are required to increase the productivity to reduce the
bioethanol price. The enhancement in hydrolytic activity of
microbes and inventing new suitable enzymes proficient for
enduring acute environments has become of primary
importance in several current reports.
In addition to this, a microbial fuel cell (MFC) device
transforms the chemical energy from biowaste (e.g.,
wastewater) into electrical energy using microbes as biocatalysts under anaerobic environments (Sobieszuk et al.
2017; Mansoorian et al. 2013; Angosto et al. 2015). In a
typical double (cathode and anode) compartment MFC,
microbes are present in the anodic cell and oxidize biowaste
(organic compounds) and produce electrons. The produced
energy is then stockpiled in adenosine triphosphate
(Sobieszuk et al. 2012). The generated protons from the
anaerobic respiration process are moved through the proton
permeable membrane to the cathode chamber and produce
water by reacting with oxygen and electrons (Oliveira et al.
2013). Usually, the performance of MFC is specified based
on obtained potential, which depends on the rate of the
biowaste redox process by the microbes, the circuit impedance, the proton transportation towards cathodic cells
through proton exchange membrane, reduction reactions at
the cathode, etc. (Mardanpour et al. 2017; Zeng et al. 2010).
A number of MFC configurations with different electrode
materials, compartment numbers, and microbes were used as
a biocatalyst (Hidalgo et al. 2015). Microbial fuel cells are
potential candidates for wastewater and sewage treatment
methods not only because of the producing electrical energy
from biowastes but also due to a considerable reduction in
the amount of sludge produced.
2.3.2 Enzymatic Bioconversion Process
After completion of pretreatment, polycarbohydrates (cellulose and hemicellulose) are hydrolyzed into soluble pentoses
and hexoses using various enzymes. Scientists have discovered specific microbes from various biosources, with the
perspective that those microbes would have an excellent
ability to bioconversion as special enzymes. In many
bioindustries, these enzymes act as biocatalysts to accomplish the reactions in an eco-friendly and economical method
as conflicting to the usage of chemical reagents. Based on
temperature, alkalinity, and acidity, the microbial enzymes
are classified as thermophilic, alkalophilic, acidophilic, etc.
A few enzymes with special characteristics are discussed as
follows.
Amylase
Amylase enzymes are the most significant biocatalysts, and
their main use in bioindustries is for starch-based conversion
methods (Nigam 2013). An alpha-amylase enzyme, known
to be endo-1, 4-a-D-glucan glucanohydrolase, randomly
cleavage the a-1,4 bonding of contiguous glucose moieties
in polycarbohydrates into small chain oligomeric sugars.
The amylolytic and corresponding enzymes are considered
as glycosidic hydrolases and were produced by a broad
range of microbes (Singh et al. 1995; Sivaramakrishnan et al.
2006) and classified into exo, endo, and cyclodextrin producing enzymes. Amyloglucosidase is an exoamylase
enzyme capable of breaking the a-1,4 bonding in starch to
produce monomers. This amyloglucosidase cleaves the a-1,6
glyosidic bonds with sluggish rates and releasing b-D glucose (James and Lee 1997); however, the process can be
efficient in an acidic environment and mild heat (Kumar and
Satyanarayana 2009). The primary applications of these
enzymes are in starch bio-liquefaction (for biofuels), sugar,
paper, pulp, baking, and pharmaceutical industries (Nigam
2013). These enzymes possess large-scale production capabilities, including the production of commercial maltose
syrup, glucose syrup, fructose corn syrups, decrease in turbidity to produce extended shelf-life for fruit juice, and
starch saccharification in the brewing industry (Nigam
2013).
Protease
Among all the commercially available enzymes, the microbial protease enzymes are widely studied by the researchers
(Vijayalakshmi et al. 2013; Mukherjee et al. 2008). In
general, these proteases were prepared from three microbial
environments which are alkaline, neutral, and acidic. Owing
to the extraordinary activity and constancy in atypical circumstances of thrilling biological constraints, the basic serine proteases possess major applications in the bioindustry
and are of specific attention being extra appropriate for a
variety of bioconversion functions. These alkaline proteases
show their ability to work even at a high pH range, elevated
temperatures, as well as in the existence of constraint
materials (Vijayalakshmi et al. 2013).
Ligninase or Laccase
Ligninase is a complex enzymatic system of three oxidative
enzymes of manganese peroxidase, lignin peroxidase, and
laccase. They are mainly used in bioconversion of lignocellulosic biowastes into monomers. Due to the combination
of synergistic enzymes, these are extremely adaptable and
are applied in a number of commercial progressions (Dahiya
et al. 1998). Ligninolytic enzymes are mainly used in the
pollution control system, bio-remediation process, and in the
treatment of industrial wastes (sewage) comprising intractable and lethal chemicals like phenols, cloth colorants, etc.
(Robinson and Nigam 2008).
Cellulose
Cellulose is the third most significant enzyme for the use of
bioindustries and mainly used for the generation of glucose
from cellulosic biowastes (Pandey et al. 1999). The primary
8
A. M. Palve et al.
bioethanol price. The enhancement in hydrolytic activity of
microbes and inventing new suitable enzymes proficient for
enduring acute environments has become of primary
importance in several current reports.
