1,4-Dioxane is a chemical of emerging concern in groundwater. The project team hypothesized that the inhibitory effects of co-occurring chemicals on microbes might be responsible for limited in situ 1,4-dioxane biodegradation in impacted environments. Additionally, while biodegradation by planktonic cultures is well established, the biodegradation capabilities of biofilms, a preferred growth mode in much of the natural and built environment, are poorly understood. This research project evaluated the suspected limiting effects of co-occurring chemicals and their remedial technologies on 1,4-dioxane biodegradation through the following technical objectives:

• Characterize the effects of the chlorinated solvents trichloroethene and 1,1,1- trichloroethane and their degradation products on 1,4-dioxane biodegradation.
• Determine the effects of metals on 1,4-dioxane biodegradation in bacterial pure cultures.
• Examine the ability of 1,4-dioxane to be absorbed by abiotic adsorbents and be biodegraded by bioaugmented adsorbents.
• Evaluate co-occurring chemical effects on biodegradation of 1,4-dioxane by bacterial biofilms.
• Assess the effects of enhanced reductive dechlorination (ERD) on 1,4-dioxane biodegradation in columns constructed with media from an impacted site, with and without select co-occurring chemicals.
• Analyze microbial composition and dynamic changes during the chemical oxidation and biological processes.

1,4-Dioxane biodegradation was investigated in the presence of chlorinated solvents or metals, which are known to co-exist with 1,4-dioxane at many impacted sites. Differences in degradation kinetics (rates and affinity constants) provided insights into potentially synergistic or competitive interactions between chlorinated solvents, metal ions, and 1,4-dioxane. The biodegradation potential of metabolic and cometabolic 1,4-dioxane-degrading biofilms in batch and column reactors was examined and compared with planktonic cultures. Subsequently, 1,4-dioxane biodegradation by biofilms was evaluated under a variety of flow regimes for various co-occurring chemical mixtures. Column studies were expanded to evaluate the impact of co-occurring chemicals and ERD treatment on 1,4-dioxane biodegradation in environmental samples. Changes in gene abundance and expression indicated mechanisms of toxicity, inhibition, or regulation associated with exposure to the co-occurring chemicals. In addition, microbial community analysis was conducted to examine composition and dynamics changes during a treatment train consisting of chemical oxidation by hydrogen peroxide followed by biological treatment.

Rates of 1,4-dioxane metabolism by Pseudonocardia dioxanivorans CB1190 and cometabolism by propanotroph Mycobacterium austroafricanum JOB5 were sensitive to chlorinated solvent (with vinyl chloride [VC] being the greatest inhibitor) and trace metal (with Cu(II) being the greatest inhibitor) as a co-occurring chemical. While chlorinated solvents negatively impacted 1,4-dioxane biodegradation, CB1190 was found to be capable of biodegrading both VC and cis-1,2-Dichloroethene concurrently with 1,4-dioxane. Biofilms were able to resist chlorinated solvent and metal inhibition to greater extents than planktonic cultures. Granular activated carbon and zeolite were both found to be capable of adsorbing 1,4-dioxane, and, when used as a growth support for biofilms, helped mitigate chlorinated solvent inhibition. Lastly, chemical oxidative/reductive remedial technologies commonly applied to chlorinated solvent plumes were found to have minor effects on subsequent 1,4-dioxane biodegradation due to the resilience of the microbial community.

The results of this project determined the effects of typical co-occurring chemicals and their common treatment technologies on 1,4-dioxane bioremediation. The identification of pure or mixed cultures as well as biogeochemical conditions, which generate desirable enzyme activities in multiple organic-impacted, metal-stressed environments, will guide the design and optimization of bioaugmentation and biostimulation efforts thereby developing the optimum long-term remedial strategies for 1,4-dioxane. These results will also provide fundamental understanding as well as quantitative tools for natural and enhanced bioremediation of 1,4- dioxane-impacted soil and groundwater. Application of the results of this research will ultimately bolster operational capabilities and warfighter preparedness by mitigating the impacts of these chemicals. (Project Completion - 2023)

Gedalanga, P.B., A. Madison, Y. Miao, T. Richards, R. Illes, J. Hatton, W.H. Diguiseppi, J. Wilson, and S. Mahendra. 2016. A Multiple Lines of Evidence Framework to Evaluate Intrinsic Biodegradation of 1,4-Dioxane. Remediation, 27(1):93-114.

