Enhancement of Microbial Sulfate Reduction for the Remediation of Hydrocarbon Contaminated Aquifers - A Laboratory and Field Scale Demonstration

Description:

Objective(s) of the Research Project:

The primary goal of this project is to design, implement, and monitor a simple but effective enhanced anaerobic bioremediation technology for treating hydrocarbon contamination in aquifers. The specific goals of this project are to:

1. Evaluate existing data for long-term trends in benzene, toluene, ethylbenzene and xylenes (BTEX) concentrations.
2. Use laboratory experiments coupled with geochemical, hydrological, and contaminant characterizations to design the sulfate injection process and to evaluate the feasibility of this approach.
3. Establish baseline contaminant, geochemical, and microbiological conditions prior to nutrient injection.
4. Monitor the performance of the enhanced anaerobic biodegradation process.
5. Identify the applicability and limitations of enhancing sulfate reduction for stimulating BTEX biodegradation

Progress Summary/Accomplishments:

A survey of groundwater and sediments for geochemical, hydrocarbon biodegradation metabolites, and contaminant concentrations, indicate that conditions are suitable for stimulating benzene biodegradation by the addition of sulfate to the aquifer. Laboratory biodegradation experiments confirmed that the addition of sulfate stimulated benzene biodegradation in samples obtained from most of the sampling locations. Groundwater samples continue to be collected from approximately 35 wells on a routine basis for a variety of geochemical and hydrocarbon analyses. These analyses have established the baseline conditions to which post-sulfate injection data will be compared

A recent experiment was conducted with groundwater collected from four wells at the study site to identify the baseline (prior to sulfate injection) microbiological conditions. The wells will be sampled at a later time to identify whether the injection of sulfate stimulated the activity and or growth of sulfate reducing bacteria and anaerobic benzene biodegrading bacteria. The addition of sulfate stimulated sulfate reduction rates in 3 of four wells indicating that sulfate concentration is an important variable governing sulfate reducing activity (Table 1). Sulfate reduction was not stimulated in groundwater from well SI-12D that contained higher levels of endogenous sulfate (>0.1mM). The addition of sulfate had the greatest effect on sample SI-10S that was collected from a highly contaminated area completely void of dissolved sulfate. Interestingly, groundwater from well SI-10S exhibited decreased numbers of culturable sulfate reducing bacteria and the lowest rate of sulfate reduction. These results attest to the importance sulfate limitation in controlling sulfate reduction rates. The benzene biodegradation rate experiments and anaerobic benzene degrading bacteria enumerations are ongoing.

Additional experiments are being conducted to identify whether factors in addition to sulfate availability control sulfate reduction activity and benzene biodegradation. We will also evaluate the impact of anaerobic sulfide oxidation on benzene biodegradation activity. Column experiments will be used to identify whether iron sulfide precipitation impacts hydraulic conductivity.

Supplemental Keywords: biodegradation, bioremediation, groundwater, BTEX, benzene, anaerobic