03/20/2025
By Danielle Fretwell
The Francis College of Engineering, Department of Civil and Environmental Engineering, invites you to attend a Doctoral Dissertation defense by Lingfei Fan on: "Developing Materials and Monitoring Tools for Mitigating Chlorinated Ethenes and Other Persistent Organic Contaminants."
Date: Thursday, April 3, 2025
Time: 2 - 5 p.m.
Location: Southwick Hall 240
Committee:
Advisor: Weile Yan, Associate Professor, Department of Civil and Environmental Engineering, UMass Lowell
Committee Members*
1. Bridgette M. Budhlall, Professor, Department of Plastics Engineering, UMass Lowell
2. Clifford Bruell, Professor, Department of Civil and Environmental Engineering, UMass Lowell
3. Xiaoqi Zhang, Professor, Department of Civil and Environmental Engineering, UMass Lowell
Abstract
Chlorinated solvents are among the most frequently detected contaminants in the underground environment due to their historical use in industrial applications and their resistance to natural degradation. At contaminated sites, it is difficult to quantify the efficacy of abiotic dechlorination in the field due to the co-occurrence of microbial dechlorination and other processes that lead to contaminant attenuation. In recent years, various forms of zerovalent iron (ZVI) materials have been used to degrade chlorinated solvents. As most lab studies focus on the reactions of TCE, the performance of ZVI on other commonly detected chlorinated ethenes, including intermediate products of TCE degradation, is less well characterized. In this study, the author investigated the degradation rates of perchloroethene (PCE), dichloroethene isomers (DCEs), and vinyl chloride (VC) using sulfur-amended nanoscale-ZVI (S-nZVI) and sulfur-amended bulk ZVI (S-ZVI). Furthermore, the experimental results indicate that the improvements of sulfur treatment in dechlorination rates follow the order of TCE > trans-DCE > PCE ~ cis-DCE ~ 1,1-DCE, suggesting the enhancement effect varies with different chlorinated contaminants. Increasing the sulfur dosage (i.e., the S/Fe mole ratio increasing from 0.0013 to 0.5) has a strong effect on the reaction rates. For all chloroethenes except for PCE, the greatest kinetic improvement effects were observed at the lowest sulfur dose (S/Fe ratio = 0.0013), and moderate improvements were achieved at the highest sulfur loading (S/Fe ratio = 0.5). Compared to the beneficial effects of sulfidation on nZVI, sulfur treatment of a commercially sourced ZVI product (Peerless ZVI) hinders the degradation rate of VC, exhibiting a rate at least six times slower than that of unmodified ZVI, which were attributed to the presence of low levels of metal impurities in Peerless ZVI. To assess the abiotic dechlorination rates at remediation sites, an in situ reactive sampler capable of capturing acetylene, a unique product of abiotic dechlorination of PCE and TCE, was developed. The reactive sampler is based on copper-catalyzed cycloaddition between terminal alkyne and azide groups, also known as CuAAC click chemistry. This reaction is highly specific and it produces a stable triazole product at a quantitative yield, thereby permitting a sampling scheme to capture acetylene arising in the underground environment for quantitation. Laboratory microcosm results demonstrate that this azide-based acetylene sampling tool can provide sensitive and quantitative measurement of acetylene formed during TCE dechlorination, with potential applications in groundwater monitoring and remediation. In the last part of this dissertation research, effort was extended to another class of persistent organic contaminants, plastic additives, to develop optimized methods for extracting, purifying, identifying, and quantifying plastic additives including antioxidants and UV stabilizers. The effectiveness of high-performance liquid chromatography (HPLC) fractionation combined with pyrolysis gas chromatography-mass spectrometry (Py-GCMS) or gas chromatography-mass spectrometry (GCMS) for precise identification and quantification of antioxidants and UV stabilizers were demonstrated using commercial masterbatch and laboratory compounded plastic resins. These methods provide valuable means to examine the environmental implications of plastic contamination in future studies.