Environmental Engineering Reference
In-Depth Information
Ni ranging between 2.5 and 20 wt%, and then decreased when the Ni loading was further
increased to 25 wt% (Figure 4.4e). In addition, the stability and longevity of the immobi-
lized Fe/Ni nanoparticles was evaluated by repeatedly injecting TCE into the solutions. A
rapid and complete dechlorination of TCE by trace amounts of Fe/Ni nanoparticles was
observed after 16 cycles of injection within 10 days (Figure 4.4f), indicating that the immo-
bilization of Fe/Ni nanoparticles in the hydrophilic nylon 66 membrane can retain the
longevity and high reactivity of nanoparticles toward TCE dechlorination.
4.8 Status of Field Application in the United States, Europe, and Taiwan
The application of nZVI on
in situ
groundwater remediation has been conducted in a vari-
ety of ields [149-152]. As of today, there are 58 completed or ongoing nZVI remediation
projects worldwide at a pilot or ield scale [152]. Among these, 36 remediation projects were
conducted in the United States, including eight full-scale implementation cases. Europe
is another fast-developing region where 17 sites, mainly located in the Czech Republic
and Germany, have been commissioned including three full-scale deployments [153]. In
Taiwan, three pilot scale tests have been implemented since 2006 (Figure 4.5) [154,155].
On the basis of the data collected from the ield demonstration, there seems to be no
simple guideline to ensure the success of nZVI remediation in the ield. The inal outcome
is largely dependent on the nature of treatment such as source removal or pathway man-
agement, site hydrogeological characteristics, and the maturity of nZVI technology. In
addition, the current understanding about the interaction between nZVI and the aquifer
environment is still limited. The geochemical properties of the aquifer may be changed by
nZVI amendment [27,153-157], while the mobility of nZVI is inluenced largely by the geo-
chemistry of aquifers. The irst impact of water geochemistry on the nZVI is likely to be the
particle stabilization. Bare nZVI readily forms an aggregate and becomes a larger particle
(usually microscale) in the absence of suitable stabilizers [158]. Polymeric stabilization using
a wide array of polymers such as PAA and CMC [159,160] is the most common way to stabi-
lize nZVI in the aquifer. However, the concentration of stabilizer applied to an nZVI slurry
drops naturally in the groundwater because of the dilution effect. The aggregation of nZVI
occurs after the injection, as has been observed by SEM images of the soil sample [154].
The transport of nanoparticles in the aquifer is a complicated process involving physio-
chemical and biological interactions [158,161]. The nZVI transport in the aquifer is largely
controlled by ionic strengths, pH and dissolved organic matter (e.g., fulvic acid and humic
acid), and groundwater hydrology such as hydraulic conductivity and porosity [158]. In
general, a decrease in ionic strength and an increase in dissolved organic matter concentra-
tion tend to favor the nZVI transport. The travel distance up to 3 m has been observed in
the ield studies within the sandy aquifer with high hydraulic conductivity [154]. Still, there
are many uncertainties associated with the application of nZVI in the ield, including the
extent of nZVI migration laterally and vertically, the changes in reactivity due to passiv-
ation by groundwater constituents, and the change of microbial activities. To minimize this
uncertainty, a detailed and accurate site assessment is required before the injection of nZVI.
A review of the recent nZVI ield projects reveals large variations in key parameters
[149]. For most ield trials, it seems that changes in contaminant concentrations are the only
information available to gauge the effectiveness of nZVI performance [149-152]. However,
other factors need to be taken into account, such as the size of treatment zones and the
