Laboratory, field, and modeling studies of bioaugmentation of butane-utilizing microorganisms for the in situ cometabolic treatment of 1,1-dichloroethene, 1,1-dichloroethane, and 1,1,1-trichloroethane

Abstract

A series of laboratory, field, and modeling studies were performed evaluating the potential for in situ aerobic cometabolism of chlorinated aliphatic hydrocarbon (CAH) mixtures, including 1,1,1-trichloroethane (1,1,1-TCA), 1,1-dichloroethane (1,1-DCA) and 1,1-dichloroethene (1,1-DCE) by bioaugmented microorganisms that grew on butane. A butane-grown bioaugmentation culture, primarily comprised of a Rhodococcus sp., was developed that effectively transformed mixtures of the three CAHs, under subsurface nutrient conditions. Microcosm experiments and modeling studies showed rapid transformation of 1,1-DCE with high transformation product toxicity and weak inhibition by butane, while 1,1,1-TCA was much more slowly transformed and strongly inhibited by butane. Field studies were conducted in the saturated zone at the Moffett Field In-Situ Test Facility in California. In the bioaugmented test leg, 1,1-DCE was most effectively transformed, followed by 1,1-DCA, and 1,1,1-TCA, consistent with the results from the laboratory studies. A 1-D reactive/transport code simulated the field responses during the early stages of testing (first 20 days), with the following extents of removal achieved at the first monitoring well; 1,1-DCE (∼97%), 1,1-DCA (∼77%), and 1,1,1-TCA (∼36%), with little or no CAH transformation observed beyond the first monitoring well. As time proceeded, decreased performance was observed. The modeling analysis indicated that this loss of performance may have been associated with 1,1-DCE transformation toxicity combined with the limited addition of butane as a growth substrate with longer pulse cycles. When shorter pulse cycles were reinitiated after 40 days of operation, 1,1-DCE transformation was restored and the following transformation extents were achieved; 1,1-DCE (∼94%), 1,1-DCA (∼8%), and 1,1,1-TCA (∼0%), with some CAH transformation occurring past the first monitoring well. Modeling analysis of this period indicated that the bioaugmented culture was likely not the dominant butane-utilizing microorganism present. This was consistent with observations in the indigenous leg during this period that showed effective butane utilization and the following extents of transformation: 1,1-DCE (∼86 %), 1,1-DCA (∼5%), and 1,1,1-TCA (∼0%). The combination of lab and field scale studies and supporting modeling provide a means of evaluating the performance of bioaugmentation and the cometabolic treatment of CAH mixtures.