Sulfolane, an industrial solvent used to de-acidify natural gas and selectively remove lighter aromatics from petroleum, has a high affinity for water and is found in the aquifers surrounding sites where it has been improperly handled. To date sulfolane degradation in aquifer substrate has only been studied in three contaminated sites: Western Canada; Brisbane, Australia; and Lathrop, California. Recently, a sulfolane plume located in North Pole, Alaska, was identified as being the largest groundwater contaminant plume in the state and spans roughly a 5.5 by 3.2 km area. Due to the size of the contaminant plume, we questioned if there was any potential for sulfolane biodegradation to occur in subarctic aquifer substrate, and if so, what factors limit biodegradation in situ. To address these questions, aerobic and anaerobic microcosm studies were performed at 4 - 8°C using substrate from the contaminated North Pole aquifer.
Sediment/groundwater slurries and groundwater-only microcosms were established under aerobic conditions. Aerobic sediment slurries contained different sulfolane concentrations with and without nutrient addition. Since portions of the plume also contain hydrocarbon contamination, we assessed the effect of hydrocarbon co-contamination on sulfolane degradation. Anaerobic sediment slurries were established under nitrate and sulfate reducing conditions. Sulfolane was found to degrade only in the presence of an aerated microbial community, with no detectable degradation occurring in sterile controls or in anaerobic incubations. The addition of a mineral nutrient solution significantly stimulated biodegradation at high sulfolane concentrations, but had no effect at low sulfolane concentrations. Hydrocarbon co-contamination retarded the rate of sulfolane biodegradation. In microcosms using groundwater as the sole inoculum, the addition of a nutrient solution was crucial to initiate sulfolane biodegradation.
This research suggests that a way to remediate sulfolane in subarctic aquifer substrate is to modify environmental conditions to biostimulate the metabolic capabilities of indigenous microorganisms present in aquifer substrate.