Distinguished Professor of Environmental Engineering,
School of Chemical, Biological, & Environmental Engineering
Oregon State University
Dr. Semprini is a Distinguished Professor of Environmental at Oregon State University.
He received his Ph.D. in Civil Engineering from Stanford University in 1986 and was a Research Associate there from 1986 to 1993. As a Stanford Research Associate, he participated in several of the first pilot-scale field demonstrations of in-situ aerobic cometabolism of chlorinated solvents, the anaerobic transformation of carbon tetrachloride, and field scale evaluations of the intrinsic transformation of trichloroethene.
He joined the faculty at Oregon State University in 1993. His research concerns the microbial processes for the remediation of groundwater contamination with a focus on chlorinated solvents. He also performs research on microbial processes for wastewater treatment with a focus on nitrification and biofilm processes. His groundwater remediation research includes both aerobic cometabolism and reductive dehalogenation. His work includes laboratory kinetic analysis, column and chemostat studies that incorporate the use of molecular methods to track microbial populations and their activities, as well as the development of kinetic models. He also has developed methods to probe in-situ microbial activities using push-pull-tests for both aerobic cometabolism and reductive dehalogenation.
His recent work focuses on the biological treatment of complex contaminant mixtures via both aerobic cometabolism and reductive dehalogenation. Studies of aerobic cometabolism involve mixtures of chlorinated solvents and 1,4-dioxane, while studies via reductive dehalogenation involve mixtures of trichloroethene and carbon tetrachloride. He is developing passive methods for aerobic cometabolism by incorporating pure cultures of bacteria with slow release substrates that are encapsulated in hydrogels. He is also working to develop multiple gaseous substrates to cometabically treat complex mixtures of chlorinated solvents and 1,4-dioxane.
Cometabolism of 1,4-Dioxane and Chlorinated Solvent Mixtures by Rhodococcus rhodochrous 21198 Encapsulated in Hydrogels with Slow-Release-Compounds.
Current remediation approaches for contaminants of concern (COCs) including 1,4-dioxane (1,4-D), and chlorinated aliphatic hydrocarbons (CAHs) often rely on expensive ex-situ pump-and-treat methods rather than more preferable in-situ treatment methods. In-situ remediation is also often further complicated by COCs in low permeability zones that act as long-term sources of contamination. Aerobic cometabolic processes may be a reliable and cost effective means for in-situ treatment of mixtures of COCs that are released from zones of low permeability.
We are developing novel aerobic cometabolic treatment processes based on Slow-Release- Compounds (SRCs) to treat COC mixtures. Our studies have focused on a model isobutane-utilizing strain, Rhodococcus rhodochrous ATCC 21198 that can concurrently oxidize 1,4-D and diverse CAHs, including mixtures of 1,2-cis-dichloroethene (cis-DCE), 1,1,1-trichlorothane (1,1,1-TCA) and 1,1-dichloroethene (1,1-DCE) when grown on isobutane as a primary substrate. 1,4-D also induces expression of a short chain alkane monoxygenase (SCAM) responsible for its own biodegradation in strain 21198 growing on alcohols. These observations suggest the broad COC-degrading activity of gaseous alkane-utilizing bacterial strains can potentially be supported using SRCs that produce alcohols. When co-encapsulated with appropriate microorganisms, these SRCs have potential for in-situ treatment of 1,4-D-containing COC mixtures, particularly when they are diffusing from zones of low permeability.
The detection of SCAM expression was evaluated using our rapid and recently developed activity-based labeling (ABL) approach. The ABL approach was combined with activity-based kinetic testing to identify alcohol growth substrates that induce SCAM expression and activity that resulted in cometabolic transformation of 1,4-D and CAHs. Strain 21198 was able to grow on a broad range of primary and secondary alcohols, organic acids, and lactate. Results of ABL measurements showed that highest SCAM activity for strain 21198 was achieved with growth on gaseous alkanes (isobutane, n-butane, propane and ethane). SCAM activity was also observed after growth on 2-butanol, though no induction was observed after growth on 1-propanol, 1-butanol, ethanol, or isobutanol.
The SCAM ABL measurements agreed well with our activity-based kinetic measurements. The rates of cometabolism of 1,4-D, tetrahydrofuran (THF), and propylene were highest when strain 21198 was grown on gaseous substrates. Slower rates of transformation were observed with cells grown on 2-butanol and 2-propanol, while essentially no immediate transformation was observed when the cells were grown on primary alcohols. In resting cell tests, with cells grown on 2-butanol, 1,4-D was immediately transformed suggesting SCAM was synthesized and active during growth on this substrate. In contrast, cells grown on 1-butanol only transformed 1,4-D after a lag period of several hours, indicating the induction of SCAM occurred after, and not during, growth on this alcohol. A series of induction experiments with 21198 cells grown on isopropanol showed induction of SCAM occurred when cells were exposed to 1,4-D and THF. These tests further suggested that some expression of SCAM might be part of a starvation response that occurs when cells are deprived of readily utilizable carbon.
In suspended cell tests, the cometabolism of 1,4-D and 1,1,1 TCA was observed during growth on 2-butanol. The cometabolism of 1,4D and 1,1,1 TCA was correlated with the consumption of 2-butanol, the production of carbon dioxide (CO2), and the increase in optical density (OD). Similar tests conducted with SRCs that produce 1-butanol or 2-butanol with both suspended cells of strain 21198 and with 21198 and the SRC co-encapsulated in gellan-gum. In suspended cell tests, growth of 21198 and cometabolism of 1,4-D and 1,1,1 TCA has been observed with SRCs producing 1-butanol, 2-butanol, and 2-propanol. Strain 21198 was successfully co-encapsulated with the SRCs in gellan-gum beads and high metabolic activity has been maintained in batch tests for over 210 days. Stable hydrogels were also maintained over this period. Results show a mixture of 1,1,1-TCA, cis-DCE and 1,4-D can be cometabolized with SRCs that produce 1-butanol, and 2-butanol. The first-order rates of cometabolism were correlated with the rates of SRC hydrolysis and metabolism, as measured by carbon dioxide consumption and oxygen consumption. The SRC producing1-butanol achieved the highest rates, while the SRC producing 2-butanol produced the slowest rates. The results demonstrate one of the process controls is selecting the appropriate SRC for encapsulation.