Simultaneous Removal of Chromium(VI) and CAHs from Groundwater by In Situ Anaerobic Bioremediation: From Pilot to Full Scale

摘要

We present results of the full-scale remediation of the Tenneco Automotive Europe site in Sint-Truiden, Belgium . The groundwater is contaminated, mainly with chromium(Ⅵ) and CAHs (original pollutant mainly TCE), over a total surface area of 24 ha, of which approximately 5 ha on site and 19 ha off site (residential area). The CAH plume is present mainly at a depth of about 12 m bgl, while the chromium(Ⅵ)-plume is mainly present at about 7 m bgl. The remediation plan combines an active source removal action with anaerobic bioremediation of the groundwater pollution plumes by infiltration of molasses as a substrate (electron donor). About 300 molasses infiltration wells were installed at several lines perpendicular to the groundwater flow direction. The remediation action was successfully started by pilot tests in 2002-2004 and subsequently extended to full-scale from 2004 onwards. The molasses induces microbial reduction of both CAHs (forming ethene as a final dechlorination product) and hexavalent chromium (forming insoluble chromium-Ⅲ). After two years of operation, a significant decrease of chromium(Ⅵ) has been observed, as reflected in average decreased chromium levels in groundwater by one to two orders of magnitude. TCE dechlorination has also progressed to a stadium at which mainly DCE and VC remain and substantial quantities of ethene are being produced in the aquifer. The areas that have been treated for the longest periods show almost complete dechlorination. The large-scale groundwater remediation reported in this paper is an example of a risk-based approach of a complex pollution (heavy metals and organic compounds), combining a source and plume treatment leading to a reduction of estimated remediation costs and time as compared to "classical" pump and treat technology. Moreover, the remediation causes no negative impact on the industrial activities or to the neighboring residential area.