Active treatment is necessary for the complete degradation of hPAHs (heavy PAHs). Limitations associated with in-situ biotechnologies treatment of hPAHs include the availability of the contaminant in a form conducive to microbial utilization and an efficient delivery of an appropriate electron acceptor to the contaminated zone.
The underlying objective of this research is to evaluate the effects of intermittent mechanical mixing on mass transfer and bioavailability characteristics of hPAHs in contaminated soils in in-situ intermittently mixed slurry systems.
"Real world" contaminated soil collected from a Southern Maryland Wood Treatment Site (referred to as SMWT soil) is used in the experiments. SMWT soil is contaminated with hPAHs and chlorophenols and contains active bacterial populations including PAH degraders.
A reactor constructed using a 500-mL glass kettle covered with a multi-port glass head plate is being used as a prototype for the conceptual in-situ intermittent slurry reactor. A biodegradation study of the SMWT soil is being conducted in the lab scale reactors. In addition to these intermittently mixed reactors, hPAH biodegradation patterns under continuously and completely mixed conditions are being evaluated. An extraction procedure to maximize the removal of hPAHs from the soil samples has been developed. Results show that a soil sample (~1-2 grams) in 40 mL of methylene chloride and sonicated for four hours results in the most effective extraction of hPAHs from the soil samples. All samples are analyzed on a HP 6890 Series Gas Chromatograph (GC) with flame ionization detector (FID).
Experiments have focused to date on assessing the ability of the indigenous microbial population to effect hPAH degradation. Future experiments will involve bioaugmentation of the reactors with Sphingomonas paucimoblis strain EPA 505, a known phenanthrene and fluoranthene degrader and pyrene cometabolizer.