Use of Fungal Laccases and Peroxidases for Enzymatic Treatment of Wastewater Containing Synthetic Dyes - Green Chemistry for Dyes Removal from Wastewater - page 247

The utility of LiP in synthetic dye decolorization appears to be limited
because of the lack of reliable sources of this enzyme and the require-
ment of veratryl alcohol as a cofactor and redox mediator for its catalytic
activity [110]. It is well known that the secretion of LiP is tightly regu-
lated by the physiological state of white rot fungi such as P. chrysosporium
and requires nitrogen-limited cultivation conditions for its production
[177,178]. In comparison, MnP is more promising because this enzyme
can be produced by many white rot fungi without strict physiological regu-
lations. The requirement of manganese ions and organic acids is a disad-
vantage of MnP, although these are less expensive than veratryl alcohol
and laccase-redox mediators. Manganese-independent fungal peroxidases,
including versatile peroxidase from P. eryngii and P. ostreatus and DyP from
B. adusta, should be investigated more in order to explore the potential
applications of these seemingly very useful enzymes for dye decolorization.
It should be noted that information about the characteristics of the deg-
radation byproducts and degradation mechanisms/pathways of enzyme-
catalyzed dye decolorization is still largely missing. The identity, toxicity,
and biodegradability of decolorized and degraded dye molecules are very
important for downstream treatment processes and effluent discharge.
Since the enzymatic treatment alone is not capable of mineralizing the
dye molecules, an additional treatment process would be needed if the
effluent from the enzymatic treatment has high organic matter content.
Combinations with different unit processes, such as aerobic/anaerobic
processes, ozonation, advanced oxidation processes, membrane processes,
should be evaluated to achieve optimum treatment. More research needs
to be done to explore the possibility of reusing the treated water for dye-
ing processes. In the literature reviewed in this chapter, only Abadulla
et al. [54] investigated the reuse potential of treated wastewater with a lim-
ited success.
It is evident that certain synthetic dyes are more susceptible to enzy-
matic decolorization than others. It is desirable to perform more compre-
hensive structure activity relationship studies to elucidate the degradation
mechanisms and to optimize the treatment. In addition, more research
is needed to investigate the applicability of this technology to real textile
wastewater treatment. One thing to note is that it appears that most of the
researchers, if not all, have used raw dye molecules in their decolorization
feasibility studies. However, some dye molecules, especially reactive dyes,
undergo a series of chemical reactions with other constituents during the
dyeing process as mentioned in Section 6.2.2. Therefore, hydrolyzed reac-
tive dyes should be used and tested, instead of the raw dye products.