Emerging Core Concepts for Assessment and Enhancement of Abiotic Natural Attenuation of Groundwater Contaminants

Dr. Paul Tratnyek | Oregon Health & Science University



It is now widely recognized that abiotic processes play an important role in the natural attenuation (NA) of groundwater contaminants, and this development has created demand for new and improved methods of measurement and/or enhancement of abiotic NA processes. Most research towards this goal has approached the problem from the perspective defined by many years of work on biotic NA. However, the appeal of abiotic NA also stems from the success of chemical reduction technologies such as those involving zero-valent iron and dithionite. These natural and engineered approaches to contaminant degradation share many fundamental aspects, so there are substantial benefits to treating them as a class of technologies, now known as in situ chemical reduction (ISCR). There is further synergy from recognizing the parallels between ISCR and in situ chemical oxidation (ISCO), which is somewhat more advanced in terms of full-scale commercial application.

Building on the ISCO to ISCR analogy, there are three important and fundamental “core” concepts in ISCO that are emerging as key to ISCR, including all aspects of abiotic NA. These core concepts involve (i) practical metrics of remediation performance, (ii) enhancement by activation and/or mediation, and (iii) consideration of natural reductant demand. The objective of this project is to advance all three core concepts, in parallel, with the net result of providing a more complete and coherent foundation for abiotic NA (and all other variations of ISCR).

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Technical Approach

This project will develop all three core concepts through a combination of critical analysis, laboratory scale experimentation, correlation analysis, and modeling. For the first concept, established performance metrics for other/related applications will be evaluated, data will be collected for performance metric validation, and improved performance metrics will be derived using validated normalization protocols. For the second concept, enhancement strategies will be identified from prospects drawn from a wide range of precedents, the most promising will be tested and calibrated in controlled laboratory experiments, and the prospects for up-scaling these enhancement strategies will be evaluated, considering cost, regulations, etc. For the third concept, the role of aquifer reductant demand will be addressed by developing protocols for measuring reductant demand, experimentally validating these protocols with representative aquifer materials, and incorporating reductant demand into models of abiotic NA processes.

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The expected outcomes of this project will advance the theory and practice of abiotic NA in three complementary areas with potentially far-reaching impact. Metrics for performance that are rigorously defined and widely adopted will allow, for the first time, quantitative comparison of abiotic NA outcomes. Enhancement of abiotic NA by control of activation and/or mediation processes will make this approach more effective where it is already applicable and more flexible for application to a wider range of contaminated sites. Reductant demand characterization will become as essential to evaluation of abiotic NR as oxidant demand characterization is currently for proposed applications of ISCO. (Anticipated Project Completion - 2020)

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Cai, S., B. Chen, X. Qiu, J. Li, P. G. Tratnyek, and F. He. 2020. Sulfidation of Zerovalent Iron by Direct Reaction with Elemental Sulfur in Water: Efficiencies, Mechanism, and Dechlorination of Trichloroethylene. Environmental Science & Technology, 51(1):645-654. [DOI: 10.1021/acs.est.0c05397].

Fan, D., Y. Lan, P. G. Tratnyek, R. L. Johnson, J. Filip, D. M. O'Carroll, A. N. Garcia, and A. Agrawal. 2017. Sulfidation of Iron-based Materials: A Review of Processes and Implications for Water Treatment and Remediation. Environmental Science & Technology, 51(22):13070–13085.  https://pubs.acs.org/doi/pdf/10.1021/acs.est.7b04177

Gong, L., X. Qiu, P. G. Tratnyek, L. Chengshuai, and F. He (2021) FeNX(C)-Coated Microscale Zero-Valent Iron for Fast and Stable Trichloroethylene Dechlorination in both Acidic and Basic pH Conditions. Environ. Sci. Technol.  55(8): 5393–5402. [10.1021/acs.est.0c08176]

He, F., L. Gong, D. Fan, P. G. Tratnyek, and G. V. Lowry. 2020. Quantifying the Efficiency and Selectivity of Organohalide Dechlorination by Zerovalent Iron. Environmental Science: Process & Impacts, 22(3):528-542.

Kocur, C. M. D., D. Fan, P. G. Tratnyek, and R. L. Johnson. 2019. Predicting Abiotic Reduction Rates using Cryogenically Collected Soil Cores and Mediated Reduction Potential Measurements. Environmental Science & Technology Letters, 7(1):20-26.

Qin, H., X. Guan, J. Z. Bandstra, R. L. Johnson, and P. G. Tratnyek. 2018. Modeling the Kinetics of Hydrogen Formation by Zerovalent Iron: Effects of Sulfidation on Micro- and Nano-scale Particles. Environmental Science & Technology, 52(23):13887-13896.

Qin, H., X. Guan, and P. G. Tratnyek. 2019. Effects of Sulfidation and Nitrate on the Reduction of N-nitrosodimethylamine (NDMA) by Zerovalent Iron. Environmental Science & Technology, 53(16):9744-9754.

Qin, C., J. Zhang, C. Zhang, Y. He, and P. G. Tratnyek (2021) Abiotic Transformation of Nitrobenzene by Zero Valent Iron under Aerobic Conditions: Relative Contributions of Reduction and Oxidation in the Presence of Ethylene Diamine Tetraacetic Acid. Environ. Sci. Technol.  55(10): 6828-6837. [10.1021/acs.est.1c00653]

Torralba-Sanchez, T. L., E. J. Bylaska, A.J. Salter-Blanc, D. E. Meisenheimer, M. A. Lyon, and P. G. Tratnyek. 2020. Reduction of 1,2,3-Trichloropropane (TCP): Pathways and Mechanisms from Computational Chemistry Calculations. Environmental Science: Processes & Impacts, 22(3):606-616.

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Points of Contact

Principal Investigator

Dr. Paul Tratnyek

Oregon Health & Science University

Phone: 503-346-3431

Fax: 503-346-3417

Program Manager

Environmental Restoration