Environmental Engineering Reference
In-Depth Information
11.3 Fate/Transport of Nanoscale Porous Materials in Porous Media
Groundwater is a major source of drinking water and can be an environmental
concern from both natural and anthropogenic contamination. Remediation techniques
have been introduced including soil vapor extraction (for volatile organic compounds),
pump-and-treat methods, heat treatment, bioremediation, electro-osmosis, permeable
reactive barrier (PRB), injection of reactive materials (e.g., oxidizers), and the in-situ
placement of chemical reactive barriers (CRB) (Rumer and Ryan, 1995). Among them
the CRB is considered as one of the most cost-effective and innovative techniques for
in-situ groundwater remediation (Gillham and O'Hannesin, 1994). This is because CRB
can be injected as mobile slurry to reach the contaminated zone.
INPs can be used as a CRB material, and therefore, have a potential for
developing novel in-situ groundwater remediation methods. For example, INPs are
about 1 to 3 orders of magnitude more efficient than micro to mm size iron particles for
As treatment (Kanel et al., 2005) and have been shown having higher reactivity for other
contaminants (e.g., TCE, PCE, nitrates) than micron size zerovalent iron particles (Li et
al., 2006). The success on application of these INPs for water treatment using different
model contaminants was reported, including As(III), As(V), Cr(III), TCE, PCE, NO 3- ,
humic acids (Giasuddin et al., 2007a), and U(VI) (Joo et al., 2004; Tratnyek and Johnson,
2006). Despite its excellent reactivity, the natural tendency for INPs to aggregate limits
their transport as well as reactivity in the porous media (He et al., 2007; Kanel and Choi,
2007; Kanel et al., 2007b). For example, iron cannot reach the contaminated plum in the
deep groundwater aquifer (generally > 30 m below the surface). To overcome this
critical limitation, various surface modification and particle stabilization strategies have
been developed using various stabilizers such as surfactant (Tween-20) (Kanel et al.,
2007b), polymer (polyacrylic acid) (Kanel and Choi, 2007) (Bettina Schrick et al.,
2004), carboxymethyl cellulose (CMC) (He et al., 2007), starch (He and Zhao, 2005),
noble metals (Elliott and Zhang, 2001) and oil (Quinn et al., 2005). This surface
modified INP (S-INP) can be mobile and theoretically reach the contaminated area in the
deep groundwater aquifer even though their practical application still needs to be tested.
Only a few studies have reported the transport behavior of S-INPs. Schrick et al.,
(2004) studied poly acrylic acid stabilized INP in a glass burette. Transport of S-INPs
(stabilized on surfactant and polymer) in a 1-D column packed with sand was reported
by (Kanel et al., 2007b). Arsenic removal using S-INPs (in S-INP pretreated 10 cm
sand-packed columns containing ~2 g of S-INPs at a flow rate 1.8 mL/min) showed that
100 % of As(III) was removed from influent solutions containing 0.2, 0.5 and 1.0 mg/L
As(III) for 9, 7 and 4 days, providing 23.3, 20.7 and 10.4 L of arsenic free water,
respectively. In addition, it was found that As(III) in 0.5 mg/L feed solution at a flow
rate of 1.8 mL/min was removed by 100%, for more than 2.5 months, with an S-INP
pretreated 50-cm sand-packed column containing 12 g of S-INPs, providing 194.4 L of
 
 
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