Nanoscale zerovalent iron (nZVI) particles were injected into a contaminated sandy subsurface area in Sarnia, Ontario. The nZVI was synthesized on site, creating a slurry of 1 g/L nanoparticles using the chemical precipitation method with sodium borohydride (NaBH4) as the reductant in the presence of 0.8% wt. sodium carboxymethylcellulose (CMC) polymer to form a stable suspension. Individual nZVI particles formed during synthesis had a transmission electron microscopy (TEM) quantified particle size of 86.0 nm and dynamic light scattering (DLS) quantified hydrodynamic diameter for the CMC and nZVI of 624.8 nm. The nZVI was delivered to the subsurface via gravity injection. Peak normalized total Fe breakthrough of 71% was observed 1m from the injection well and remained above 50% for the 24 h injection period. Samples collected from a monitoring well 1 m from the injection contained nanoparticles with TEM-measured particle diameter of 80.2 nm and hydrodynamic diameter of 562.9 nm. No morphological changes were discernible between the injected nanoparticles and nanoparticles recovered from the monitoring well. Energy dispersive X-ray spectroscopy (EDS) was used to confirm the elemental composition of the iron nanoparticles sampled from the downstream monitoring well, verifying the successful transport of nZVI particles. This study suggests that CMC stabilized nZVI can be transported at least 1 m to the contaminated source zone at significant Fe(0) concentrations for reaction with target contaminants.

A pilot scale injection of nanoscale zerovalent iron (nZVI) stabilized with carboxymethyl cellulose (CMC) was performed at an active field site contaminated with a range of chlorinated volatile organic compounds (cVOC). The cVOC concentrations and microbial populations were monitored at the site before and after nZVI injection. The remedial injection successfully reduced parent compound concentrations on site. A period of abiotic degradation was followed by a period of enhanced biotic degradation. Results suggest that the nZVI/CMC injection created conditions that stimulated the native populations of organohalide-respiring microorganisms. The abundance of Dehalococcoides spp. immediately following the nZVI/CMC injection increased by 1 order of magnitude throughout the nZVI/CMC affected area relative to preinjection abundance. Distinctly higher cVOC degradation occurred as a result of the nZVI/CMC injection over a 3 week evaluation period when compared to control wells. This suggests that both abiotic and biotic degradation occurred following injection.

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Soil and groundwater are key components in the sustainable management of the subsurface environment. Source contamination is one of its main threats and is commonly addressed using established remediation techniques such as in-situ chemical oxidation (ISCO), in-situ chemical reduction (ISCR; most notably using zero-valent iron [ZVI]), enhanced in-situ bioremediation (EISB), phytoremediation, soil-washing, pump-and-treat, soil vapour extraction (SVE), thermal treatment, and excavation and disposal. Decades of field applications have shown that these techniques can successfully treat or control contaminants in higher permeability subsurface materials such as sands, but achieve only limited success at sites where low permeability soils, such as silts and clays, prevail. Electrokinetics (EK), a soil remediation technique mostly recognized in in-situ treatment of low permeability soils, has, for the last decade, been combined with more conventional techniques and can significantly enhance the performance of several of these remediation technologies, including ISCO, ISCR, EISB and phytoremediation. Herein, we discuss the use of emerging EK techniques in tandem with conventional remediation techniques, to achieve improved remediation performance. Furthermore, we highlight new EK applications that may come to play a role in the sustainable treatment of the contaminated subsurface.

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