Foam as a Vehicle for Nanoparticle Delivery in Unsaturated Porous Media
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Date
2019-05-23
Authors
Sadeghi Ardestani, Zahra
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Accidental releases, spills, and leaks of petroleum hydrocarbons (PHCs), such as gasoline and jet fuel, can result in subsurface contamination. PHCs that become entrapped as a residual light non-aqueous phase liquid (LNAPL) in the unsaturated zone often serve as a long-term source to groundwater contamination depending on the composition. Technologies used to remediate these residuals are categorized according to where the treatment occurs (in situ vs ex situ). In situ treatment technologies are preferred by the remediation community since they are typically more economical, efficient, and environmentally friendly. Nanoremediation is an emerging in situ treatment technology that has received attention since it has the potential to reduce both the cost and the time to clean-up contaminated sites. Nanoremediation obtains its advantage from the use of nanoparticles that have higher reactivity owing to their increased surface area. Appropriate delivery of engineered nanoparticles (ENPs) into the contaminated sites is crucial for effective treatment. Liquid-based delivery of ENPs to the unsaturated zone is a challenge due to the limited lateral transport and restricted contact between ENPs and contaminants. Foam is potentially capable of overcoming some of the challenges associated with liquid-based delivery of ENPs. This thesis focuses on the investigation of foam capability as a vehicle to deliver Pluronic coated iron oxide core nanoparticles in unsaturated porous media. A multi-criteria decision analysis (MCDA) was used to select foaming agents (surfactants) which were then screened to determine foam properties, and used in a column transport study to investigate the capability of foam to transport ENPs in unsaturated media. Based on the MCDA results, five surfactants (Steol CS-460, Bioterge AS-40, SDS, Ammonyx LO, and Rhamnolipids) were selected. These surfactants were added to Milli-Q water or synthetic groundwater to prepare foaming solutions, and the foamability and foam stability of the generated foams were determined. Steol CS-460 and Bioterge AS-40 were shown to have the highest foamability and foam stability and therefore, were selected for the subsequent experimental efforts. Ammonyx LO was also used for comparison purposes. The three surfactants enhanced the foamabilitiy of the ENPs. Steol CS-460 and Bioterge AS-40 increased the foam stability of the ENPs, whereas Ammonyx LO did not noticeably change it. Foams generated by Steol CS-460, Bioterge AS-40, or Ammonyx LO were able to support the ENPs. It was demonstrated that for foam generation, the ENPs were compatible with the foamability of the surfactants and the foam stability of Bioterge AS-40, and Ammonyx LO. However, the stability of the foam generated by Steol CS-460 slightly decreased from 99.2% ± 0.9% to 90.5% ± 0.7% in the presence of the ENPs. The column experiments were designed and conducted to evaluate the capability of foam generated by Steol CS-460, Bioterge AS-40, and Ammonyx LO to transport the ENPs in unsaturated media. The impact of surfactant type and concentration, and initial volumetric water content of the unsaturated porous medium on the capability of foam to transport the ENPs were investigated. The surfactant type was found to affect the capability of foam to transport the ENPs as the ENP mass recovery by the Steol CS-460 foam (101%) and Bioterge AS-40 foam (93%) were significantly higher than the ENP mass recovery by the Ammonyx LO foam (54%), and the ratio of foam outflow rate to the average foam inflow rate was the lowest for Ammonyx LO. The ENP mass recovery remained essentially unchanged as the Steol CS-460 concentration decreased from 0.3 to 0.1 wt%. Furthermore, as the initial volumetric water content of the porous medium decreased from 0.2 to dry condition, the ENP and tracer mass recoveries by the Steol CS-460 foam slightly decreased. Overall, the results of the column experiments indicate that the foam generated by Steol CS-460 was successfully capable to deliver Pluronic coated iron oxide core nanoparticles in unsaturated porous media, and thus foam has the potential to deliver the ENPs in situ.
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Keywords
foam, nanoparticle delivery, surfactant