Abstract:
A novel aerobic process has been developed for the passive cometabolic treatment of contaminant mixtures in groundwater. Our studies have focused on Rhodococcus rhodochrous ATCC 21198 that can concurrently oxidize 1,4-dioxane (1,4-D) and diverse mixtures of chlorinated aliphatic hydrocarbons (CAHs). We found that the short chain alkane monoxygenase (SCAM) responsible for the cometabolism of the contaminants is induced after grown on 1-butanol and 2-butanol, permitting the use of Slow Release Compounds (SRCs) that slowly hydrolyze to produce these alcohols. Methods were developed to co-encapsulate the SRCs and ATCC 21198 in gellan-gum hydrogel beads. ATCC 21198 grows within the gellan-gum beads and upon diffusion into the beads the contaminants are transformed. In batch reactors containing the gellan-gum beads successive additions of a mixture of 1,1,1-trichloroethane (1,1,1-TCA_, cis-dichloroethene (cis-DCE), and 1,4-D were transformed for over 300 days, with the rates of cometabolism correlated with the rates of alcohol release, oxygen consumption and CO2 production. Continuous flow tests have been performed with columns packed with the gellan-gum beads. The columns mimic passive treatment that might be achieved using an in-situ permeable reactive barrier (PBR) constructed with the gellan-gum beads. Over 99% removal of a mixture of 1,1,1-TCA, cis-DCE, and 1,4-D, each at influent concentration of 250 µg/L, was achieved with a hydraulic residence time of approximately 12 hours The columns effectively transformed the contaminant mixture for over 600 pore volumes (300 days). The columns performance was negatively affected when cis-DCE was replaced by 1,1-dichloroethene (1,1-DCE), due to 1,1-DCE transformation product toxicity. The column containing the SRC that produced 2-butanol was more negatively impacted by 1,1-DCE due to the lower biomass that developed in the gellan-gum beads. Studies have also been performed in a 3-D physical aquifer model (PAM) using a funnel-and-gate system with the co-encapsulated gellan-gum beads used to create a cometabolic permeable reactive barrier (CPRB). Isobutene, a reactive surrogate for 1,4-dioxane, was injected into the PAM along with 1,2-dichloroethane (1,2-DCA). Hydrogen peroxide was added as a source of dissolved oxygen (DO). Consumption of DO and 1-butanol in the CPRB demonstrated stimulation of ATCC 21198 within the gellan gum beads. Isobutene oxide, a cometabolic transformation product of isobutene, was observed in groundwater samples from CPRB and isobutene concentrations below the detection limit indicated cometabolic activity. Approximately 65% of the 1,2-DCA entering CPRB was transformed. The study demonstrated the metabolic and cometabolic activity of the gellan gum beads for over 300 days after their emplacement in the CPRB.
Short bio:
Dr. Lewis Semprini is a University Distinguished Professor of Environmental Engineering, in the School of Chemical, Biological and Enviornmental Engineering at Oregon State University. He has published 133 articles and has an H Index of 31 (Web of Science) and has been cited 2946 times. His research spans disciplines such as environmental engineering, environmental science, microbiology, microbial processes for water treatment and the bioremediation of groundwater. Dr. Semprini brings a novel, multidisciplinary background and training to chemical and environmental engineering in the development of microbial processes for the treatment of legacy and emerging contaminants in groundwater. Dr. Semprini has been actively engaged in the development of microbial processes for the in-situ treatment of contaminated groundwater for the past 30 years. These include the aerobic cometabolism for the treatment of chlorinated solvents and emerging contaminants, such as 1,4-dioxane, and the anaerobic treatment of chlorinated solvents using the process of organohalide-respiration. He works at many different scales from tests with pure cultures of bacteria to study microbial kinetics, models microbial processes, laboratory participates in conducting field scale demonstrations of bioremediation. He has performed numerous batch microcosm studies and laboratory column studies with subsurface materials. He has also collaborated on the use of molecular methods to study microbial processes occurring in chemostat reactors, laboratory columns and biofilms. Dr. Semprini served as the Director of the U.S. EPA Western Region Hazardous Substance Research Center as well as the Executive Chair of the OSU Subsurface Biosphere Initiative. He currently serves as the Director of the OSU Clean and Sustainable Water Technology Initiative. Dr. Semprini outreach includes the advising of undergraduate students in research, which includes OSU Honors College Thesis and the publication of peer reviewed journal articles with undergraduate students. Over the past 6 years Dr. Semprini has been studying the encapsulation of pure cultures of bacteria in hydrogels for the cometabolism of mixtures of chlorinated solvents and 1,4-dioxane and for production of methanol using methanotrophic cultures.