Development of Alkoxysilanes as Slow Release Substrates for the Anaerobic/Aerobic Transformation of Chlorinated
Solvents
Lewis Semprini
Oregon State University
E-mail: Lewis.Semprini@orst.edu
Goal
The goal of this research is to investigate the use of silicon based organic compounds as slow release substrates to promote both the
anaerobic and aerobic transformation of chlorinated aliphatic hydrocarbons (CAHs). The silicon based organic compounds (tetraalkoxysilanes)
slowly hydrolyze to generate organic compounds that undergo fermentation reactions to drive anaerobic transformations of CAHs. Recently
we have found that these same compounds can serve as cometabolic substrates to drive the aerobic oxidation of trichloroethene (TCE) and
1,2-cis-dichloroethene (cis-DCE). Thus there is potential for sequential anaerobic/aerobic treatment. The objectives of the laboratory studies
are to determine how passive biological reactive barriers can be created by the injection of these compounds into the subsurface. The specific
objectives are: 1) to study the physical transport of tetralkoxysilanes in porous media and to determine their abiotic hydrolysis rates; 2) to
conduct anaerobic transformation studies in continuous flow columns; 3) to conduct anaerobic/aerobic transformation studies in continuous
flow columns having an anaerobic zone followed by an aerobic zone.
Rationale
Effective methods for the bioremediation of subsurface CAH contamination requires passive, simple, and low cost treatment
systems. The proposed research will investigate novel system(s) for driving these enhanced microbial reactions. Silicon based organic
compounds will serve as slow release substrates to drive both anaerobic and aerobic transformations. Passive biological barrier systems might
therefore be created through the injection of silicon based organic compounds into the subsurface. This research will focus on transport,
chemical, and biological processes of importance for the development this passive treatment system.
Approach
Transport and hydrolysis studies will be performed in two laboratory systems: 1) small laboratory columns operated in a batch
exchange mode and 2) larger laboratory columns operated in a continuous flow mode. The studies will evaluate the rate of hydrolysis
dependence on 1) the tetraalkoxysilanes structure; 2) the loading of the compound on the aquifer materials upon filtration, and 3) the flowrate
through the system. Biological transformation studies will then be performed with columns used for transport and hydrolysis studies. The
biostimulation of the anaerobic community and transformation of the CAHs will be evaluated in a well-controlled 1-D flow geometry that
simulates a passive barrier. The columns will also be bioaugmented with an effective culture that completely transforms TCE to ethene. We
will then progress to sequential aerobic/anaerobic column studies.
Status
Currently we are determining on which contaminated sites we will focus our laboratory studies. The potential of tetrabutoxysilane
(TBOS) to drive the anaerobic transformation of TCE is being evaluated in microcosm studies for three sites: 1) Site-300, Lawrence Livermore
National Laboratory (LLNL), where TBOS drives the transformation of TCE to c-DCE; 2) the Pt. Mugu Naval Weapons Station, CA, where
TBOS transforms TCE to vinyl chloride and ethene, with the last step of VC to ethene being very slow; and 3) the Evanite Site in Corvallis,
OR, where TCE is being rapidly transformed to ethene. Thus, TBOS has been demonstrated to promote TCE transformation to varying
extents, which are site specific.
Copyright © Georgia Tech Research Corporation, 2000.
All Rights
Reserved.
Make comments to: mark.hodges@gtri.gatech.edu
Last modified on: March 16, 2000.
URL: http://www.hsrc.org/