl radicals that are usually substituted with some combination of
functional groups including: amino (-NH2), chloro (-C1), hydroxy (-OH), methyl (-CH3), nitro
( —N02) and sulfonic acid, sodium salt ( —SO,Na). Azo dyes are of concern to OTS because some
of the dyes, dye precursors or their degradation products such as aromatic amines, which are also
dye precursors, have been shown to be, or are suspected to be, carcinogenic [1]. Therefore, the principle objective of this research project will be to determine the fate of the dye compounds in the
activated sludge treatment process.
The results from this research are needed by OTS to aid in predicting the degree to which new
azo dyes and/or their degradation products pass through the activated sludge process. This research
will, hopefully, lead to the development of a predictive model of dye compound behavior based upon
chemical structure, physical properties and/or dye classification. This report presents background
information and results to date (5/85) for this ongoing project which is being performed at the EPA's
Test and Evaluation Facility in Cincinnati, Ohio.
LITERATURE REVIEW
Limited work on aerobic biological treatment systems has been done regarding the fate of specific
dye compounds in industrial or industrial/municipal wastewaters. Most of the research on aerobic
systems has utilized synthetic wastewater which allows use of simplified analytical methodology, but
this does not represent the variability inherent in actual wastewaters. However, much of what has
been done is still useful in predicting the fate of specific compounds in these treatment systems.
Straley [2] in his review of the literature stated that, "... dyes are generally recalcitrant to
biodegradation since one of the important factors in selecting a dye is its resistance to oxidation."
Some researchers [3,4,5] have shown that azo dyes can be slowly biodegraded. However, the primary
removal mechanism of dyes from wastewater treated by activated sludge seems to be adsorption onto
biological sludge solids [6]. Hitz et al. [7] reported that adsorption of dyes depends on the class of
dye and the structural differences within the classes. Hitz made the following general conclusions
based on limited aerobic jar tests with biological solids:
Acid dyes: poorly adsorbed, dependent on the number of SO,H groups.
Reactive dyes: very little adsorption.
Direct dyes: high adsorption.
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