Field assessment of guar gum stabilized microscale zerovalent iron particles for in-situ remediation of 1,1,1-trichloroethane

Abstract

A pilot injection test with guar gum stabilized microscale zerovalent iron (mZVI) particles was performed at test site V (Belgium) where different chlorinated aliphatic hydrocarbons (CAHs) were present as pollutants in the subsurface. One hundred kilograms of 56μm-diameter mZVI (~70gL(-1)) was suspended in 1.5m(3) of guar gum (~7gL(-1)) solution and injected into the test area. In order to deliver the guar gum stabilized mZVI slurry, one direct push bottom-up injection (Geoprobe) was performed with injections at 5 depths between 10.5 and 8.5m bgs. The direct push technique was preferred above others (e.g. injection at low flow rate via screened wells) because of the limited hydraulic conductivity of the aquifer, and to the large size of the mZVI particles. A final heterogeneous distribution of the mZVI in the porous medium was observed explicable by preferential flow paths created during the high pressure injection. The maximum observed delivery distance was 2.5m. A significant decrease in 1,1,1-TCA concentrations was observed in close vicinity of spots where the highest concentration of mZVI was observed. Carbon stable isotope analysis (CSIA) yielded information on the success of the abiotic degradation of 1,1,1-TCA and indicated a heterogeneous spatio-temporal pattern of degradation. Finally, the obtained results show that mZVI slurries stabilized by guar gum can be prepared at pilot scale and directly injected into low permeable aquifers, indicating a significant removal of 1,1,1-TCA.

Pressure-controlled injection of guar gum stabilized microscale zerovalent iron for groundwater remediation

“…Fig. 8 shows that a quite extended reactive zone within a ROI approximately equal to 0.8 m around the injection well was achieved, and the maximum measured distance reached by ZVI particles was 1.7 m. Particle migration was mainly horizontal from the well screen (located from 4.5 to 7 m), and mZVI was not detected above 4.5 m. All these findings suggest that, even if preferential flow paths were created (as evidenced by the pressure logs during delivery of the mZVI slurry), no migration pathways toward the upper layers nor daylighting, which are both typical of fracturing delivery in shallow aquifers, were evidenced (Velimirovic et al, 2014c).…”

“…Even if some successful pilot and full scale applications of both nZVI and mZVI have been recently reported using different injection technologies (Elliott and Zhang, 2003;He et al, 2010;Johnson et al, 2013;O'Carroll et al, 2013;Quinn et al, 2005;Su et al, 2012;Velimirovic et al, 2014c), specific studies on the preferable delivery techniques are, to the authors' knowledge, still lacking, and the topic still needs to be further investigated. As a general rule, a field injection can be performed according to two different regimes: (i) permeation injection, which generates a uniform particle distribution in the subsurface and ensures the contact between particles and contaminants, or (ii) fracturing injection, which consists in injecting fluids and particles at a pressure exceeding the porous medium critical pressure, thus generating a non-uniform distribution if the process is not properly designed and controlled.…”

“…In several field applications a permeation injection is practically unfeasible, due to the constraints mentioned above, and fracturing injection is the only viable approach. As an example, the authors previously reported a field injection in a low permeability contaminated aquifer, where the ratio of particle to aquifer grain size greatly exceeded the threshold limit for straining (Velimirovic et al, 2014c). In that study, the low permeability of the medium, the use of large mZVI particles (in the order of several tens of microns), and consequently the need of a high polymer concentration (7.2 g/l, resulting in a zero shear viscosity close to 10 Pa s), required a high injection pressure, and a direct push delivery system was adopted.…”

Guar gum solutions for improved delivery of iron particles in porous media (Part 2): Iron transport tests and modeling in radial geometry

“…Great efforts have been devoted so far to the identification of the mechanisms controlling the transport of NZVI (namely physical-chemical interactions with the porous medium, magnetic attraction among particles, filtration and straining of aggregates, sedimentation, etc), and several approaches have been proposed to model its transport and retention in porous media (Kanel et al, 2007;O'Carroll et al, 2013;Petosa et al, 2010;Tiraferri and Sethi, 2009;Torkzaban et al, 2012;Tosco and Sethi, 2010;Yan et al, 2013). On the other hand, fewer studies focused on the mobility of microscale iron (Dalla Vecchia et al, 2009b;Tosco and Sethi, 2010;Velimirovic et al, 2014). In this case, the shear thinning properties of the dispersant fluid, along with the colloidal stability or instability of the suspension, play a major role.…”

Integrating NZVI and carbon substrates in a non-pumping reactive wells array for the remediation of a nitrate contaminated aquifer

“…Contrary to previous works described in the literature, which report the use of millimetric ZVI as filling material in the PRBs, in this work nanoscale zero valent iron (NZVI) is proposed for use in combination with the carbon substrates. Compared to millimetric or micrometric iron particles (MZVI), NZVI has a much larger specific surface area, which results not only in a faster degradation of contaminants (Tratnyek and Johnson, 2006;Huang et al, 2013;Tosco et al, 2014;Karn et al, 2009;Comba et al, 2011a;Comba et al, 2011b), but also in an increased corrosion and reduced lifetime, which makes sometimes MZVI preferable for its higher longevity (Velimirovic et al, 2014;Luna et al, 2015;Gastone et al, 2014). Hazards of NZVI handling during the transportation, handling, and injection of the NZVI are higher compared to MZVI (Renn and Rocco, 2006), and the impact of eventual surface modification (e.g., by noble metals) to enhance NZVI reactivity and stability may increase toxicity (Pherat et al, 2009;Hosseini et al, 2011).…”