acidic conditions (Gadd 1993). Gadd (1993) proved that microbial interaction with
metal pollutants is significant in both natural and synthetic environments in altering
the physical and chemical states of the pollutants. He further reported that the
biochemical activity of fungi and other microorganisms significantly influences the
mobility characteristics and modifies the biogeochemical cycles. Acydolysis and
complexolysis were reported to be important reactions responsible for the solubilization of metal dyes. Metabolites having metal-complexing properties such as
phenolic compounds and organic acids are also found to be involved in metal
solubilization processes. Organic acids having low molecular weight are found to
be good leaching agents. It was reported in the literature that low-molecular-weight
organic acids provide protons required for solubilization process and metal chelating
anion to participate in the metal complexation reaction with the metal cations.
Organic acids are useful in two ways: first, they acidify the substrate which in turn
enhances the mobility characteristics of metal ions, and the second one is they form
complex reaction responsible for the solubility of metal ions (Gadd 1999; 2004).
Bioleaching process also depends on the nutrient availability; studies showed that
bioleaching rate significantly improved with nutrient uptake. Some microorganisms
such as Citrobacter may also form insoluble phosphate coat on the cell surface that
can entrap dye pollutants during bioleaching.
4.6 Bioaugmentation
Bioaugmentation is the process of adding specific pure microbial strains or mixed
strains to the contaminated sites for the removal of pollutants. Added microorganisms alter the physicochemical characteristics of the pollutants and detoxify the site.
Indigenous microorganism, i.e., microorganisms already present in the contaminated
site, may not be available in sufficient quantity or may not be efficient in removing
mixed pollutants; hence, adding additional amounts of the required type of microorganisms enhances the detoxification process (Leahy and Colwell 1990; Herrero
and Stuckey 2015). Studies on the application of various bacteria, yeast, and fungi in
bioaugmentation of dyes were conducted worldwide. Studies conducted on microorganisms such as C. fabianii, C. tropicalis, and Candida digboiensis in the
bioaugmentation of pollutant removal showed the efficiency of these microorganisms in pollutant removal from the site. It is reported that the application of mixed
microbial cultures rather than the pure cultures is more efficient in bioaugmentation
process. Addition of mixed microbial cultures follows different metabolic pathways
and creates suitable environments required for bioremediation of pollutants (He et al.
2014).
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N. S. KV
metal pollutants is significant in both natural and synthetic environments in altering
the physical and chemical states of the pollutants. He further reported that the
biochemical activity of fungi and other microorganisms significantly influences the
mobility characteristics and modifies the biogeochemical cycles. Acydolysis and
complexolysis were reported to be important reactions responsible for the solubilization of metal dyes. Metabolites having metal-complexing properties such as
phenolic compounds and organic acids are also found to be involved in metal
solubilization processes. Organic acids having low molecular weight are found to
be good leaching agents. It was reported in the literature that low-molecular-weight
organic acids provide protons required for solubilization process and metal chelating
anion to participate in the metal complexation reaction with the metal cations.
Organic acids are useful in two ways: first, they acidify the substrate which in turn
enhances the mobility characteristics of metal ions, and the second one is they form
complex reaction responsible for the solubility of metal ions (Gadd 1999; 2004).
Bioleaching process also depends on the nutrient availability; studies showed that
bioleaching rate significantly improved with nutrient uptake. Some microorganisms
such as Citrobacter may also form insoluble phosphate coat on the cell surface that
can entrap dye pollutants during bioleaching.
4.6 Bioaugmentation
Bioaugmentation is the process of adding specific pure microbial strains or mixed
strains to the contaminated sites for the removal of pollutants. Added microorganisms alter the physicochemical characteristics of the pollutants and detoxify the site.
Indigenous microorganism, i.e., microorganisms already present in the contaminated
site, may not be available in sufficient quantity or may not be efficient in removing
mixed pollutants; hence, adding additional amounts of the required type of microorganisms enhances the detoxification process (Leahy and Colwell 1990; Herrero
and Stuckey 2015). Studies on the application of various bacteria, yeast, and fungi in
bioaugmentation of dyes were conducted worldwide. Studies conducted on microorganisms such as C. fabianii, C. tropicalis, and Candida digboiensis in the
bioaugmentation of pollutant removal showed the efficiency of these microorganisms in pollutant removal from the site. It is reported that the application of mixed
microbial cultures rather than the pure cultures is more efficient in bioaugmentation
process. Addition of mixed microbial cultures follows different metabolic pathways
and creates suitable environments required for bioremediation of pollutants (He et al.
2014).
186
N. S. KV