Thermally Enhanced mobilization and reductive Dehalogenation of a VOC Contaminated Site
ABSTRACT: A pilot VOC remediation is executed in a residential area in The Netherlands. The aim of the pilot is to investigate the efficiency of thermally enhanced mobilization and reductive dehalogenation and to reach groundwater target values of 20 μg/L for PCE, 262 for TCE, 10 for cis-DCE and 2.5 for VC in an interconnected volume of 50% of the pilot treatment zone. Where no residual product was present, heating depleted PCE in soil and groundwater and resulted in a pronounced shift towards degradation of cis-DCE. In presence of residual product, PCE was not completely removed and in groundwater total VOC concentrations increased during the heating only phase. Subsequent heating combined with groundwater extraction lowered the groundwater total VOC concentrations.
Lower numbers of Dehalococcoides were found in soil samples with residual product of PCE, probably outcompeted by PCE and TCE degraders. Laboratory tests revealed that temperatures around 14-16ºC are more favorable for complete dehalogenation to ethene, while dehalogenation to cis-DCE is faster at a temperature of 35ºC. So for optimal biological in situ treatment, temperatures should be kept at 35ºC until PCE and TCE are depleted followed by lower temperature treatment for the conversion of cis-DCE to ethene.
Biodegradation proceeded well in the pilot treatment zone, however the groundwater target values were not reached within the 150 days the pilot has been running. Heating should be applied for a longer period in combination with electron donor addition.

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