Intrinsic remediation of trichloroethene driven by tetraalkoxysilanes as co‐contaminants: Results of microcosm and field studies

Abstract

Biological reduction of trichloroethene (TCE), driven by the transformation products of tetraalkoxysilanes, was investigated in seasonal field monitorings and anaerobic groundwater microcosms. Under anaerobic conditions, tetraalkoxysilanes such as tetrabutoxysilane (TBOS) andtetrakis (2-ethylbutoxy) INTRODUCTIONTrichloroethene (TCE) is a common groundwater contaminant in aquifers throughout the United States (Westrick et al., 1984).TCE ranks in the top ten priority pollutants listed by the U.S. Environmental Protection Agency (EPA) (Federal Register, 1989). Over the past decade, microbial degradation of TCE has been extensively studied (Hopkins et al., 1993;Mars et al., 1996;Alvarez-Cohen & McCarty, 1991;Gibson & Sewell, 1992;Maymo-Gatell et al., 1997;Distefano et al., 1992;Fennell et al., 1997;Smatlak et al., 1996;Ballapragada et al., 1997;Sharma & McCarty, 1996;Semprini et al., 1995). Reductive dechlorination under anaerobic conditions and aerobic cometabolic processes are the predominant pathways for TCE transformation. In aerobic cometabolic processes, fortuitous oxidation of TCE is catalyzed by the enzymes induced and expressed for the initial oxidation of the growth substrates (Hopkins et al., 1993;Mars et al., 1996;Alvarez-Cohen & McCarty, 1991). In the reductive dechlorination process,TCE serves as an electron acceptor and chlorine atoms are replaced by hydrogen (Gibson & Sewell, 1992;Maymo-Gatell et al., 1997;Distefano et al., 1992;Fennell et al., 1997;Smatlak et al., 1996;Ballapragada et al., 1997 (Gibson & Sewell, 1992;Distefano et al., 1992;Fennell et al., 1997;Smatlak et al., 1996;Ballapragada et al., 1997) have been shown to support the dechlorination reaction. A range of dechlorinating cultures have been isolated and studied to determine the extent of dechlorination (Distefano et al., 1992;Holliger et al., 1993;Neumann et al., 1994;Smatlak et al., 1996;Maymo-Gatell et al., 1997;Fennell et al., 1997;Ballapragada et al., 1997;Holliger et al., 1998;Löffer et al., 2000). Incomplete dechlorination to cisdichlorethene (c-DCE) or vinyl chloride (VC) is often observed. However, some cultures are reported to dechlorinate completely to ethene (Distefano et al., 1992;Fennell et al., 1997;Smatlak et al., 1996;Ballapragada et al., 1997).The potential for enhancing anaerobic transformation processes for bioremediation is currently being tested and several recent studies have focussed on the role of H 2 (Fennell et al., 1997;Smatlak et al., 1996;Ballapragada et al., 1997) in the reductive dechlorination process. It has been shown that H 2 , generated from more complex organic substrates via fermentation, can serve as the ultimate electron donor in the dechlorination of TCE (Fennell et al., 1997;Smatlak et al., 1996;Ballapragada et al., 1997). In natural systems, H 2 -utilizing microorganisms include methanogens, acetogens, sulfidogens, and dechlorinators.The dechlorinators must compete with these other hydrogenotrophs for the evolved H 2 (Smatlak et al., 1996;Ballapragada et al., 1997). A significant advantage f...

Bacterial community analysis of shallow groundwater undergoing sequential anaerobic and aerobic chloroethene biotransformation

“…Excess amounts of these two carbon and energy sources promote oxygen depletion and anaerobic conditions, as shown previously (Vancheeswaran et al , 2003). Fermentation of the alcohols then can provide an ample supply of dissolved molecular hydrogen, as demonstrated in microcosms prepared from site materials (Vancheeswaran et al , 2003). Dehalorespiring organisms may use this energy source to perform the reductive dechlorination of TCE to DCE (Lowe et al , 2002; Vancheeswaran et al , 2003).…”

“…Accordingly, the hypothesized multi‐step process of complete chloroethene degradation is initiated by the established mechanism of 2‐ethylbutanol and n ‐butanol release from the hydrolysis of TKEBS (Vancheeswaran et al , 2003). Excess amounts of these two carbon and energy sources promote oxygen depletion and anaerobic conditions, as shown previously (Vancheeswaran et al , 2003). Fermentation of the alcohols then can provide an ample supply of dissolved molecular hydrogen, as demonstrated in microcosms prepared from site materials (Vancheeswaran et al , 2003).…”

“…Potential electron donors for dehalogenases are dihydrogen and fumarate, both common end‐products produced by fermentative mixed microbial communities. At Site 300, fermentation of 2‐ethylbutanol and n ‐butanol, released continuously during slow hydrolysis of silicon lubricants, has been shown to support reductive dechlorination of TCE to cis ‐DCE (Vancheeswaran et al , 2003). The accumulation of cis ‐DCE under anaerobic conditions is problematic; however, it may biodegrade aerobically under favorable conditions (Bradley & Chapelle, 1998; Azizian et al , 2005).…”

Microbial Transformations at Aqueous-Solid Phase Interfaces: A Bioremediation Approach

“…4 Si], contain four oxygen bridges from the central silicon atom to the corresponding organic (alkoxy) groups. These compounds are widely used as heat-exchange fluids, sealants, and lubricants because of their excellent thermal properties [24,[421][422][423]. At Lawrence Livermore National Laboratory site 300, these compounds along with trichloroethylene (TCE) were used in heat-exchanger pipes at their materials testing facility [421][422][423].…”

“…Vancheeswaran et al [421][422][423] investigated the attenuation of silicon-based organic compounds (i.e., tetraalkoxysilanes) along with TCE as subsurface contaminants by abiotic hydrolysis and biological mineralization at Lawrence Livermore National Laboratory site 300. They reported, under abiotic conditions, the hydrolysis of the alkoxysilanes such as TBOS and TKEBS to 1-butanol and 2-ethylbutanol, respectively, and silicic acid.…”