Application of Extremophilic Microorganisms in Decolorization and Biodegradation of Textile Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 277

remediation. Heavy metals are one of the most important environmental concerns,
as their accumulation through food chain can cause serious health problems. Some
halophilic microorganisms have been reported with the ability to remediate heavy
metal pollution through absorption. Hence, they can be used as biological agents for
removal of heavy metals from highly saline industrial wastewaters (Popescu and
Dumitru 2009 ; Francis et al. 2000 ; Amoozegar et al. 2012 ). Exploring extremo-
philic microbial potential for bioremediation purposes will result in using organisms
that have a high tolerance to the environmental harsh conditions of salinity and high
temperature for in situ and ex situ remediation in bioreactors (Kumar et al. 2011 ).

6 Extremophilic Microorganisms and Textile Dyes

In discriminate release of colored wastewater into the environment has become
today a serious ecological obstacle. Therefore, green practices are tried to assort a
proper decolorization or degradation approaches for the colored industrial ef uents

before releasing them to the environment. Extremophilic microorganisms are one of
the most attractive biological tools for bioremediation in the harsh condition of
most ef

uents. Factors, like pH, temperature, salinity, and dye concentration have a
great effect on dye removal by microorganisms.
In most cases, sodium concentrations above 3,000 ppm moderately inhibit most
of microbial activities except for halotolerant and halophilic microbes which can
tolerate or may require salt to be active (Anjaneya et al. 2011 ). Halophilic micro-
organisms can be found in hypersaline environment which are widely distributed
around the world. These microorganisms are a group of extremophiles which not
only cope with salinity as an environmental extreme (Oren 2011 ), but also sub-
jected to other kinds of extreme conditions, like high pH values, high or low
temperature, low oxygen availability, pressure, heavy metals and/ or other toxic
compounds (Oren 2002 ). Based on optimal growth with respect to the NaCl con-
centration, halophilic microorganisms fall into two physiological groups which
include extreme halophiles (optimal growth at 2.5

5.2 M NaCl) and moderate

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halophiles (optimal growth at 0.5 2.5 M NaCl). Besides, there are some non-

halophilic microorganisms with optimal growth in medium with less than 0.2 M
NaCl concentration, but also they are able to tolerate high concentration of NaCl
and hence de

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ned as halotolerant microbes (Kushsner and Kamekura 1988 ).
In textile dyeing process, different salts are used for different purposes which
include separating organic contaminants, inducing dyestuff precipitation, and
mixing with concentrated dyes to standardize them. Addition of sodium hydroxide
into dye bath to increase the pH could be another reason for elevated Sodium level
(Khalid et al. 2008a ). High salt concentration could decrease the decolorization
process because of inability of microorganism to be active in this condition.
Therefore, halophilic and halotolerant microorganisms can be only useful in this
respect.