Bench-scale evaluation of aerosol delivery for biostimulation and bioaugmentation in the vadose zone.

Aerosol delivery was evaluated for distributing biostimulation and bioaugmentation amendments in vadose zones. This technique involves transporting amendments as micron-scale aerosol droplets in injected gas. Microcosm experiments were designed to characterize reductive dechlorination of trichloroethene (TCE) under unsaturated conditions when delivering components as aerosols. Delivering amendments and/or microbes as aqueous aerosols resulted in complete dechlorination of TCE, similar to controls operated under saturated conditions. Reductive dechlorination was achieved with manual injection of a bioaugmentation culture suspended in soybean oil into microcosms. However, aerosol delivery of the culture in soybean oil induced little reductive dechlorination activity. Overall, the results indicate that delivery as aqueous aerosols may be a viable option for delivery of amendments to enhance vadose zone bioremediation at the field-scale.

Evaluation of strategies for anaerobic bioremediation of high concentrations of halomethanes.

Bioremediation is being considered for groundwater at an industrial site contaminated with carbon tetrachloride (CT), trichlorofluoromethane (CFC-11), and chloroform (CF), at concentrations typically considered too high for biological treatment. 1,1-Dichloroethene is also present. The objective of this study was to evaluate in situ anaerobic remediation by biostimulation alone (lactate, emulsified vegetable oil, and corn syrup), biostimulation (corn syrup) supplemented with vitamin B(12) (cyanocobalamin), and bioaugmentation in combination with catalytic levels of B(12). Three cultures were evaluated for enhancing biotransformation of CT, CFC-11 and CF: two were sulfate reducing enrichments (grown on lactate and ethanol, respectively), based on a high concentration of sulfate in the groundwater; the other was a fermentative enrichment grown on corn syrup. A microcosm study with soil and groundwater (neutralized to pH 7) from the site revealed that bioaugmentation is a potentially feasible treatment approach, with complete biotransformation of 8.8mg/L CT, 26mg/L CFC-11, and 500mg/L of CF in approximately 500days. The lactate-grown sulfate reducing culture and the corn syrup-grown fermentative culture were the most effective. Subsequent bioaugmentation with a chloroethene-respiring culture yielded rapid reduction of 1,1-dichloroethene (9.1mg/L) to ethene. Complete transformation of CT, CFC-11 and CF was also observed with corn syrup+B(12), although the time required was twice as long compared to bioaugmentation. In the presence of B(12), biotransformation of [(14)C]CT and [(14)C]CF yielded mainly CO, CO(2), and organic acids. CT was consistently transformed first, followed by CFC-11 and then CF. Corn syrup was only partially effective for halomethane removal without B(12), but was more effective than emulsified vegetable oil or lactate.