Johnson, N. W., P. B. Gedalanga, L. Zhao, B. Gu, S. Mahendra. 2020. Cometabolic Biotransformation of 1,4-Dioxane in Mixtures with Hexavalent Chromium Using Attached and Planktonic Bacteria. Science of the Total Environment, 706:135734.

Liu, Y., N. W. Johnson, C. Liu, R. Chen, M. Zhong, Y. Dong, and S. Mahendra. 2019. Mechanisms of 1,4-Dioxane Biodegradation and Adsorption by Bio-zeolite in the Presence of Chlorinated Solvents: Experimental and Molecular Dynamics Simulation Studies. Environmental Science & Technology, 53(24):14538-14547. 

Miao, Y., N.W. Johnson, P.B. Gedalanga, D.T. Adamson, C.J. Newell, and S. Mahendra. 2019. Response and Recovery of Microbial Communities Subjected to Oxidative and Biological Treatments of 1,4-Dioxane and Co-contaminants. Water Research, 149(2):74-85.

Miao, Y., N. W. Johnson, T. Phan, K. N. Heck, P. B. Gedalanga, X. Zheng, D. T. Adamson, C. J. Newell, M. S. Wong, and S. Mahendra. 2020. Monitoring, Assessment, and Prediction of Microbial Shifts in Coupled Catalysis and Biodegradation of 1,4-Dioxane and Co-contaminants. Water Research, 173:115540.

Myers, M., N.W. Johnson, E. Zerecero-Marin, P. Pornwongthong, Y. Liu, P.B. Gedalanga, and S. Mahendra. 2018. Abiotic and Bioaugmented Granular Activated Carbon for the Treatment of 1,4-Dioxane-Contaminated Water. Environmental Pollution, 240(9):916-924. 

Pornwongthong, P., A. Mulchandani, P.B. Gedalanga, and S. Mahendra. 2014. Transition Metals and Organic Ligands Influence Biodegradation of 1,4-Dioxane. Applied Biochemistry and Biotechnology, 173(1):291-306.

Zhang, S., P.B. Gedalanga, and S. Mahendra. 2016. Biodegradation Kinetics of 1, 4-Dioxane in Chlorinated Solvent Mixtures. Environmental Science & Technology, 50(17):9599-9607.

Zhang, S., P.B. Gedalanga, and S. Mahendra. 2017. Advances in Bioremediation of 1,4-Dioxane-Contaminated Waters. Journal of Environmental Management, 204(2):765-774.

Zhao, L., X. Lu, A. Polasko, N.W. Johnson, Y. Miao, Z. Yang, S. Mahendra, and B. Gu. 2018. Co-contaminant Effects on 1,4-Dioxane Biodegradation in Packed Soil Column Flow-through Systems. Environmental Pollution, 243(A):573-581. 

Theses and Dissertations

Miao, Y. 2019. Microbial Ecology Insights into Natural and Engineered Biodegradation Processes for 1,4-Dioxane (PhD Thesis). University of California-Los Angeles.

Myers, M. 2016. 1,4-Dioxane Biodegradation using Bioaugmented Granular Activated Carbon (Master’s Thesis). University of California-Los Angeles.

Polasko, A.L. 2017. Sequential Anaerobic-Aerobic Biodegradation of Trichloroethylene and 1,4-Dioxane (Master’s Thesis). University of California-Los Angeles.

Pornwongthong, P. 2014. Stable Isotopic and Molecular Biological Tools to Validate Biodegradation of 1,4-Dioxane (PhD Thesis). University of California-Los Angeles.

Zhang, S. 2017. Biodegradation of 1,4-Dioxane in Co-contaminant Mixtures (PhD Thesis). University of California-Los Angeles.