Use of Fungal Laccases and Peroxidases for Enzymatic Treatment of Wastewater Containing Synthetic Dyes - Green Chemistry for Dyes Removal from Wastewater - page 233

Palmieri et al. [154] used P. ostreatus and its two laccase isozymes to
study the decolorization of Reactive Blue 19. They found that one of the
two isozymes (POXA3) was six-fold more efficient than the other isozyme
(POXC) in Reactive Blue 19 oxidation and decolorization. Contrary to other
researchers' reports (e.g., [149,155]), Palmieri et al. noted lesser importance
of peroxidases in the decolorization of Reactive Blue 19 by P. o s t r e a t u s . Hou
et al. [156] also found laccase as the only ligninolytic enzyme in the culture
of P. ostreatus (strain 32) and used the purified enzyme for the decoloriza-
tion of Reactive Blue 19. They used 0.16% ABTS (Figure 6.14) as a redox
mediator. Faraco et al. [157] also used P. ostreatus laccase for the treatment
of three model dye-containing wastewaters containing direct dyes, reactive
dyes, and acid dyes. The P. ostreatus laccase could not decolorize direct or
reactive dye mixtures, but acid dye model wastewater was decolorized up
to 35%. They found that an azo dye, Acid Yellow 49, was resistant to lac-
case decolorization, while an anthraquinone dye, Acid Blue 62, was rapidly
decolorized. The absence of phenolic hydroxyl or aniline amino group in
Acid Yellow 49 (see Figure 6.2) was suspected to be the reason for its resis-
tance toward the laccase-catalyzed decolorization.
Murugesan et al. [158] isolated and purified laccase from P. s a j o r - c a j u
and used the purified enzyme for decolorization of three azo dyes, includ-
ing Acid Red 18 (mono-azo), Acid Black 1 (diazo), and Direct Blue 71
(triazo). The laccase form P. s a j o r - c a j u could effectively decolorize all
the dyes without any addition of redox mediators. Acid Red 18 and Acid
Black 1 could be decolorized faster than Direct Blue 71, suggesting that
the structural complexity of Direct Blue 71 makes it more resistant to the
enzymatic treatment. Involvement of the phenolic group in the laccase-
catalyzed reactions is also suggested. Murugestan et al. [159] employed the
response surface methodology to investigate the decolorization of another
diazo dye Reactive Black 5 using purified P. s a j o r - c a j u laccase. Addition of
1-hydroxybenzotriazole (HBT; see Figure 6.14) as a redox mediator sig-
nificantly improved the decolorization of this diazo dye.
Wong and Yu [160] studied the decolorization of Acid Green 27
(anthraquinone), Acid Violet 7 (azo), and Acid Blue 74 (indigoid) using
purified T. versicolor laccase using ABTS as a redox mediator. They found
the importance of this mediator for the degradation of non-substrate dyes.
The low molecular weight fraction of the T. versicolor culture filtrate could
also mediate the dye decolorization. Nyanhongo et al. [161] screened
four ligninolytic fungi, T. modesta , T. versicolor , T. hir s ut a , and S. rolfsii ,
for the production of laccase and found that Trametes modesta was the
promising laccase producer. Two anthraquinone (Reactive Blue 19 and
Acid Blue 225), two triarylmethane (Acid Violet 17 and Basic Red 9), two