described the pneumatic and direct injection as two different delivery methods of
EnZVI, providing promising results relating to the dechlorination and reductive
dechlorination of chlorinated ethenes. Extensive tests by O’Hara et al. (2006)
revealed the synergetic removal effect of EnZVI, while the combination of sequestration and abiotic degradation mechanisms driven by the oil emulsion and nZVI,
respectively, was found. Moreover, there have been promising results relating to the
stability and targetability of nZVI (Sheu et al. 2015). Dong et al. (2015) showed that
nZVI in emulsion appears to form fewer aggregates in comparison with bare nZVI,
while the oil concentration can be optimized, which leads to an efficient and longterm reactivity toward toxic compounds removal. Furthermore, in a pilot-scale study
where a nZVI-emulsified colloidal substrate was used for PCE degradation, Sheu
et al. (2016) not only observed the efficient dechlorination after 130 days of
operation, but also noticed that the use of the nZVI-emulsified colloidal substrate
increased the popolutation of Dehalococcoides spp. (DHC) and Desulfitobacterium
spp. (DSB). The increase of DHC and DSB population promotes the PCE dechlorination process (Grostern and Edwards 2006). It has to be noted that there are some
challenges that have to be dealt with in relation to the injection of such particles to a
subsurface, e.g., due to the viscosity of these emulsions (Bhattacharjee and Ghoshal
2016). The type of surfactant and the concentrations of all the components, e.g., oil,
could be tuned in order to maintain the highest remediation performance. For
instance, it was found that ionic surfactants are more preferable than nonionic
surfactants since they can lead, to some extent, to the enhancement of the degradation ability of nZVI (Cook 2009).
2.3.4 Using Electrokinetics
Electrokinetic (EK) remediation technology has been applied successfully to many
pilot-scale sites for soil and underwater treatment of various organic and inorganic
contaminants (Virkutyte et al. 2002; Gomes et al. 2012). An electrokinetic system
includes a pair of electrodes and direct-current power imbedded in the soil. A low
intensity electric current passes between a cathode and an anode. In that way,
different ions, charged particles, and water are moving towards the opposite charged
electrode. Mechanisms such as electro-migration, electro-osmosis, electrophoresis,
and electrolysis take place (Mulligan et al. 2001; Weng et al. 2006). The contaminants and their byproducts can be collected by electroplating or precipitation/coprecipitation at the electrodesby the generated H 2 and OH
À . In Fig. 2.9a are depicted
the electrokinetic phenomena that can occur involving the movement of electricity,
charged particles and fluids.
The integration of both techniques, electrokinetics and nZVI, can couple the
advantages and increase the benefits regarding water remediation. Among the
overall reactions that occur during the application of the electrokinetics, electrolysis
reaction of water causes the creation of H
+ and OH
À ions, with the first one to be
more mobile. The protons (H
+
) are very beneficial to the reaction with ferrous ions
2 Nanoscale Zero-Valent Iron Particles for Water Treatment: From Basic. . .
35
EnZVI, providing promising results relating to the dechlorination and reductive
dechlorination of chlorinated ethenes. Extensive tests by O’Hara et al. (2006)
revealed the synergetic removal effect of EnZVI, while the combination of sequestration and abiotic degradation mechanisms driven by the oil emulsion and nZVI,
respectively, was found. Moreover, there have been promising results relating to the
stability and targetability of nZVI (Sheu et al. 2015). Dong et al. (2015) showed that
nZVI in emulsion appears to form fewer aggregates in comparison with bare nZVI,
while the oil concentration can be optimized, which leads to an efficient and longterm reactivity toward toxic compounds removal. Furthermore, in a pilot-scale study
where a nZVI-emulsified colloidal substrate was used for PCE degradation, Sheu
et al. (2016) not only observed the efficient dechlorination after 130 days of
operation, but also noticed that the use of the nZVI-emulsified colloidal substrate
increased the popolutation of Dehalococcoides spp. (DHC) and Desulfitobacterium
spp. (DSB). The increase of DHC and DSB population promotes the PCE dechlorination process (Grostern and Edwards 2006). It has to be noted that there are some
challenges that have to be dealt with in relation to the injection of such particles to a
subsurface, e.g., due to the viscosity of these emulsions (Bhattacharjee and Ghoshal
2016). The type of surfactant and the concentrations of all the components, e.g., oil,
could be tuned in order to maintain the highest remediation performance. For
instance, it was found that ionic surfactants are more preferable than nonionic
surfactants since they can lead, to some extent, to the enhancement of the degradation ability of nZVI (Cook 2009).
2.3.4 Using Electrokinetics
Electrokinetic (EK) remediation technology has been applied successfully to many
pilot-scale sites for soil and underwater treatment of various organic and inorganic
contaminants (Virkutyte et al. 2002; Gomes et al. 2012). An electrokinetic system
includes a pair of electrodes and direct-current power imbedded in the soil. A low
intensity electric current passes between a cathode and an anode. In that way,
different ions, charged particles, and water are moving towards the opposite charged
electrode. Mechanisms such as electro-migration, electro-osmosis, electrophoresis,
and electrolysis take place (Mulligan et al. 2001; Weng et al. 2006). The contaminants and their byproducts can be collected by electroplating or precipitation/coprecipitation at the electrodesby the generated H 2 and OH
À . In Fig. 2.9a are depicted
the electrokinetic phenomena that can occur involving the movement of electricity,
charged particles and fluids.
The integration of both techniques, electrokinetics and nZVI, can couple the
advantages and increase the benefits regarding water remediation. Among the
overall reactions that occur during the application of the electrokinetics, electrolysis
reaction of water causes the creation of H
+ and OH
À ions, with the first one to be
more mobile. The protons (H
+
) are very beneficial to the reaction with ferrous ions
2 Nanoscale Zero-Valent Iron Particles for Water Treatment: From Basic. . .
35