Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02h. Optimizing Remedial Systems

Formatted Title:

Anaerobic Metabolism of DDT in an Ex Situ Bioreactor

Background/Objectives:

A groundwater extraction and treatment (GWET) system and barrier wall are used to control migration of groundwater impacted with DDT, DDD, and DDE (collectively DDx). Groundwater concentrations of DDx have been observed as high as 17,000 µg/L. These pesticides are treated by co-precipitation, filtering, and activated carbon to meet the discharge permit limit of 0.01 µg/L. An anoxic fluidized bed bioreactor (FBR) in the process is used to treat chlorate and perchlorate. Recent observations point towards metabolism of DDx in the FBR, and further experiments were carried out to elucidate this process.

Approach/Activities:

An anoxic environment is maintained in the FBR to select for facultative anaerobes, primarily to carry out the reduction of chlorate and perchlorate to chloride. Observations were made of possible metabolism of DDx in this anoxic environment. To evaluate this hypothesis, a slurry with a high concentration of DDx will be prepared and dosed into aliquots of water from the FBR. Each sample was maintained in the anoxic state for a set time, then an aliquot of bleach was added to halt anaerobic activity. The concentration of DDx over time is plotted to assess the kinetics of DDx reduction in this system.

Results/Lessons Learned:

Examination of the DDx concentration versus time did not show any significant correlation, indicating that any decrease in concentration between the FBR influent and effluent is likely due to sorption on the carbon bed. Given that the DDx concentration on the carbon bed is less than expected from a mass balance, it is feasible that DDx metabolism is occurring at the carbon-bacteria interface. But since this carbon concentration is substantial, relying on ex situ metabolism is not a feasible treatment option for DDx remediation.

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Josh Hyrman

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