| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | July 24, 2012 |
| Latest Amendment Date: | May 1, 2014 |
| Award Number: | 1215837 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Thomas Torgersen
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | July 15, 2012 |
| End Date: | June 30, 2016 (Estimated) |
| Total Intended Award Amount: | $344,411.00 |
| Total Awarded Amount to Date: | $350,411.00 |
| Funds Obligated to Date: |
FY 2014 = $6,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
80 GEORGE ST MEDFORD MA US 02155-5519 (617)627-3696 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
20 Professors Row Medford MA US 02155-5807 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
EnvE-Environmental Engineering, Hydrologic Sciences |
| Primary Program Source: |
01001415DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Evaluation of Partitioning Electron Donors for Enhanced Bioremediation of Chlorinated Solvent Source Zones
Natalie L. Cápiro and Kurt D. Pennell (Tufts University; Medford, MA)
Recent studies have demonstrated that microorganisms are capable of biodegradation within close proximity to chlorinated solvent source zones. This biological activity can enhance (accelerate) aqueous dissolution (removal) of chlorinated solvents, and has the potential to provide more effective source zone treatment, thereby reducing potential exposure and remediation costs. However, the performance of bioremediation, and more specifically, biologically-enhanced dissolution, faces two challenges; sustained release of electron donor (food source) and delivery of electron donor to the intended target. To overcome these limitations, a potential alternative are partitioning electron donors (PEDs), organic compounds (e.g., n-butyl acetate) that are relatively water soluble, but also partition into (directly mix with) chlorinated solvents. When a PED is delivered to the subsurface contaminant source zone, it preferentially partitions into the organic separate phase chlorinated solvent, and then slowly dissolves back into the passing groundwater along with the contaminant. This strategy of electron donor delivery is intended to promote the growth of chlorinated solvent degrading bacteria in close proximity to the contaminant source zone, while minimizing consumption of electron donor in microbial processes not associated with chlorinated solvent bioremediation (e.g., methane production). The specific objectives of this research are designed to assess the physical, chemical and biological processes that govern PED delivery, mass transfer, and consumption to support sustained microbial biodegradation in chlorinated solvent source zones. A combination of laboratory-scale experiments and mathematical modeling will be conducted using trichloroethene (TCE) as a representative contaminant. The research program is structured around four tasks that will: (1) evaluate and select PEDs for detailed study based on abiotic and biotic batch reactor studies, (2) quantify PED delivery and release, and rates of bioenhanced dissolution and degradation in columns containing residual TCE in comparison to current electron donor delivery approaches, (3) measure the spatial distribution and temporal evolution of PED delivery/release, TCE dissolution and degradation, and microbial communities in heterogeneous aquifer cells to assess the potential for improved bioremediation under more realistic conditions, and (4) implement mathematical models to obtain mass transfer and utilization rate parameters from experimental data, and predict responses to alternative PED delivery strategies and subsurface aquifer conditions to support potential scale up to field-application.
The U.S. EPA estimates that more than $209 billion dollars (in constant 2004 dollars) will be needed over the next 30 years to mitigate hazards at 235,000 to 355,000 chlorinated solvent contaminated sites, impacting nearly 30% of U.S. drinking water supplies. Additionally, these cost estimates do not include many sites susceptible to vapor intrusion, which is now recognized as a key exposure pathway in urban areas. The knowledge gained from the testing and validation of this novel remediation technique will provide a sustainable approach to reduce chlorinated solvent source zone longevity and remediation costs through an improved understanding of enhanced biological treatment. Integration of experimental studies with mathematical modeling will yield guidelines and rate parameters necessary for practitioners and researchers to assess PED performance for a range of potential remediation scenarios. Furthermore, the project will incorporate educational initiatives into the research and instructional activities of the investigators, with the goal of extending the impact of acquired knowledge beyond the traditional framework of journal publications and conference presentations. This goal will be achieved through the following initiatives: (a) the inclusion of undergraduate students conducting laboratory research, and (b) recruitment of female and underrepresented minority science and engineering undergraduate and graduate students, (c) dissemination of instructional tools to regulatory agencies and impacted communities.