Microbe-Mediated Degradation of Synthetic Dyes in Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 213

Fig. 4 Electron ow preference as a function of the different electron couples (Dubin and Wright
1975 ; Cervantes 2002 ; Madigan et al. 2003 ; Dos Santos 2005 ). RM and RM reduc are the oxidized
and the reduced forms of the redox mediator, respectively

Fig. 5 Schematic for indirect azo dye reduction. B and C are the biological and chemical steps,
respectively

electron donor (van der Zee et al. 2003 ). Unfortunately, the standard redox potential
(E

′ 0 ) for most of azo dyes is unknown, however, this information can be obtained
by using polarography. In a screening of redox potential values for different azo
dyes, it was found that E0 values are generally between -0.430 and -0.180 V (Dubin
and Wright 1975 ). Rau et al. ( 2002a , b ) stated that the NAD(P)H co-factor, which
had the lowest E 0.320 V, set the limits of redox mediators application.

The reason for this is that mediators with a more negative E0 value will not be
reduced by the cells, and mediators with E

′ 0 value of

−

′ 0 greater than − 0.05 V will not