adsorb these pollutants, including bacterial, fungi, algae, yeast, industrial waste, and
agricultural waste; therefore, biosorption finds more attraction in industrial use.
4.4 Bio-oxidation/Bioreduction
Bio-oxidation/bioreduction and bioleaching processes are the two main categories of
biomining process. Bioreduction is the process in which a reduction of metal ions to
the lower redox state takes place and is responsible for the detoxification process. In
bioreduction, removal of pollutants can be achieved either by oxidation or reduction
reactions (Siddique et al. 2012). The detoxification mechanism involved in
the bioreduction process is not clear. The information available in the literature
regarding eukaryotic cells and yeast cells related to bioreduction is limited, and its
exact mechanism is not known yet. The type of mechanism, such as enzymatic or
nonenzymatic and intracellular or extracellular, responsible for the removal of metal
dyes is not known completely.
Microorganism participates in the oxidation reactions change the valence of
pollutants present in the effluents and thereby enhances mobility and reduces the
toxic effect of the pollutants. Bio-oxidation studies reported that microorganisms could reduce the valence of mercury from Hg
2À to easily evaporated Hg
0 by
aerobic bacteria; water-soluble and toxic chromium can be reduced from Cr
6À to less
toxic and water-insoluble Cr
3À by the Corynebacterium (Chanmugathas and Bollag
1988; Marchenko et al. 2015).
4.5 Bioleaching
Bioleaching is the process in which pollutants are removed from the contaminant
source by microorganisms. Bioleaching is also defined as an alteration of solid
pollutants into water-soluble forms with the help of microorganisms. Pollutant
solubility in the microorganism stains is the key factor in bioleaching. In contrast
to bioleaching, immobilized bioremediation methods such as biosorption,
bioaccumulation, and precipitation methods involve the transformation of pollutants
into an insoluble form.
In the bioleaching process, metal dye ions are mobilized from contaminated soil
or effluents by biological dissolution and complexation mechanisms. Secretions
resulted from the microbial metabolism are responsible for the bioleaching process.
Low-molecular-weight organic acids (such as oxalic acid, citric acid, etc.) produced
by the microorganisms can dissolve heavy metal dye ions and other pollutants
present in the contaminant site. It is reported in the literature that pollutants concentrate on solid waste through sorption, ion exchange, or complexation reactions.
However, in acidic environments, most metals show high mobility, and it was
reported that fungi could predominantly influence the solubility of metals under
9 Removal of Dyes From Industrial Effluents Using Bioremediation Technique
185
agricultural waste; therefore, biosorption finds more attraction in industrial use.
4.4 Bio-oxidation/Bioreduction
Bio-oxidation/bioreduction and bioleaching processes are the two main categories of
biomining process. Bioreduction is the process in which a reduction of metal ions to
the lower redox state takes place and is responsible for the detoxification process. In
bioreduction, removal of pollutants can be achieved either by oxidation or reduction
reactions (Siddique et al. 2012). The detoxification mechanism involved in
the bioreduction process is not clear. The information available in the literature
regarding eukaryotic cells and yeast cells related to bioreduction is limited, and its
exact mechanism is not known yet. The type of mechanism, such as enzymatic or
nonenzymatic and intracellular or extracellular, responsible for the removal of metal
dyes is not known completely.
Microorganism participates in the oxidation reactions change the valence of
pollutants present in the effluents and thereby enhances mobility and reduces the
toxic effect of the pollutants. Bio-oxidation studies reported that microorganisms could reduce the valence of mercury from Hg
2À to easily evaporated Hg
0 by
aerobic bacteria; water-soluble and toxic chromium can be reduced from Cr
6À to less
toxic and water-insoluble Cr
3À by the Corynebacterium (Chanmugathas and Bollag
1988; Marchenko et al. 2015).
4.5 Bioleaching
Bioleaching is the process in which pollutants are removed from the contaminant
source by microorganisms. Bioleaching is also defined as an alteration of solid
pollutants into water-soluble forms with the help of microorganisms. Pollutant
solubility in the microorganism stains is the key factor in bioleaching. In contrast
to bioleaching, immobilized bioremediation methods such as biosorption,
bioaccumulation, and precipitation methods involve the transformation of pollutants
into an insoluble form.
In the bioleaching process, metal dye ions are mobilized from contaminated soil
or effluents by biological dissolution and complexation mechanisms. Secretions
resulted from the microbial metabolism are responsible for the bioleaching process.
Low-molecular-weight organic acids (such as oxalic acid, citric acid, etc.) produced
by the microorganisms can dissolve heavy metal dye ions and other pollutants
present in the contaminant site. It is reported in the literature that pollutants concentrate on solid waste through sorption, ion exchange, or complexation reactions.
However, in acidic environments, most metals show high mobility, and it was
reported that fungi could predominantly influence the solubility of metals under
9 Removal of Dyes From Industrial Effluents Using Bioremediation Technique
185