As the toxicity of nanoparticles for microorganisms is well documented in
literature (Li et al. 2010; Diao and Yao 2009), the dosage of nanoparticles in
integrated system plays a significant role. In case of CAH treatment by nZVI and
ORB, nZVI showed lethal effect on bacteria over 0.5 g/L, but it was found to have
positive impact on ORB activity below 0.1 g/L (Koenig et al. 2016). The issues of
nanoparticle toxicity toward bioagent can be addressed by modifying the surface of
nanoparticles through coating, stabilization, or entrapment. The coating prevents
the adhesion of nanoparticles on microbial cells, which in turn result in enhanced
remediation of contaminants. Li et al. (2010) compared bactericidal effect of bare
nZVI with polyelectrolyte (polystyrene sulfonate and polyaspartate) and natural
organic matter adsorbed nZVI on E. coli and found that surface modification
diminishes the toxicity of nZVI for exposure concentrations below 0.1–0.5 g/L.
The study reported that surface modification diminishes the toxicity of nZVI for
exposure concentrations below 0.1–0.5 g/L. An et al. (2010) while investigating
nitrate reduction with bimetallic nanoparticles and chitosan/sodium oleate modified iron nanoparticles also observed reduced toxicity of modified nanoparticles
toward microbes. The oxidation of nanoparticles with time or aging of
nanoparticles is also reported to decrease the toxicity of nanoparticles (Phenrat
et al. 2009). Apart from preventing the direct contact of nanoparticle with microbial cell, coating is also observed to enhance the expression of dechlorinating
genes in Dehalococcoides spp., which in turn accelerates the degradation efficiency of TCE in sequential nano-bio treatment system Xiu et al. (2010a).
Le et al. (2015) investigated polychlorinated biphenyls (PCBs) removal by the
nano-bio approach and found that the sequential treatment of PCB with Pd/Fe
nanoparticles followed by bioremediation with B. xenovorans could effectively
transform PCBs to less toxic and innocuous compounds. They further investigated
the toxicity level of PCBs in Escherichia coli DH5α before and after treatment using
toxic equivalent values and reported lower cytotoxicity of residual PCBs toward E.
coli after treatment. When nZVI and whey both were injected into groundwater
contaminated with Cr (VI), Němeček et al. (2016) observed 97–99% of Cr
(VI) removal in an integrated system having nZVI and whey generated microbes.
Besides removing the contaminants, microbes were also found to regenerate the
oxidized Fe
0 nanoparticles which further increased the rate of remediation reducing
the dosage of nanoparticles.
Multi-walled carbon nanotubes (CNTs) along with bioremediation are also successfully used for contaminant removal. In a study, Shewanella oneidensis MR-1, a
facultative Gram-negative bacterium, was immobilized in calcium alginate beads
containing carbon nanotubes to reduce Cr (VI) to Cr (III) in wastewater. The study
demonstrated four times higher reduction rates in cells immobilized over CNTs
containing beads in comparison to the free cells and the beads without CNTs (Yan
et al. 2013). The reason for enhanced reduction was ascribed to enhanced electron
transfer by the CNTs. Similarly, Pang et al. (2011) immobilized P. aeruginosa in
polyvinyl alcohol (PVA), sodium alginate, and CNTs matrix for carrying out Cr
(VI) reduction. The study showed that CNT-modified immobilized cells reduce Cr
(VI) contaminant more efficiently and can be reused effectively up to nine times.
7 Nano-bioremediation: An Innovative Remediation Technology for Treatment. . .
173
literature (Li et al. 2010; Diao and Yao 2009), the dosage of nanoparticles in
integrated system plays a significant role. In case of CAH treatment by nZVI and
ORB, nZVI showed lethal effect on bacteria over 0.5 g/L, but it was found to have
positive impact on ORB activity below 0.1 g/L (Koenig et al. 2016). The issues of
nanoparticle toxicity toward bioagent can be addressed by modifying the surface of
nanoparticles through coating, stabilization, or entrapment. The coating prevents
the adhesion of nanoparticles on microbial cells, which in turn result in enhanced
remediation of contaminants. Li et al. (2010) compared bactericidal effect of bare
nZVI with polyelectrolyte (polystyrene sulfonate and polyaspartate) and natural
organic matter adsorbed nZVI on E. coli and found that surface modification
diminishes the toxicity of nZVI for exposure concentrations below 0.1–0.5 g/L.
The study reported that surface modification diminishes the toxicity of nZVI for
exposure concentrations below 0.1–0.5 g/L. An et al. (2010) while investigating
nitrate reduction with bimetallic nanoparticles and chitosan/sodium oleate modified iron nanoparticles also observed reduced toxicity of modified nanoparticles
toward microbes. The oxidation of nanoparticles with time or aging of
nanoparticles is also reported to decrease the toxicity of nanoparticles (Phenrat
et al. 2009). Apart from preventing the direct contact of nanoparticle with microbial cell, coating is also observed to enhance the expression of dechlorinating
genes in Dehalococcoides spp., which in turn accelerates the degradation efficiency of TCE in sequential nano-bio treatment system Xiu et al. (2010a).
Le et al. (2015) investigated polychlorinated biphenyls (PCBs) removal by the
nano-bio approach and found that the sequential treatment of PCB with Pd/Fe
nanoparticles followed by bioremediation with B. xenovorans could effectively
transform PCBs to less toxic and innocuous compounds. They further investigated
the toxicity level of PCBs in Escherichia coli DH5α before and after treatment using
toxic equivalent values and reported lower cytotoxicity of residual PCBs toward E.
coli after treatment. When nZVI and whey both were injected into groundwater
contaminated with Cr (VI), Němeček et al. (2016) observed 97–99% of Cr
(VI) removal in an integrated system having nZVI and whey generated microbes.
Besides removing the contaminants, microbes were also found to regenerate the
oxidized Fe
0 nanoparticles which further increased the rate of remediation reducing
the dosage of nanoparticles.
Multi-walled carbon nanotubes (CNTs) along with bioremediation are also successfully used for contaminant removal. In a study, Shewanella oneidensis MR-1, a
facultative Gram-negative bacterium, was immobilized in calcium alginate beads
containing carbon nanotubes to reduce Cr (VI) to Cr (III) in wastewater. The study
demonstrated four times higher reduction rates in cells immobilized over CNTs
containing beads in comparison to the free cells and the beads without CNTs (Yan
et al. 2013). The reason for enhanced reduction was ascribed to enhanced electron
transfer by the CNTs. Similarly, Pang et al. (2011) immobilized P. aeruginosa in
polyvinyl alcohol (PVA), sodium alginate, and CNTs matrix for carrying out Cr
(VI) reduction. The study showed that CNT-modified immobilized cells reduce Cr
(VI) contaminant more efficiently and can be reused effectively up to nine times.
7 Nano-bioremediation: An Innovative Remediation Technology for Treatment. . .
173