Page 314 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Nanomaterials for Groundwater Remediation 299

Nanotechnology has the potential to create novel and effective in situ
treatment technologies for groundwater contaminant source zones.
Rapid advances in nanotechnology have led to the creation of novel
nanoparticles with unique and tunable physical and chemical proper-
ties. Their properties can be adjusted to make them highly reactive
with common organic pollutants, and to minimize the formation of
unwanted toxic by-products. Highly reactive nanoparticles such as
nanoscale zerovalent iron (“nanoiron” or NZVI) (Liu et al. 2005a; Liu
et al. 2005b), nanocatalysts (e.g., Au/Pd bimetallic nanoparticles [Nutt et al.
2005]), or nanosized sorbents (Tungittiplakorn et al. 2005; Tungittiplakorn
et al. 2004) have been developed specifically to remediate contamina-
tion by organic and inorganic contaminants. In principle, their small size
(10–500 nm) also provides an opportunity to deliver these remedial
agents to subsurface contaminants in situ, and provides access to con-
tamination trapped in the smallest pores in an aquifer matrix. Highly
mobile nanoparticles are needed that can transport in the subsurface
to where contaminants are located, which increases the potential for off-
site migration and thus the potential for any unwanted ecotoxicity or
human health risks. The high reactivity, and the potential for facile
delivery directly to the contaminant source, suggests that nanoparticles
can accelerate the degradation rate of contaminants in the source zone,
and decrease the time and cost of remediation relative to traditional
treatment technologies that address the plume.
Here, we focus on recent advances in the use of nanoparticles for
in situ remediation of contaminated groundwater. In particular, the
focus is on the use of nanoscale zerovalent iron and bimetallics (e.g.,
0
Fe /Pd) for the rapid in situ degradation of chlorinated organic com-
pounds and reduction of heavy metals in contaminant source zones. In
situ source zone treatment using nanoiron is one of the early adopters
of environmental nanotechnology. There are already many documented
applications of nanoiron ranging from pilot to full-scale, and early data
suggest that nanoiron can be effective and can lower the costs of con-
taminant source zone remediation in groundwater (Gavaskar et al.
2005). Despite this rush to market, there are critical aspects of nanopar-
ticle-based remediation strategies that have not yet been fully
addressed. The delivery of nanomaterials in the subsurface is analogous
to filtration in porous media. Particle slurries injected into the subsur-
face must migrate from the point of injection through the subsurface to
the source of the contamination. Natural geochemical conditions (e.g.,
pH and ionic strength) can destabilize the nanoparticles and allows
aggregation (labeled A in Figure 8.1). Particle aggregates may then be
removed by straining and pore plugging (labeled B in Figure 8.1). These
same conditions will also increase nanoparticle deposition onto media
grains (labeled C in Figure 8.1). High deposition rates onto media grains