Topic Area: 8a. Advances in Tools and Techniques for Assessing MNA

Formatted Title:

Methanotrophic Biodegradation and Natural Attenuation of Chlorinated Solvents under Acidic Conditions

Background/Objectives:

Acidic groundwater is common throughout the eastern and southeastern US, including the Northern Atlantic Coastal Plain aquifer system, which runs south from Long Island, New York, through much of North Carolina. Anaerobic bioremediation technologies for trichloroethene (TCE) are often ineffective in acidic aquifers (i.e., pH < 5.5) resulting in either limited biodegradation or accumulation of cis-dichloroethene (cis-DCE) as a terminal product. The primary focus of this research was to determine the extent to which methanotrophs (aerobic, methane-oxidizing bacteria) may contribute to the biodegradation and natural attenuation of chlorinated solvents in low pH groundwater. Secondary objectives entailed evaluating the types of acidophilic methanotrophs and enzymes involved in methanotrophic degradation of cVOCs via current molecular approaches and enrichment and study of methanotrophic organisms present in site samples.

Approach/Activities:

Aquifer samples were collected from an acidic aquifer both upgradient and downgradient of an existing mulch barrier wall designed to promote reductive dechlorination of TCE and other chlorinated volatile organic compounds (cVOCs). Microcosms were constructed with solids and groundwater from the site to quantify the natural attenuation of TCE under aerobic conditions and the effect of methane +/- inorganic nutrient addition on the rates and extents of co-metabolic TCE biodegradation. Traditional microcosm studies as well as studies using ¹⁴C-TCE were conducted. Experiments were also performed with site samples to assess the range of cVOCs that were subject to enhanced rates and extents of cometabolic biodegradation in site microcosms amended with methane +/- inorganic nutrients. Stable isotope probing (SIP), next generation sequencing (NGS), and gene analysis were performed with select microcosms to determine the types of acidophilic methanotrophs and enzymes involved in degradation of cVOCs. Finally, batch studies were conducted with methanotrophic enrichment cultures from the site to evaluate relevant methane and TCE degradation kinetics, optimal growth conditions, and abilities to biodegrade a range of different cVOCs.

Jooho Chung

Affiliation

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Methanotrophic Biodegradation and Natural Attenuation of Chlorinated Solvents under Acidic Conditions