choice if MEOR is considered in the extraction process. For instance, guar gum
polymer is used to improve oil recovery by fracturing the bedrock. However, after
the fracturing, it is necessary to reduce the polymer viscosity to ease the oil flow.
Reduction in viscosity of the guar gum can be achieved by using mannanases which
degrade the polymer. Since the polymer flooding is alkaline, the wells are alkaline,
and, hence, it is imperative to use mannanases that are operationally stable at alkaline
condition, and such enzymes have been engineered specifically for this
application [267].
4.13 Alkaliphiles in Environmental Biotechnology
Microbial cells and their enzymes have been playing crucial roles in waste management. Hazardous substances in effluents, often from industries, are degraded or
biotransformed into harmless products by microorganisms. Moreover, microbes
decrease the biological oxygen demand (BOD) and chemical oxygen demand
(COD) of effluents which in turn allows easy disposal after treatment. For such
applications, the pH of the effluent (waste) dictates which kind of microbes or
enzymes to be considered for treatment. If the effluent is alkaline, the use of
alkaliphiles or alkaline active enzymes is a primary choice. The other option is
neutralization of the effluent and treatment with neutralophiles or their enzymes
which are often optimally active around neutrality. However, the later choice is timeconsuming and cost-incurring and may also increase the salinity which is an
environmental concern. On the other hand, direct use of alkaliphiles or their enzymes
is attractive to treat alkaline effluents due to its time-saving, technical, economic, and
environmental benefits.
There are some that show cases where alkaliphiles or alkaline active enzymes are
implemented in treating waste. Azo dyes which are widely used in many industries
are hazardous and need to be removed from effluents. One of such dyes is Reactive
Orange 16. This dye has been removed in a cost-effective way using the alkaliphilic
microbe Bacillus flexus VITSP6 at pH 11, which is able to biotransform the toxic dye
to harmless low molecular products [268]. Similarly, the degradation of toxic azo
dyes by the alkaliphilic bacteria Nocardiopsis alba [269], Bacillus cohnii MTCC
3616 [270], and consortium [271] has been reported.
Alkaline active enzymes are considered to treat nitroaromatic compounds. These
substances are among the most common industrial chemicals that are currently in use
and have become one of the major classes of pollutants. Nitroaromatics are highly
toxic and mutagenic [272, 273], and, hence, waste containing these pollutants should
be treated effectively. Although microbial degradation has been tried widely
[274, 275], little is done on the use of isolated enzymes on detoxification of
nitroaromatics. However, some enzymes of alkaliphilic origin have been tried
successfully. The alkaliphile Bacillus badius flavin-free NADH azoreductase is
used for biotransformation and detoxification of nitroaromatic compounds such as
1-chloro-2-nitrobenzene, 3-nitrobenzoic acid, 3-nitrotoluene, and 4-nitrotoluene
34
G. Mamo and B. Mattiasson
polymer is used to improve oil recovery by fracturing the bedrock. However, after
the fracturing, it is necessary to reduce the polymer viscosity to ease the oil flow.
Reduction in viscosity of the guar gum can be achieved by using mannanases which
degrade the polymer. Since the polymer flooding is alkaline, the wells are alkaline,
and, hence, it is imperative to use mannanases that are operationally stable at alkaline
condition, and such enzymes have been engineered specifically for this
application [267].
4.13 Alkaliphiles in Environmental Biotechnology
Microbial cells and their enzymes have been playing crucial roles in waste management. Hazardous substances in effluents, often from industries, are degraded or
biotransformed into harmless products by microorganisms. Moreover, microbes
decrease the biological oxygen demand (BOD) and chemical oxygen demand
(COD) of effluents which in turn allows easy disposal after treatment. For such
applications, the pH of the effluent (waste) dictates which kind of microbes or
enzymes to be considered for treatment. If the effluent is alkaline, the use of
alkaliphiles or alkaline active enzymes is a primary choice. The other option is
neutralization of the effluent and treatment with neutralophiles or their enzymes
which are often optimally active around neutrality. However, the later choice is timeconsuming and cost-incurring and may also increase the salinity which is an
environmental concern. On the other hand, direct use of alkaliphiles or their enzymes
is attractive to treat alkaline effluents due to its time-saving, technical, economic, and
environmental benefits.
There are some that show cases where alkaliphiles or alkaline active enzymes are
implemented in treating waste. Azo dyes which are widely used in many industries
are hazardous and need to be removed from effluents. One of such dyes is Reactive
Orange 16. This dye has been removed in a cost-effective way using the alkaliphilic
microbe Bacillus flexus VITSP6 at pH 11, which is able to biotransform the toxic dye
to harmless low molecular products [268]. Similarly, the degradation of toxic azo
dyes by the alkaliphilic bacteria Nocardiopsis alba [269], Bacillus cohnii MTCC
3616 [270], and consortium [271] has been reported.
Alkaline active enzymes are considered to treat nitroaromatic compounds. These
substances are among the most common industrial chemicals that are currently in use
and have become one of the major classes of pollutants. Nitroaromatics are highly
toxic and mutagenic [272, 273], and, hence, waste containing these pollutants should
be treated effectively. Although microbial degradation has been tried widely
[274, 275], little is done on the use of isolated enzymes on detoxification of
nitroaromatics. However, some enzymes of alkaliphilic origin have been tried
successfully. The alkaliphile Bacillus badius flavin-free NADH azoreductase is
used for biotransformation and detoxification of nitroaromatic compounds such as
1-chloro-2-nitrobenzene, 3-nitrobenzoic acid, 3-nitrotoluene, and 4-nitrotoluene
34
G. Mamo and B. Mattiasson