9 An Insight into Microbial Remediation of Hexavalent Chromium …
217
et al. 2009). It is also reported that most of the microbial cultures are very much
suitable for the removal of lower concentration (1–100 mgL
−1 ) of Cr
6+ , while high
Cr
6+ concentration inhibits the microbial growth rate, disrupts the cell structure, and
ultimately reduces the biomass of microbial culture (Stasinakis et al. 2004; Narayani
and Shetty 2013).
9.5 Application of Mixed Cultured Bioreactors
Though Cr
6+ is very toxic, it inhibits the growth of microbial cells, damages the cells,
and affects the metabolic activities of microbes, and studies revealed that, there are
both living and dead cells able to adsorb Cr
6+ ions (Gokcay and Yetis 1991). It
is difficult to maintain laboratory conditions for the pure culture so the biological
treatment of Cr
6+ using single microbial species is not feasible at large scale (Narayani
and Shetty 2013). Dermou et al. (2005) used a pilot-scale biological reactor inoculated
with indigenous microbial consortia. They operated bioreactors in three-mode; batch,
continuous and sequencing batch reactor (SBR) with recirculation while the SBRrecirculation process was found to be more efficient in Cr
6+ removal than the former.
According to Katiyar and Katiyar (1997), cell immobilizations are much-advanced
method to reduce/biosorb Cr
6+ as compared to free cell culture. Immobilized cells are
more stable, high biomass loaded and can be regenerated easily, reusable, and they do
not require a continuous nutrient supply for growth. It can be easily separable from
water and does not cause clogging problems in a continuous flow system. Because of
the above reasons, the bed and mixed bed cultured bioreactors are proven to be more
effectice and widely advocated by scientific academia. Thus, bioreactors consisting
Cr
6+ reducing bacteria are cost-effective, easy, secure, and techno-feasible process
for Cr
6+ removal from water (Ganguli and Tripathi 2002).
Immobilized materials like alginate-carboxymethyl cellulose, rubber wood sawdust, calcium alginate, bed of PVC, granular activated carbon, agar layer on the
surface of the synthetic membrane, gravel, elemental sulfur, glass beads, wood husk,
and activated carbon have been used to support biofilms of chromium reducing bacteria (Xu et al. 2011; Kathiravan et al. 2010b; Benazir et al. 2010; Yang et al. 2009).
Farag and Zaki (2010) supported that, immobilized and mixed cultured cells can
be reused at least three times, without losing their Cr
6+ reducing efficiency. The
concept of reusing depends on the microbial species. Some microbial species cannot
reused as they are prone to cell lysis. The neverending academic search for more and
more effective and reusable microbial species is a scientific enigma and has spiked
the interest of researchers worldwide.
Figure 9.2 shows the suppose process for microbial remediation of Cr
6+ contaminated water. It is clear from the schematic diagram, prior to installation in industries,
laboratory trials are very much important to understand the applicability of microbes
toward Cr6+ removal from contaminated water. Isolations of microbial cells from
the Cr
6+ contaminated waste would save the acclimatization time and also may prove
more efficient than the same microbial strain isolated from non-contaminated sites.
217
et al. 2009). It is also reported that most of the microbial cultures are very much
suitable for the removal of lower concentration (1–100 mgL
−1 ) of Cr
6+ , while high
Cr
6+ concentration inhibits the microbial growth rate, disrupts the cell structure, and
ultimately reduces the biomass of microbial culture (Stasinakis et al. 2004; Narayani
and Shetty 2013).
9.5 Application of Mixed Cultured Bioreactors
Though Cr
6+ is very toxic, it inhibits the growth of microbial cells, damages the cells,
and affects the metabolic activities of microbes, and studies revealed that, there are
both living and dead cells able to adsorb Cr
6+ ions (Gokcay and Yetis 1991). It
is difficult to maintain laboratory conditions for the pure culture so the biological
treatment of Cr
6+ using single microbial species is not feasible at large scale (Narayani
and Shetty 2013). Dermou et al. (2005) used a pilot-scale biological reactor inoculated
with indigenous microbial consortia. They operated bioreactors in three-mode; batch,
continuous and sequencing batch reactor (SBR) with recirculation while the SBRrecirculation process was found to be more efficient in Cr
6+ removal than the former.
According to Katiyar and Katiyar (1997), cell immobilizations are much-advanced
method to reduce/biosorb Cr
6+ as compared to free cell culture. Immobilized cells are
more stable, high biomass loaded and can be regenerated easily, reusable, and they do
not require a continuous nutrient supply for growth. It can be easily separable from
water and does not cause clogging problems in a continuous flow system. Because of
the above reasons, the bed and mixed bed cultured bioreactors are proven to be more
effectice and widely advocated by scientific academia. Thus, bioreactors consisting
Cr
6+ reducing bacteria are cost-effective, easy, secure, and techno-feasible process
for Cr
6+ removal from water (Ganguli and Tripathi 2002).
Immobilized materials like alginate-carboxymethyl cellulose, rubber wood sawdust, calcium alginate, bed of PVC, granular activated carbon, agar layer on the
surface of the synthetic membrane, gravel, elemental sulfur, glass beads, wood husk,
and activated carbon have been used to support biofilms of chromium reducing bacteria (Xu et al. 2011; Kathiravan et al. 2010b; Benazir et al. 2010; Yang et al. 2009).
Farag and Zaki (2010) supported that, immobilized and mixed cultured cells can
be reused at least three times, without losing their Cr
6+ reducing efficiency. The
concept of reusing depends on the microbial species. Some microbial species cannot
reused as they are prone to cell lysis. The neverending academic search for more and
more effective and reusable microbial species is a scientific enigma and has spiked
the interest of researchers worldwide.
Figure 9.2 shows the suppose process for microbial remediation of Cr
6+ contaminated water. It is clear from the schematic diagram, prior to installation in industries,
laboratory trials are very much important to understand the applicability of microbes
toward Cr6+ removal from contaminated water. Isolations of microbial cells from
the Cr
6+ contaminated waste would save the acclimatization time and also may prove
more efficient than the same microbial strain isolated from non-contaminated sites.