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- Environmental Restoration
- Munitions Response
- Resource Conservation and Resiliency
- Weapons Systems and Platforms
Novel Microbially-Driven Fenton Reaction for In Situ Remediation of Groundwater Contaminated With 1,4-Dioxane, Tetrachloroethene (PCE) and Trichloroethene (TCE)
Dr. Thomas DiChristina | Georgia Institute of Technology
Recent concern over 1,4-dioxane contamination in groundwater is driven by several factors, including the extensive use and improper disposal of 1,4-dioxane in industrial processes, the high mobility of 1,4-dioxane in water, the recalcitrance of 1,4-dioxane to degradation in the environment, and the classification of 1,4-dioxane as a probable human carcinogen. Current 1,4-dioxane remediation technologies generally entail ex situ pump-and-treat procedures that are not cost effective and are unable to remove co-contaminants such as tetrachloroethene (PCE) and trichloroethene (TCE). Cost-effective remediation technologies for in situ removal of 1,4-dioxane and co-contaminants PCE and TCE have yet to be fully developed. The objective of this project is to demonstrate that 1,4-dioxane and co-contaminants PCE and TCE are degraded simultaneously via application of a novel microbially-driven Fenton reaction.
The novel microbially-driven Fenton reaction is driven by the O2-and Fe(III)-reducing microorganism Shewanella oneidensis. The researchers previously used S. oneidensis to drive a Fenton reaction-based, HO radical generating system that degraded pentachlorophenol (PCP), a highly toxic chlorinated compound also widely distributed in contaminated groundwater. In the PCP degradation system, S. oneidensis batch cultures were provided with Fe(III) and exposed to alternating aerobic-anaerobic conditions. During the aerobic phase, S. oneidensis reduced O2 to H2O2, while during the anaerobic phase, S. oneidensis reduced Fe(III) to Fe(II). During the aerobic-to-anaerobic transition period, the produced Fe(II) and H2O2 interacted chemically via the Fenton reaction to form Fe(III), OH- ion, and HO radical which, in turn, oxidatively dechlorinated PCP. The PCP degradation system was autocatalytic since continual inputs of Fe(II) and H2O2 were not required to drive PCP degradation. Fe(III) produced by H2O2-catalyzed Fe(II) oxidation was readily re-reduced back to Fe(II) by S. oneidensis in subsequent anaerobic phases. The researchers also employed the S. oneidensis-driven Fenton system to depolymerize lignocellulosic materials that are used as inexpensive starting materials for biofuel production. Based on these initial findings, the researchers hypothesized that the S. oneidensis-driven Fenton system may oxidatively degrade 1,4-dioxane and co-contaminants PCE and TCE. Recent results demonstrate that 1,4-dioxane is degraded in a manner analogous to PCP and the lignocellulosic materials.
This project consists of two phases, the recently completed proof-of-concept (Phase I) and an extended follow-on study (Phase II). The objectives of Phase I were to: (1) design a microbially driven Fenton reaction that autocatalytically generated hydroxyl radicals and degraded 1,4-dioxane, TCE, and PCE singly or in combination as co-contaminants at circumneutral pH without the need for continual addition of H2O2 or ultraviolet irradiation to regenerate Fe(II), (2) optimize the 1,4-dioxane degradation rates by varying the duration and frequency of the aerobic and anaerobic incubation periods, and (3) determine the pathway for 1,4-dioxane degradation by identifying the transient intermediates produced during the microbially driven Fenton reaction for 1,4-dioxane degradation. The Phase I effort was completed in 2014. The objective of Phase II is to develop alternative in situ remediation technologies based on the microbially driven Fenton reaction for degradation of 1,4-dioxane, PCE, and TCE at contaminated DoD sites. The Phase II efforts will be carried out as a 3-year extension of the Phase I proof-of-concept project. In Phase II, the development of ex situ remediation technologies will entail a series of modifications to upscale and optimize the batch reactor configurations developed in Phase I. The development of in situ remediation technologies will entail a series of flow-through column experiments to identify strategies for controlling the microbially driven Fenton reaction in situ and optimizing contaminant degradation processes with DoD contaminated sediments manipulated under simulated field conditions.
During Phase I, the project team successfully designed a microbially driven Fenton reaction that autocatalytically generated hydroxyl radicals and degraded 1,4-dioxane, TCE, and PCE either singly or in combination as co-contaminants. In comparison to conventional (purely abiotic) Fenton reactions, the microbially driven Fenton reaction operates at circumneutral pH and does not require addition of exogenous H2O2 or ultraviolet irradiation to regenerate Fe(II) as Fenton reagents. The 1,4-dioxane degradation process is driven by the Fe(III)-reducing facultative anaerobe S. oneidensis. Batch cultures amended with lactate, Fe(III), and 1,4-dioxane were subsequently exposed to alternating aerobic and anaerobic conditions. During the aerobic period, S. oneidensis produced H2O2 via microbial aerobic respiration, while during the anaerobic period S. oneidensis produced Fe(II) via microbial Fe(III) reduction. During the transition from aerobic-to-anaerobic conditions, H2O2 and Fe(II) interacted chemically via the Fenton reaction to produce hydroxyl radicals that completely degraded 1,4-dioxane at source zone concentrations (10 mM) in 53 hours with optimal aerobic-anaerobic cycling frequencies of 3 hours. Acetate and oxalate were detected as transient intermediates during the microbially driven Fenton degradation of 1,4-dioxane, an indication that conventional and microbially driven Fenton degradation processes follow similar reaction pathways. The microbially driven Fenton reaction also degraded TCE and PCE both singly and in combination with 1,4-dioxane as co-contaminant. The microbially driven Fenton reaction thus provides the foundation for further development of alternative ex situ and in situ remediation technologies to degrade 1,4-dioxane, TCE, PCE, and potentially PFAS. These results were published in the Phase I Final Report.
Results of this study will provide background data for extending the innovative technologies capable of simultaneously degrading 1,4-dioxane and co-contaminants PCE and TCE to field applications where the approach should be equally effective in source zones and in low-concentration plumes. (Anticipated Project Completion - 2020)
Points of Contact
Dr. Thomas DiChristina
Georgia Institute of Technology
SERDP and ESTCP