Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Chemical and Materials Engineering

First Advisor

Dr. Dibakar Bhattacharyya

Abstract

The detoxification of chlorinated organics from groundwater, such as trichloroethylene (TCE), tetrachloroethylene (PCE), polychlorinated biphenyl (PCB) and carbon tetrachloride (CTC), is a challenging area. Reductive dechlorination has been investigated using iron and iron-based nanoparticles, such as bare Fe, sulfidized Fe (S-Fe) and palladized Fe (Pd-Fe). However, issues including particle agglomeration, difficulties in recycling and particle leaching have been reported to hinder the application and wide usage of these techniques. The integration of nanoparticles and membranes can address these issues because of the large surface area, stability, and the potential for versatile functionalities. In this study, commercial polyvinylidene difluoride (PVDF) microfiltration membranes were functionalized with poly (acrylic acid) (PAA) or poly (methacrylic acid) (PMAA). The functionalization allows the in-situ generation of iron-based nanoparticles through ion-exchange and reduction processes. These membranes were then tested for the removal of chlorinated organics from synthetic and site groundwater.

Both the PAA and PMAA functionalization showed a responsive behavior in water flux through membranes. The deprotonation of carboxyl groups (-COOH → -COO-) makes PAA or PMAA become hydrophilic when pH > pKa. Membrane permeability was decreased by 5-30 folds when pH increases from 2.3 to 10.5. PAA and PMAA are anionic polymers in the water at neutral and basic pH, which can capture metal cations for the in-situ synthesis of metallic nanoparticles through a reduction reaction. Uniform Pd-Fe particles with a size of 17.1 ± 4.9 nm were quantified throughout the pores of membranes using a developed focused ion beam cross-sectioning method. The reactive particles incorporated membranes presented over 96% degradation of 3,3',4,4',5-pentachlorobiphenyl (PCB-126) in less than 15 s residence time in passing through the membrane domains.

Roles of Pd fractions, particle compositions and water parameters (pH and temperature) in degradation were evaluated using 2-chlorobiphenyl (PCB-1) as a model compound. The H2 evolution (Fe corrosion in water) was quantified with various Pd coverages on the Fe surface. H2 can be activated by catalytic Pd for the hydrodechlorination reaction. However, insufficient H2 production was observed under the higher Pd coverage (>10.4%, corresponding to 5.5 wt%), resulting in the hindrance of dechlorination. Pd fractions from 0.5 wt% to 5.5 wt% (1.0% to 10.4% Pd coverage) yielded higher dechlorination performance. In addition, Pd-Fe bimetallic nanoparticles showed an18-fold mass normalized reaction rate (kmass) than that of isolated Pd and Fe nanoparticles.

The investigation of nanoparticles’ intrinsic properties and PCB degradation guided the application of the Pd-Fe nanoparticles incorporated membranes in the treatment of contaminated groundwater. Cooperating with Arcadis Us Inc. (a global environmental consulting firm), the contaminant groundwater was obtained from a hazardous waste site in Louisville, KY. In a single pass of Pd-Fe-PMAA-PVDF membranes (0.5 wt% Pd), chlorinated organics in groundwater sample, such as TCE (177 ppb) and CTC(35 ppb), were degraded to 16 and 0.3 ppb, respectively, at 2.2 seconds of residence time. The surface area normalized reaction rate (ksa) in the treatment of the groundwater followed the order of CTC (0.101 Lm-2min-1)> TCE (0.034 Lm-2min-1)> PCE (0.017 Lm-2min-1)> chloroform (0.002 Lm-2min-1). A long-term study showed less than 5% CTC and 20% PCE remained in a continuous flow through the membranes within the first 5 h (equivalent of 42 L/m2 treatment of water). A significant decrease in degradation performance was found after 36 h continuous flow (equivalent of 299 L/m2 treatment of water), which the reactivity of incorporated nanoparticles was recovered through regeneration using NaBH4. As expected, the on-site technology evaluation also showed effective remediation of the groundwater samples at the similar residence time of the degradation tests in the lab: less than 0.1% CTC, 12% TCE and 18% TCE remained at a residence time of 2.4 seconds. Successful regeneration and reuse of the reactive membranes were also achieved on-site. Analysis of typical samples was also validated by an environmental testing lab (Eurofins TestAmerica, Inc). The on-site remediation evaluation and the studies of regeneration/reuse enhance the optimization of the reactive membrane systems for the potential to scale up.

Alternatives of Pd-Fe were studied in the solution phase to understand the fundamentals. S-Fe were prepared, after the synthesis of precursor Fe0 nanoparticles (spherical, ~35 nm radius), for the long-term study of CTC. Pd-Fe (0.3 mol% Pd) increased the degradation rate by 20-fold (ksa = 0.580 Lm-2min-1) compared to that of Fe while S-Fe presented a greater lifetime (deactivated after 17 days of aging). During the aging process, Fe core was converted to FeOOH and Fe3O4/γ-Fe2O3 which deactivated the particles. The restoration of Fe0 was achieved using NaBH4 (400 mol%), which regenerated Fe and Pd-Fe nanoparticles. Even though the Fe core was also restored for S-Fe, the formed FeSx layers (FeS, FeS2) disappeared. The results suggest that S-Fe extends the longevity of Fe, but the loss of FeSx makes S-Fe eventually perform like Fe in terms of CTC degradation.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.065

Funding Information

This research is supported by the NIEHS-SRP grant P42ES007380 (2014-2020). Partial support is also provided by the NSF KY EPSCoR grant (Grant no: 1355438) (2017-2019).

Available for download on Thursday, March 25, 2021

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