The fate of azo dyes in aerobic microbial degradation systems: C.I. Acid Orange 7 and C.I. Acid Red 151

Azo dyes have been manufactured throughout the world for more than 120 years, and have been shown to be prevalent environmental contaminants. Recent estimates suggest greater than 15% of total world production of dyes, over 128 tons per day, are released into the environment through industrial discharges and improper waste disposal practices. The primary significance to human health of azo dyes is the carcinogenic potential of aromatic amines which arise as by-products during their manufacture, or as degradation products from reductive cleavage of the azo linkage in the environment via anaerobic microbial processes. The focus of this dissertation was to develop analytical methodologies to assess aerobic microbial degradation of azo dyes, as represented by C.I. Acid Orange 7 (AO7) and C.I. Acid Red 151 (AR151), in terms of metabolism of the dyes to innocuous products. Assessment was accomplished by an analytical approach involving the isolation, identification and quantitation of metabolites. The first step was to develop methods to first confirm the prevalence of dyestuffs in wastewaters at the Cincinnati Metropolitan Sewer District Mill Creek Treatment Facility and to evaluate these as a source of dye acclimated organisms for biodegradation studies. Following the inoculation of laboratory scale aerobic bioreactors, analytical and organic chemistry methodologies were developed to achieve the quantitative and qualitative identification of azo dyes and dye metabolites. These studies included chemical derivitization techniques which were used to simulate metabolism of dyes yielding products analogous to those observed from microbial metabolism, and to facilitate the acquisition of various spectroscopic data. Such information aided in the qualitative identification of unknown compounds.; The results of this dissertation research established the analytical methods developed and utilized during this investigation have general applicability to studies of dyes and related compounds in various matrices, and are suitable for use with biodegradation studies of other compounds. Data from this investigation suggest that azo bonds can be biochemically cleaved via processes yielding metabolites other than aromatic amines. In cases where azo bond cleavage lead to aromatic amines, the product isolated indicated that aerobic microbial systems investigated were found to further metabolize these potentially toxic intermediates to innocuous metabolic endpoints. This work has contributed to the understanding of the fate of representative azo dyes in aerobic microbial biodegradation systems, and has provided analytical techniques which can be utilized in further investigations. Consequently, the detoxification of azo dyes is accomplished by aerobic biodegradation processes, and through further research and technologic developments this approach can significantly impact the ultimate goal of remediation of hazardous wastes in man's environment.