Dissertation
Exploring the limits of aerobic vinyl chloride and cis-dichloroethene biodegradation under suboxic conditions
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2021
DOI: 10.17077/etd.006310
Abstract
Vinyl chloride (VC) and cis-dichloroethene (cis-DCE) are toxic chemicals and common groundwater pollutants, and VC is a known human carcinogen. Chlorinated ethene (CE) contamination, including VC and cis-DCE, is commonly treated through reductive dechlorination by anaerobic bacteria. Aerobic processes are also known to degrade VC and cis-DCE. Aerobic biodegradation of VC and cis-DCE have been well studied under laboratory conditions, but its role under field conditions is still poorly understood. One major gap in the current understanding of aerobic VC and cis-DCE biodegradation is its role under suboxic (<1 mg/L dissolved oxygen) conditions that often prevail near CE source areas. Ethene utilizing bacteria, known as etheneotrophs, are of particular interest for aerobic VC and cis-DCE biodegradation. Etheneotrophs can cometabolize VC and cis-DCE, and in many cases can utilize VC directly. Etheneotrophs are abundant in groundwater at CE contaminated sites, and they have been shown to grow under very low oxygen conditions in the lab. Yet, little is known about their role in CE biodegradation in the field.
An improved understanding of VC and cis-DCE biodegradation under low oxygen conditions could increase the efficiency and sustainability of CE remediation and to expand the use of Monitored Natural Attenuation as a remedial alternative. The overall objective of the studies presented here is to better define the role of aerobic VC and cis-DCE degrading bacteria under suboxic conditions, and to provide practical guidance for expanding the role of aerobic CE biodegradation as a site remediation strategy.
The distribution of etheneotrophs and a geochemical characterization of their habitat was investigated through high-resolution soil sampling of a CE contaminated site. Etheneotrophs were found to be abundant near the CE source areas, and even in seemingly anaerobic environments. Aerobic and anaerobic VC degrading bacteria were found to have overlapping habitats. Microscopic examination of soil samples was used to investigate the role of biofilms and determine if aerobic and anaerobic VC degrading bacteria coexisted on a very fine (micrometer) scale. Etheneotrophs were found to exist in multispecies biofilms. These biofilms are sparse (i.e., there are large spaces between adjacent cells), and there is little direct contact between cells. Microcosm studies were performed to characterize biodegradation of VC and cis-DCE under suboxic conditions. Both VC and cis-DCE were aerobically biodegraded under suboxic, and even apparently anaerobic, conditions if trace oxygen was provided. Molecular biological tools were evaluated, and found to provide mixed results for assessing biodegradation potential; confounding factors were identified. I conclude that etheneotrophs play an important role of the biodegradation of VC and cis-DCE, and provide guidance for remediation professionals to use these processes as part of a site remediation strategy.
Details
- Title: Subtitle
- Exploring the limits of aerobic vinyl chloride and cis-dichloroethene biodegradation under suboxic conditions
- Creators
- Patrick M. Richards
- Contributors
- Timothy E Mattes (Advisor)Michelle Scherer (Committee Member)Jerald Schnoor (Committee Member)Craig Just (Committee Member)Gregory LeFevre (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Autumn 2021
- DOI
- 10.17077/etd.006310
- Publisher
- University of Iowa
- Number of pages
- 172 pages
- Copyright
- Copyright 2021 Patrick M. Richards
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Many people rely on groundwater from wells as their source of drinking water. Vinyl chloride (VC) and cis-dichloroethene (cis-DCE) are toxic chemicals and common groundwater pollutants, and VC is a known human carcinogen. Removing these chemicals from the environment is costly and challenging. VC and cis-DCE can be detoxified by bacteria by different kinds of bacteria, depending on whether oxygen is present or absent. Treatment usually occurs in the absence of oxygen, which is more typical for contaminated groundwater. However, little is known about how these processes occur when only small amounts of oxygen are present.
An improved understanding of VC and cis-DCE biodegradation under low oxygen conditions could decrease the cost and improve the sustainability of environmental cleanup. In order to improve our understanding of degradation under low oxygen conditions, this study used high resolution field sampling, imaging with microscopes, and laboratory and genetic studies.
These studies found that oxygen-using bacteria were concentrated near the sources of contamination, even when the groundwater had little or no oxygen. These bacteria were found to grow in films on contaminated soil near other bacteria that degraded VC only in the absence of oxygen. Both VC and cis-DCE were consumed under very low oxygen conditions. Genetic tools helped to evaluate biodegradation under low oxygen conditions, but improvements are necessary.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984210528302771
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