Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

O'Carroll, Denis M.

Affiliation

University of New South Wales (UNSW)

2nd Supervisor

Herrera, Jose

Co-Supervisor

Abstract

As far back as the mid-1990s, biogenic sulfidation has been observed during the implementation of iron-based materials for groundwater remediation. This phenomenon has largely been a consequence of natural biogeochemical processes and the prospects of utilizing engineered sulfidated zerovalent iron (ZVI) particles – nano- and/or micro- sized – were not extensively explored. More recently sulfidation of zerovalent iron (ZVI) particles has received considerable attention, highlighting the benefits that engineered/abiotic sulfidation can offer to nZVI, but to date, no field demonstration of the technology has been conducted. The first part of this thesis aims to report the unique challenges and unanswered questions that remain in relation to the emplacement of S-nZVI. nZVI was synthesized on-site using sodium borohydride (NaBH4) and stabilized with carboxymethylcellulose (CMC). Sulfidation was performed in an aqueous-solid fashion with sodium dithionite (Na2S­2O4) as the sulfidating agent. The slurry was gravity fed into a non-native sandy material by a designated injection well. Multiple monitoring wells were installed upstream and downstream of the injection well to monitor particle breakthrough and changes in the aquifer system. In terms of performance, the study suggests the on-site synthesized S-nZVI is mobile in the subsurface. Transport of S-nZVI to the monitoring wells, both downgradient and upgradient, resulted in a significant shift in aqueous phase concentrations of chlorinated volatile organic compounds (cVOCs). Compound specific isotope analysis (CSIA), changes in concentrations of intermediate degradation products, and the increase of ethene concentrations confirmed cVOC dechlorination.

The field demonstration was followed by a bench – scale study on the aging characteristics and reactivity of S-nZVI. Particles were aged in dithionite immediately after synthesis (i.e., without washing). Aged S-nZVI remained reactive towards trichloroethene (TCE) after a 21-day aging period. Results from the aging study suggest particles synthesized on-site under these conditions could remain operational after extended storage.

As knowledge of this growing area increases, this work presents foundational material on field-application of S-nZVI. Results from this field demonstration show sulfidation is a suitable amendment for the development of more efficient nZVI-based treatments for in-situ remediation.

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