Factors Affecting the Complete Mineralization of Azo Dyes

3 Factors Affecting the Complete Mineralization of Azo Dyes 3.1 Oxygen Availability 

Redox mediators, such as flavins or quinones, are usually involved in the azo bond reduction. Therefore, the azo bond cleavage is a chemical, unspecific reaction that can occur inside or outside the cell, relying on the redox potential of the redox mediators and of the azo compounds. Also the reduction of the redox mediators can be both a chemical and an enzymatic process. As a consequence, it is an evidence that environmental conditions can affect the azo dyes degradation process extent both directly, depending on the reductive or oxidative status of the environment, and indirectly, influencing the microbial metabolism. 

Anaerobiosis is the most studied environmental factor affecting this reaction. Under aerobic conditions, oxygen, and azo dyes are in competition for the reduced electron carriers. 

From the biological point of view, the effect of anaerobiosis has been characterized in purely anaerobic, facultative anaerobic, and aerobic bacteria, in yeasts, and in tissues from higher organisms [6-12], From these studies it can be deduced that almost every azo compound can be biologically reduced under anaerobic conditions [4]. Reduced flavins are produced by cytosol flavin-dependent reductases [6, 13], while quinone reductase activity located in the plasma membrane [14] and extracellular azo reductase activities [9, 15] were also observed. 

The degradation of azo dyes in aerobiosis can also be carried out by lignindegrading fungi, mainly white-rot fungi, or by peroxidase-producing bacterial strain, mainly Streptomyces species, as extensively reviewed by Stolz [4]. 

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The last chapter highlights the factors affecting the complete mineralization of azo dyes. 

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