In addition to this, a microbial fuel cell (MFC) device
transforms the chemical energy from biowaste (e.g.,
wastewater) into electrical energy using microbes as biocatalysts under anaerobic environments (Sobieszuk et al.
2017; Mansoorian et al. 2013; Angosto et al. 2015). In a
typical double (cathode and anode) compartment MFC,
microbes are present in the anodic cell and oxidize biowaste
(organic compounds) and produce electrons. The produced
energy is then stockpiled in adenosine triphosphate
(Sobieszuk et al. 2012). The generated protons from the
anaerobic respiration process are moved through the proton
permeable membrane to the cathode chamber and produce
water by reacting with oxygen and electrons (Oliveira et al.
2013). Usually, the performance of MFC is specified based
on obtained potential, which depends on the rate of the
biowaste redox process by the microbes, the circuit impedance, the proton transportation towards cathodic cells
through proton exchange membrane, reduction reactions at
the cathode, etc. (Mardanpour et al. 2017; Zeng et al. 2010).
A number of MFC configurations with different electrode
materials, compartment numbers, and microbes were used as
a biocatalyst (Hidalgo et al. 2015). Microbial fuel cells are
potential candidates for wastewater and sewage treatment
methods not only because of the producing electrical energy
from biowastes but also due to a considerable reduction in
the amount of sludge produced.
2.3.2 Enzymatic Bioconversion Process
After completion of pretreatment, polycarbohydrates (cellulose and hemicellulose) are hydrolyzed into soluble pentoses
and hexoses using various enzymes. Scientists have discovered specific microbes from various biosources, with the
perspective that those microbes would have an excellent
ability to bioconversion as special enzymes. In many
bioindustries, these enzymes act as biocatalysts to accomplish the reactions in an eco-friendly and economical method
as conflicting to the usage of chemical reagents. Based on
temperature, alkalinity, and acidity, the microbial enzymes
are classified as thermophilic, alkalophilic, acidophilic, etc.
A few enzymes with special characteristics are discussed as
follows.
Amylase
Amylase enzymes are the most significant biocatalysts, and
their main use in bioindustries is for starch-based conversion
methods (Nigam 2013). An alpha-amylase enzyme, known
to be endo-1, 4-a-D-glucan glucanohydrolase, randomly
cleavage the a-1,4 bonding of contiguous glucose moieties
in polycarbohydrates into small chain oligomeric sugars.
The amylolytic and corresponding enzymes are considered
as glycosidic hydrolases and were produced by a broad
range of microbes (Singh et al. 1995; Sivaramakrishnan et al.
2006) and classified into exo, endo, and cyclodextrin producing enzymes. Amyloglucosidase is an exoamylase
enzyme capable of breaking the a-1,4 bonding in starch to
produce monomers. This amyloglucosidase cleaves the a-1,6
glyosidic bonds with sluggish rates and releasing b-D glucose (James and Lee 1997); however, the process can be
efficient in an acidic environment and mild heat (Kumar and
Satyanarayana 2009). The primary applications of these
enzymes are in starch bio-liquefaction (for biofuels), sugar,
paper, pulp, baking, and pharmaceutical industries (Nigam
2013). These enzymes possess large-scale production capabilities, including the production of commercial maltose
syrup, glucose syrup, fructose corn syrups, decrease in turbidity to produce extended shelf-life for fruit juice, and
starch saccharification in the brewing industry (Nigam
2013).
Protease
Among all the commercially available enzymes, the microbial protease enzymes are widely studied by the researchers
(Vijayalakshmi et al. 2013; Mukherjee et al. 2008). In
general, these proteases were prepared from three microbial
environments which are alkaline, neutral, and acidic. Owing
to the extraordinary activity and constancy in atypical circumstances of thrilling biological constraints, the basic serine proteases possess major applications in the bioindustry
and are of specific attention being extra appropriate for a
variety of bioconversion functions. These alkaline proteases
show their ability to work even at a high pH range, elevated
temperatures, as well as in the existence of constraint
materials (Vijayalakshmi et al. 2013).
Ligninase or Laccase
Ligninase is a complex enzymatic system of three oxidative
enzymes of manganese peroxidase, lignin peroxidase, and
laccase. They are mainly used in bioconversion of lignocellulosic biowastes into monomers. Due to the combination
of synergistic enzymes, these are extremely adaptable and
are applied in a number of commercial progressions (Dahiya
et al. 1998). Ligninolytic enzymes are mainly used in the
pollution control system, bio-remediation process, and in the
treatment of industrial wastes (sewage) comprising intractable and lethal chemicals like phenols, cloth colorants, etc.
(Robinson and Nigam 2008).
Cellulose
Cellulose is the third most significant enzyme for the use of
bioindustries and mainly used for the generation of glucose
from cellulosic biowastes (Pandey et al. 1999). The primary
8
A. M. Palve et al.