Biodegradation of selected azo dyes under methanogenic conditions

Abstract

Biological treatment of wastewaters discharged by the textile industry could potentially be problematic due to the high toxicity and recalcitrance of the commonly-used azo dye compounds. In the present report, the fate of two azo dyes under methanogenic conditions was studied. Mordant Orange 1 (MO1) and Azodisalicylate (ADS) were completely reduced and decolorised in continuous UASB reactors in the presence of cosubstrates. In the MO1 reactor, both 5-aminosalicylic acid (5-ASA) and 1,4-phenylenediamine were identified as products of azo cleavage. After long adaptation periods, 5-ASA was detected at trace levels, indicating further mineralization. ADS, a pharmaceutical azo dye constructed from two 5-ASA units, was completely mineralized even in the absence of cosubstrate, indicating that the metabolism of 5-ASA could provide the reducing equivalents needed for the azo reduction. Batch experiments confirmed the ADS mineralization. These results demonstrate that some azo dyes could serve as a carbon, energy, and nitrogen source for anaerobic bacteria.

Effects of dye additives on the ozonation process and oxidation by-products: a comparative study using hydrolyzed C.I. Reactive Red 120

“…Reactive Red 120 (before ozonation) after 22 days incubation (Fig. 5) can be attributed to the adaptation of bacteria to recalcitrant azo dye substrate or so called cross-acclimatization [4]. Krull et al (1998) reported that the biomass used for the anoxic treatment of six different reactive azo dyes was growing in the following aerobic phase when readily biodegradable compounds were present [31].…”

“…A significant remainder of about 40-70% of COD and color in textile finishing industry effluents after conventional biological treatment requires an advanced treatment for improving the quality [3][4][5][6]. Commercial azo dyes used are mixtures of dyes including other additives such as intermediates produced during dye www.elsevier.com/locate/dyepig synthesis (e.g.…”

Microbial Populations Associated with Treatment of an Industrial Dye Effluent in an Anaerobic Baffled Reactor

“…Reduction of azo dyes has been shown to occur under anaerobic conditions, particularly in association with intestinal microorganisms (7,48). Several different mechanisms have been proposed for reduction or degradation of azo dyes and similar compounds.…”

“…Seshadri and coworkers proposed that biotransformation of azo dyes is a two-step process, in which the azo bond is reduced under anaerobic conditions, producing two aromatic amines, which are then mineralized by aerobic microorganisms (51). In contrast to this proposed process, subsequent research showed that in the presence of readily utilizable cosubstrates, two azo dyes were reduced and decolorized under methanogenic conditions (48), and breakdown products from one azo dye were further mineralized. Due to comparatively low operation costs, use of anaerobic digestion to treat dye wastewater is a cost-effective alternative to the physical and chemical methods commonly used to do this.…”

Anaerobic Microbial Associations Degrading Aminoaromatic Acids

“…Unlike sludge, which is highly specific to certain substrates [15], the enrichment cultures can degrade any of the target compounds without a lag, although at variable rates. The different rates of biodegradation of ABA and ASA isomers provide additional proof of the significance of the position of substituents in aromatic compounds for their mineralization by active microbial associations [10,12]. The rate of degradation by the associations remained high from cycle to cycle, not changing after passages.…”