Theme: 14. Emerging Contaminants

Topic Area: 14a. 1,4-Dioxane Remediation Challenges

Formatted Title:

Enhanced Aerobic Biostimulation and Bioaugmentation of Chlorinated Solvents and 1,4-Dioxane in Groundwater

Background/Objectives:

In situ bioremediation (ISB) systems were engineered to promote microbial enhanced oxidation of 1,4-dioxane (1,4-D), chlorinated volatile organic compounds (cVOCs) including cis-1,2-dichloroethene (cis-1,2-DCE) and vinyl chloride (VC) in groundwater by integrating biostimulation and bioaugmentation. The plume was originally treated with enhanced reductive dechlorination, which resulted in the plume showing elevated concentrations of cis-1,2-DCE, VC and 1,1-dichloroethene, as well as 1,4-D. To biodegrade cis-1,2-DCE, VC and 1,4-D, aerobic biodegradation was promoted via air sparging and bioaugmentation with Pseudonocardia dioxanivorans CB1190 (CB1190) or 1,4-D-Stroy™.

Approach/Activities:

Approach/Activities. A series of injection and monitoring wells were used in areas with elevated cVOCs and 1,4-D to distribute the aerobic bioremediation amendments. The aerobic bioremediation system involved air sparging along with injection of CB 1190 and a nutrient medium (e.g., nitrogen, phosphorus, potassium and calcium) to support growth of bioaugmented microbes. A quarterly groundwater monitoring program was developed to evaluate effectiveness of the treatment system including parameters, such as cVOCs and 1,4-D concentrations, key microbial genes abundances, and geochemical levels.

A second in situ bioaugmentation was performed at the site in 2023 using CB1190 or 1,4-D-Stroy™ provided by Allonnia. Monthly or quarterly sampling of major electron acceptors, oxidation reduction potential (ORP), key microbial genes, 1,4-D and cVOCs was performed to evaluate effectiveness of these two different microbes on their ability to biodegrade 1,4-D and cVOCs.

Results/Lessons Learned:

Results/Lessons Learned: The following quarter after enhanced reductive dechlorination was performed, an increase in total organic carbon (TOC) was observed in the impacted monitoring wells. The increase in TOC corresponded to a significant decline in competing electron acceptors and in PCE and TCE in wells affected by biostimulation and bioaugmentation.

In areas where aerobic biostimulation and bioaugmentation using CB1190 was applied, there was a major increase in dissolved oxygen and nutrients along with a significant increase in the CB1190 microbial population. This led to a significant reduction in cis-1,2-DCE, VC and 1,4-D in the groundwater. This presentation will discuss results of the recent bioaugmentation event, the impact of the injection on distribution of various amendments in the groundwater and compare the efficacy of CB1190 and 1,4-D-Stroy™ in biodegrading chlorinated ethenes and 1,4-D. Additionally, we will delve into the application of advanced molecular tools used to monitor and evaluate effectiveness of the biostimulation and bioaugmentation amendments.

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Bill Buehler