Application of Extremophilic Microorganisms in Decolorization and Biodegradation of Textile Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 265

textile ef uents to the environment HAS undesired impact on neighboring receptor

water bodies because of presence of toxic reactive dyes and dark coloration. Due to
environmental and health effects of dyes released in textile industry wastewater
made the textile wastewater decolorization a subject to scienti

c scrutiny (Christie

2007 ).
Textile dyeing industries are facing problems to meet the green practices stan-
dards for safe discharge of wastewater due to complex nature and hard-to-treat by
conventional methods. Therefore, in recent years, biological decolorization, using
microorganisms capable of decolorizing and detoxifying the synthetic dyes, has
been considered as a promising and environmentally benign method (McMullan
et al. 2001 ).

4 Microbial Degradation of Textile Dyes

Amongst different decolorization methods for textile wastewaters; the biological
methods seem to be most applicable. Bacteria, fungi and yeasts could be used based
on their ability to decolorize dyes in the wastewater through aerobic, anaerobic or
anaerobic/ aerobic systems. Among different techniques for wastewater decolor-
ization, the live or dead microbial biomass adsorption has a great signicance in
biorecovery of dyes after decolorization of the ef

uents (McMullan et al. 2001 ).
Some of microorganisms that are able to decolorize textile dyes, are of different
taxonomic groups and their ef ciency in dye removal has been summarized in

Table 3 . Some microbes show a very high ef ciency in waste water decolorization

which is attributed to their growth rate and versatile metabolism. However, harsh
condition of wastewater ef

uents poses a limiting factor for mesophilic microor-
ganisms to remediate the wastewaters properly. But the ability of extremophilic
microorganism to survive in such harsh condition has some advantages over other
mesophilic microorganisms for the bioremediation of colored wastewaters.

5 Extremophilic Microorganisms

Extremophiles are organisms that are adapted to grow optimally at or near to the
extreme ranges of environmental variables. Most of them thrive under conditions
that are clearly hostile from a human perspective. Extremophiles can fall in different
categories based on single environmental extreme they survive. Different categories
of extremophiles include acidophile, alkaliphile, endolith, halophile, hyperther-
mophile, hypolith, metallotolerant, oligotroph, piezophile, psychrophile, radiore-
sistant, thermophile, toxitolerant and xerophile (Horikoshi 2011 ). Besides, there
are many extremophiles which fall in two or more of above categories. They
represent the polyextremophiles which refer to microorganisms adapted to two
or more different environmental extremes (Rothschild and Mancinelli 2001 ).