Formatted Title
In Situ Bioelectrochemical Remediation of MTBE-Contaminated Groundwater at a Fuel Station in Beijing, China
Background/Objectives
Groundwater contaminated by petroleum hydrocarbons such as BTEX and fuel amendments such as MTBE from leaking underground storage tanks is a widespread issue, particularly at fuel stations. Nonetheless, investigation and remediation of groundwater contamination at decommissioned or operational fuel stations were not a common practice in China until recently.
Petroleum hydrocarbons and MTBE contamination through vadose zone to phreatic groundwater was detected at a fuel station in Beijing in 2019. Remedies including soil vapor extraction, air sparging, and in situ chemical oxidation were implemented for 8 months in 2021. Although substantial mass of contaminants was removed during the process, significant 'rebounds' occurred, with concentrations of MTBE and total petroleum hydrocarbon (TPH) detected up to 41,900 μg/L and 9,920 μg/L, respectively, as reported in January 2023.
E-REDOX-(O) is a patented in situ bioelectrochemical technology that can enhance microbial oxidation of contaminants of concern (COCs) by providing a perpetual conduit for ambient oxygen as the terminal electron acceptor in the otherwise electron acceptors-depleted subsurface matrix, via a unique extracellular respiration process. This technology has minimum site disruption and zero energy consumption. It has been successfully applied to dozens of field projects in North America for BTEX and TPH remediation. The pilot test in Beijing was its first application at a fuel station in China, mainly targeting MTBE.
Approach/Activities
The pilot test was launched in November 2022. The pilot system consisted of two treatment wells and two monitoring wells, located downgradient and side-gradient. E-REDOX-(O) electrodes were installed in the two treatment wells across the respective screen level. Parameters including MTBE, TPH, potential MTBE degradation products (e.g., tert-butanol, formaldehyde, and acetone), relevant geochemical, and electrochemical parameters (e.g., voltage and current) were monitored throughout the 10-month test period. Molecular assays of microbial population, shifts in communities, and functional genes were also conducted.
Results/Lessons Learned
Significant removal of COCs (75.6~97.4% for MTBE and 91.7~95.3% for TPH) was achieved within the pilot test area, along with the detection of tert-butanol, a signature intermediate from aerobic biodegradation of MTBE. Voltage profiles measured in the system demonstrated a corresponding trend with the fluctuation of COCs. Lack of information on potential source onsite and plume migration from upgradient areas, however, complicated the data analyses. Microbial data are being analyzed and to be included in the final presentation. This pilot test for the first time demonstrated the applicability and effectiveness of the E-REDOX-(O) technology for in situ groundwater remediation at fuel stations in China.