In-situ technologies for groundwater treatment: the case of arsenic - In-Situ Remediation of Arsenic-Contaminated Sites - page 19

and Batchelor, 2002; McCormick et al ., 2002; Scott et al ., 2005). Magnetite shows reactivity
toward CCl 4 . Particle diameter plays an important role, with nominal 9 nm magnetite suspensions
exhibiting greater reactivity than 80 nm magnetite suspensions (Vikesland et al ., 2007).
1.6.6 Field application of nZVI injection in subsurface
Nanoparticles are typically injected as slurries (nanofluids) directly into the subsurface envi-
ronment to remediate contaminated groundwater plumes or contaminant source zones and may
be suspended in the injected fluid to prevent particle agglomeration and enhance reactivity and
mobility. Toward this direction, a variety of coatings (e.g., polyelectrolytes, surfactants, polymers,
etc.) and supports (e.g., carbon, silica) have been used to stabilize nanofluids by increasing their
resistance to particle aggregation and facilitating their delivery to target pollutants. According to
the filtration theory, the mobility of colloidal particles in soils is governed by particle properties
(e.g., size distribution, shape, electric charge, concentration) and hydraulic and physicochemical
properties of soil and its environment (e.g., matrix chemical composition, surface zeta potential,
temperature, pore structure, pH, ionic strength, groundwater composition, etc.) (Uyusur et al .,
2010). The foregoing parameters are of key importance for the Brownian diffusion of particles,
their sedimentation and interception, and subsequently for the fate of nanoparticles during their
transport through soil pores. Therefore, there is a need to establish nanotechnology synthesis
routes that will control the mobility/reactivity/stability/toxicity of nanoparticles by adapting the
nanofluids composition to the properties of soil, groundwater, and pollutants. No systematic
study has ever been done to specify the most suitable agents that ensure the stabilization of
adsorptive/reactive nanomaterials and their successful delivery to the target pollutants within
contaminated soils and groundwater.
Karn et al . (2009) have compiled a comprehensive overview of some of the sites treated with
nZVI. Most of these sites are located in the USA (Benett et al ., 2010; He et al ., 2009; Quinn et al .,
2005), and details can be viewed at the website of the Project on Emerging Nanotechnologies
(Kuiken, 2010). In Europe, only a small number of pilot studies and a few full-scale remediation
projects have been conducted (e.g., in the Czech Republic, Italy, and Germany). Before carrying
out a full-scale application of nZVI, precise site investigations and pilot tests are needed, including
the site hydrogeology as well as the geochemistry (Karn et al ., 2009). The hydrogeology influences
the leachability of the particles while the geochemistry indicates potential substances that nZVI
could react with other than the target compounds and thus determines the longevity of the reactive
particles. Pilot tests are conducted to provide information on the amount of nZVI needed and
possible unanticipated challenges. Information about the pilot-tests performed in Europe is shown
in Table 1.4 .
In Europe, full-scale demonstration of the in-situ groundwater remediation by injecting nZVI
has been done on three sites (Müller and Nowack, 2012) contaminated by chlorinated solvents
(PCE, TCE, DCE): (i) Bornheim (Rhein-Sieg-Kreis, Germany); (ii) Horice (Czech Republic); (iii)
Pisecna site (Czech Republic). High pollutant remediation efficiencies (80-90%) were confirmed
at a total cost (including treatment and monitoring) of € 300,000-360,000 (Müller and Nowack,
2010; Müller et al ., 2012).
All field applications carried out in Europe targeted groundwater only, while in the USA, about
half of the site remediation targeted groundwater alone. About one fifth treated groundwater and
soil simultaneously and a small number of site remediation treated sands, clayey silts, or soils
(Karn et al ., 2009). In Europe, nZVI was in most cases injected into high permeability aquifers
(more than one third of sites), 25% targeted fractured bedrock and only a few pilot projects
were carried out in low permeability aquifers, unconsolidated sediments, or sandy gravel. For
another 25% of the projects, the structure of the subsurface was not reported. Generally, it is
agreed that remediation with nZVI in dense geological formations is less efficient and that unsat-
urated media are more difficult to treat. However, in these cases, hydraulic conductivity can be
increased by fracturing and unsaturated zones can be flooded before or during the treatment.
The range of possible applications of nZVI is wide as it can not only effectively degrade organic