Event Detail

Event Type: 
Applied Mathematics and Computation Seminar
Friday, October 24, 2008 - 05:00
Gilkey 113

Speaker Info

School of Chemical, Biological and Environmental Engineering

The remediation of subsurface contamination with chlorinated ethenes, such as perchloroethene (PCE) and trichloroethene (TCE), using biological processes is currently being applied in practice. Anaerobic processes are increasingly being used because microbes can grow on the chlorinated ethenes as electron acceptors, where highly chlorinated ethenes, such as PCE and TCE, are successively dechlorinated to dichloroethene (DCE), vinyl chloride (VC), and ethene (ETH) as a non-toxic end product. Engineered remediation usually involves the addition of a substrate (like lactate), that can serve as an electron donor, or that ferment to hydrogen (H2) the ultimate electron donor required for the last steps in the transformation pathway. Development of models that can simulate these complex processed are needed to help design efficient remediation systems.
Laboratory and modeling studies have been conducted with microbial cultures that have been isolated from sites contaminated with TCE and PCE. One culture, which we kinetically characterized in great detail, was isolated from the Evanite site in Corvallis. Kinetic characterization involved the determination of Monod parameters including the maximum utilization rates (kmax) and half-substrate coefficients (Ks) values for each step of the transformation process. Models were also developed for substrate inhibition with more highly chlorinated ethenes inhibiting the transformation of less chlorinated ethenes. Model simulations require the solution of a series of non-linear differential equations for substrate utilization and microbial growth. Simulations performed with independently derived kinetic parameters provided good matches to the results laboratory batch tests with unlimited electron donor availability.
Model development is currently being extended for conditions that include substrate fermentation and the competition for the H2 produced between the dehalogenating populations and other populations including homoacetogens and methanogens. The model formulation requires the inclusion of thermodynamic equations (free energy) along with the kinetic equations. The system of equations is being solved using COMSOL®. Kinetic studies are being conducted in chemostat reactors where quasi-steady-state conditions are developed and then perturbed. The responses observed in the chemostats are being simulated with a consistent set of kinetic and thermodynamic parameters. The eventual goal of this work is to incorporate the system of equations into a flow and transport model to simulate the results of porous media columns studies that are being performed.