Tetraalkoxysilanes as slow-release substrates to promote aerobic and anaerobic dehalogenation reactions in the subsurface

The role of tetrabutoxysilane (TBOS) and tetrakis (2-ethylbutoxy) silane (TKEBS) in promoting the biologically mediated reductive dechlorination of trichloroethylene (TCE) was studied. In groundwater microcosm tests, the transformation products of these alkoxysilanes, present in the groundwater used to construct the microcosms, promoted the microbial reductive dechlorination of TCE. TBOS and TKEBS present in the Lawrence Livermore National Laboratory, CA, (LLNL) Site 300 groundwater slowly hydrolyzed to 1-butanol and 2-ethoxybutanol, respectively, and silicic acid. In microcosm tests, the reduction of TCE to cis-dichloroethylene (c-DCE) was associated with hydrogen consumption as demonstrated by the repeated addition of depleted TCE. Once transformation of TCE to c-DCE was completed, hydrogen accumulated in the microcosms as a result of the slow fermentation of 2-ethylbutanol, and 2-ethylbutyric acid. The above alcohols and organic acids were also present in the filed at LLNL during periods of active anaerobic transformation of TCE to c-DCE. Groundwater monitoring data from LLNL Site 300 indicated that c-DCE is transformed in situ.