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE) are found at approximately 80% of all Superfund sites with groundwater contamination and are the most prevalent compound found at more than 3,000 Department of Defense (DoD) sites in the United States (US) due to their widespread use as degreasers. Recent studies have demonstrated that microorganisms are capable of bioremediation (breakdown of hazardous substances into less toxic or nontoxic substances) within close proximity to chlorinated solvent contaminant source zones. This biological activity can enhance (accelerate) removal of chlorinated solvents, and has the potential to provide more effective source zone treatment, thereby reducing potential exposure and remediation costs. However, the performance of bioremediation faces two challenges; sustained release of electron donor (food source) and delivery of electron donor to the intended contaminant region. To overcome these limitations, a potential alternative are partitioning electron donors (PEDs), organic compounds that are relatively water soluble, but also partition into (directly mix with) chlorinated solvents. When a PED is delivered to the subsurface contaminant source zone, it preferentially partitions into the organic liquid phase (chlorinated solvent), and then slowly dissolves back into the flowing groundwater along with the contaminant. This strategy of electron donor delivery is intended to promote the growth of chlorinated solvent degrading bacteria in close proximity to the contaminant source zone, while minimizing consumption of electron donor in microbial processes not associated with chlorinated solvent bioremediation (e.g., methane production). The objective of this research was to test and validate this novel approach for electron donor delivery to support sustained microbial biodegradation at the contaminant:water interface and promote biologically-enhanced dissolution (accelerated contaminant removal due to microbial degradation) of chlorinated solvents.
Abiotic batch and column experiments were conducted to quantify mass transfer parameters of candidate PEDs, n-hexanol (nHex), n-butyl acetate (nBA), 2-ethyl-1-hexanol (2E1H) and isopropyl propionate (IPP) in the absence of bacteria. Results of the batch studies consistently demonstrated greater partitioning of the PEDs into TCE than PCE, with nBA outperforming the other PEDs in terms of extent of mass transfer. Under flow conditions, the injection of PEDs in one-dimensional columns packed with sand containing a uniform distribution of residual PCE or TCE resulted in persistent PED release at detectable concentrations (above 5 mg/L) for 8-times (nHex) and up to 52-times (nBA) longer than conservative (non-partitioning) tracers.
Biologically-active batch reactors and column studies were performed to assess the ability of the PEDs to be utilized by bacteria capable of transforming carcinogenic PCE or TCE to benign ethene, and promote biologically-enhanced contaminant dissolution. A microbial consortium BDI that contains multiple bacterial species and strains capable of transformation of PCE-to-ethene was utilized for this component of the study. Biotic batch reactor results indicated that both nBA and IPP are utilized by dechlorinating bacteria to detoxify PCE at slightly slower rates than lactate; however, nBA utilization yielded benign ethene 20% faster than lactate, and required less electron donor mass to provide equivalent support (food supply) for the microbial community. Subsequent biologically-active column experiments, designed to evaluate PED utilization in a dynamic system, utilized the nBA as the PED to assess biologically-enhanced dissolution of the contaminant source zone in comparison to lactate, which is a commonly used electron donor in bioremediation applications. Three methods of electron delivery were evaluated: (1) continuous injection of lactate, (2) pulsed injections of the PED, nBA, and (3) pulsed injections of lactate. At the completion of each column study, biologically-enhanced dissolution and transformation of PCE was greatest for the continuous injection of lactate, while the systems treated with a pulsed injection of nBA yielding an enhancement factor that was 17% less and 50% less in the pulsed lactate column system. Overall, these results suggest that PEDs offer a promising approach for sustained electron donor delivery that could reduce the need for, or frequency of, repeated electron donor injections to support microbial bioremediation of chlorinated solvent contaminant source zones.
Results obtained from this research demonstrate the potential utility of PEDs, a low-intensity, sustainable approach designed to reduce source zone longevity and remediation costs by supporting biological treatment. Knowledge gained in this work improved our understanding of biological-enhanced dissolution at the contaminant:water interface, and can be implemented to support in situ treatment of chlorinated solvent source zones. The project supported three female graduate students and four undergraduates; 2 female Hispanic undergraduates also participated, including a Research Experience for Undergraduates (REU, award #1441714) student in summer 2014. Five presentations were given at scientific meetings, including an invited talk given by the PI at the Battelle Conference on Remediation of Chlorinated and Recalcitrant Compounds. A book chapter is in press and three manuscripts are in preparation for submission to peer-reviewed journals.
Last Modified: 05/24/2017
Modified by: Natalie Capiro
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