remediation results. For instance, incorporation of microbial strains in nZVI helps in
more efficient remediation of pollutants. Chlorinated aliphatic hydrocarbons (CAH)
are recalcitrant compounds which can neither be removed completely by nZVI nor
organochlorine respiring bacteria (ORB). Koenig et al. (2016) combined both the
technologies for removal of CAHs and showed that at appropriate dosage, a wide
range of CAHs can be treated efficiently. They further suggested that the spent nZVI
can be regenerated by certain minerals like cysteine and vitamins which remains
available in bacterial environments. A reductive-oxidative strategy consisting of
nZVI and an aerobic bacterium (Sphingomonas sp. PH-07) found to be effective
for degradation of polybrominated diphenyl ethers (PBDEs) in aqueous solution.
The nZVI particles break down the complex PBDEs like deca-BDE to lower BDEs
through reductive debromination which were then degraded easily by microbes
(Kim et al. 2012). Under optimal conditions, nZVI-CA beads showed 91.35% Cr
(VI) removal, and for biofilm-coated nZVI-CA beads, the removal percentage was
found to be 97.84%. When the efficiency of beads was investigated in column
experiments, increased Cr (VI) removal was observed as compared to the free
beads. The height of the column increases the reactive sites of the beads, which in
turn enhance the removal of the toxic metal from the contaminated water. However
in case of real samples, the efficiency of removal got decreased which may be
attributed to the presence of colloidal particles present in the samples (Ravikumar
et al. 2016). It is suggested by a report that permeable reactive Fe
0 barriers might be
an effective approach to degrade RDX plumes and that treatment efficiency could be
enhanced through bioaugmentation. When nZVI and white rot fungi were applied
simultaneously, a substantial increase in RDX degradation as compared to the
individual approach was observed. In addition to that, nZVI corrosion produces
hydrogen gas which favors the growth and metabolic activities of the fungi further
promoting RDX removal (Oh et al. 2001).
Hydrogen is considered as highly favorable electron donor for microorganisms
carrying out biotransformation of contaminants in environmental substrates. The
possibility of using cathodic hydrogen (produced during corrosion of nZVI under
anaerobic conditions) as an electron donor for contaminant-degrading microbes, has
been explored by many researchers (Weathers et al. 1997; Liu et al. 2005). Xiu et al.
(2010b) demonstrated that the degradation of chlorinated solvent can be boosted by
using nZVI as reducing agent along with bacteria that utilize cathodic depolarization
and reductive dechlorination as metabolic niches. In another study wherein
carboxymethyl cellulose (CMC) stabilized bimetallic nanoparticles (CMC-Pd/
nFe
0 ) was integrated with Sphingomonas sp. strain NM05 for studying degradation
of γ-HCH, synergistic effect on γ-HCH degradation was reported in case of integrated system, which further indicate that stabilized nanoparticles have some kind of
biostimulatory effect on cell growth (Singh et al. 2013). Shin and Cha (2008) also
observed biostimulatory effect of nFe
0 on nitrate reducing microbial culture. In
addition, nZVI supported microbial reduction was found to remain indifferent to
fluctuating low temperatures, which otherwise is a major disadvantage with abiotic
nitrate reduction.
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R. Singh et al.
more efficient remediation of pollutants. Chlorinated aliphatic hydrocarbons (CAH)
are recalcitrant compounds which can neither be removed completely by nZVI nor
organochlorine respiring bacteria (ORB). Koenig et al. (2016) combined both the
technologies for removal of CAHs and showed that at appropriate dosage, a wide
range of CAHs can be treated efficiently. They further suggested that the spent nZVI
can be regenerated by certain minerals like cysteine and vitamins which remains
available in bacterial environments. A reductive-oxidative strategy consisting of
nZVI and an aerobic bacterium (Sphingomonas sp. PH-07) found to be effective
for degradation of polybrominated diphenyl ethers (PBDEs) in aqueous solution.
The nZVI particles break down the complex PBDEs like deca-BDE to lower BDEs
through reductive debromination which were then degraded easily by microbes
(Kim et al. 2012). Under optimal conditions, nZVI-CA beads showed 91.35% Cr
(VI) removal, and for biofilm-coated nZVI-CA beads, the removal percentage was
found to be 97.84%. When the efficiency of beads was investigated in column
experiments, increased Cr (VI) removal was observed as compared to the free
beads. The height of the column increases the reactive sites of the beads, which in
turn enhance the removal of the toxic metal from the contaminated water. However
in case of real samples, the efficiency of removal got decreased which may be
attributed to the presence of colloidal particles present in the samples (Ravikumar
et al. 2016). It is suggested by a report that permeable reactive Fe
0 barriers might be
an effective approach to degrade RDX plumes and that treatment efficiency could be
enhanced through bioaugmentation. When nZVI and white rot fungi were applied
simultaneously, a substantial increase in RDX degradation as compared to the
individual approach was observed. In addition to that, nZVI corrosion produces
hydrogen gas which favors the growth and metabolic activities of the fungi further
promoting RDX removal (Oh et al. 2001).
Hydrogen is considered as highly favorable electron donor for microorganisms
carrying out biotransformation of contaminants in environmental substrates. The
possibility of using cathodic hydrogen (produced during corrosion of nZVI under
anaerobic conditions) as an electron donor for contaminant-degrading microbes, has
been explored by many researchers (Weathers et al. 1997; Liu et al. 2005). Xiu et al.
(2010b) demonstrated that the degradation of chlorinated solvent can be boosted by
using nZVI as reducing agent along with bacteria that utilize cathodic depolarization
and reductive dechlorination as metabolic niches. In another study wherein
carboxymethyl cellulose (CMC) stabilized bimetallic nanoparticles (CMC-Pd/
nFe
0 ) was integrated with Sphingomonas sp. strain NM05 for studying degradation
of γ-HCH, synergistic effect on γ-HCH degradation was reported in case of integrated system, which further indicate that stabilized nanoparticles have some kind of
biostimulatory effect on cell growth (Singh et al. 2013). Shin and Cha (2008) also
observed biostimulatory effect of nFe
0 on nitrate reducing microbial culture. In
addition, nZVI supported microbial reduction was found to remain indifferent to
fluctuating low temperatures, which otherwise is a major disadvantage with abiotic
nitrate reduction.
172
R. Singh et al.