Decolorization, azo dyes

Khehra MS, Saini HS, Sharma DK, Chadha BS, Chimni SS (2005) Comparative studies on potential of consortium and constituent pure bacterial isolates to decolorize azo dyes. Wat Res 39 5135-5141... 

Guo J, Zhou J, Wang D, Tian C, Wang Ping M, Uddin S (2008) A novel moderately halophilic bacterium for decolorizing azo dye under high salt condition. Biodegr 19 15-19... 

Nitrate and oxygen also may play an important role in determining the rate of azo dyes reduction. Wuhrmann et al. demonstrated that obligate aerobes might actually decolorize azo dye compounds under temporary anoxic conditions. However, high nitrite concentrations in the mixed liquor of activated sludge plants could significantly inhibit dye removal. 

Table 1 Selected white rot fungi and their enzymes able to decolorize azo dyes...

Extracellular peroxidases are produced by Streptomyces chromofuscus, with the capability to decolorize azo dyes associated to ligninolytic activity in aerobiosis. Azo dyes are converted to cationic radicals, which are subjected to nucleophilic attack by water or hydrogen peroxide molecules, producing reactive compounds that undergo redox reactions that result in a more stable intermediate [37]. 

Whereas non-azo dyes are almost resistant to bacterial decolorization, azo dyes can be decolorized by bacteria under anaerobic conditions to form aromatic amines which show both toxic and carcinogenic potential [18]. Further aerobic mineralization can therefore only be initiated by additional chemical oxidation, for example, by partial ozonation, as reported by Krull et al. [19]. 

Although it has been reported (138) that decolorization of wastewater containing reactive azo dyes with sodium hydrosulfite is possible only to a limited extent, others have demonstrated good reduction (decolorization). For example, using zinc hydrosulfite for the decolorization of dyed paper stock (139) resulted in color reduction of 98% for azo direct dyes (139). A Japanese patent (140) describes reducing an azo reactive dye such as Reactive Yellow 3 with sodium hydrosulfite into its respective aromatic amines which ate more readily adsorbable on carbon than the dye itself. This report has been confirmed with azo acid, direct, and reactive dyes (22). 

Chen H, Xu H, Heinze TM (2009) Decolorization of water and oil-soluble azo dyes by Lactobacillus acidophilis fermentum. J Ind Microbiol Biotechnol 36 1459-1466... 

Ozen AS, Aviyente V, Tezcanli-Guyer G, Ince NH (2005) Experimental and modeling approach to decolorization of azo dyes by ultrasound degradation of the hydrazone tautomer. J Phys Chem A 109 3506-3516... 

Various industrial sectors related to textiles, paper, and photography use dyes of synthetic origin with a complex aromatic molecular structure, which are frequently discharged in industrial effluents. One solution to these environmental problems is to use oxidative enzymes that destroy colored compounds and that may be of practical interest for the decolorization of synthetic dyes. Enzymes such as LiPX and MnPX are involved in the decolorization of synthetic azo dyes, such as Acid Orange II. 

Pseudomonas luteola Reactive azo dyes, Direct azo dyes and leather dyes The 59-99% color removal after 2-6 days static incubation, at dye concentration of 100 mg L 1, monoazo dyes showing fastest rate of decoloration [78]... 

Acid Orange 7 and many other dyes Bacterial consortium TJ-1 consisting of Aeromonas caviae, Proteus mirabilis, and Rhodococcus globerulus Decolorization of Acid Orange 7 was significantly higher with the consortium as compared to the individual strains. More than 90% decolorization could be achieved even at 200 mg L 1 within 16 h. The consortium also decolorized 15 other azo dyes individually as well as a simulated wastewater containing a mixture of all the 16 azo dyes [58]... 

BAA) and azo dyes bacterial culture under anaerobic conditions. The BAA could significantly increase the decolorization of one of the test dye by the salt-tolerant bacteria ... 

Orange II and other azo dyes Biodigester sludge from municipal waste plant augmented with sulfate reducing consortium The dye was decolorized by 95% within 24 h. Several other dyes including Reactive Black 5 and Reactive Red 120 and mixture of dyes were successfully degraded T[185]... 

Reactive Black 5 and Direct Brown 2 Granulated anaerobic sludge mixed culture Decolorization and substrate removal were achieved under test conditions but ultimate removal of azo dyes and substrate were not observed at high dye concentrations. Aromatic amine and volatile fatty acid accumulation observed proportionally at higher azo dye concentration [135]... 

Table 5 Rate of azo dye decolorization by different microbial strains...

Bromley-Challenor KCA, Knapp JS, Zhang Z et al (2000) Decolorization of an azo dye by unacclimated activated sludge under anaerobic conditions. Wat Res 34 4410-4418... 

Manu B, Chauhari S (2003) Decolorization of indigo and azo dyes in semicontinuous reactors with long hydraulic retention time. Process Biochem 38 1213-1221... 

Khalid A, Arshad M, Crowley DE (2008) Accelerated decolorization of structurally different azo dyes by newly isolated bacterial strains. Appl Microbiol Biotechnol 78 361-369... 

Khehra MS, Saini HS, Sharma DK et al (2005) Decolorization of various azo dyes by bacterial consortia. Dyes Pigm 67 55-61... 

Pandey A, Singh P, Iyengar L (2007) Bacterial decolorization and degradation of azo dyes. Int Biodeter Biodegr 59 73-84... 

Deng D, Guo J, Zeng G, Sun G (2008) Decolorization of anthraquinone, triphenyl-methane and azo dyes by a new isolated Bacillus cereus strain DC11. Int Biodeter Biodegr 62 263-269... 

Chang JS, Kuo TS, Chao YP, Ho JY, Lin PJ (2000) Azo dye decolorization with a mutant Escherichia coli strain. Biotechnol Lett 22 807-812... 

Isik M, Sponza DT (2003) Effect of oxygen on decolorization of azo dyes by Escherichia coli and Pseudomonas sp. and fate of aromatic amines. Process Biochem 38 1183-1192... 

Liu G, Zhou J, Wang J (2009) Acceleration of azo dye decolorization by using quinone reductase activity of azoreductase and quinone redox mediator. Bioresour Technol 100 2791-2795... 

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