Field Evaluation of the Solvent Extraction Residual Biotreatment Technology

Abstract

The Solvent Extraction Residual Biotreatment (SERB) technology was evaluated at a former dry cleaner site in Jacksonville, FL, where an area of tetrachloroethylene (PCE) contamination was identified. The SERB technology is a treatmenttrain approach for complete site restoration, which combines an active in situ dense nonaqueous-phase liquid (DNAPL) removal technology, cosolvent extraction, with a passive enhanced in situ bioremediation technology, reductive dechlorination. During the in situ cosolvent extraction test, approximately 34 kL of 95% ethanol/5% water (v:v) was flushed through the contaminated zone, which removed approximately 60% of the estimated PCE mass. Approximately 2.72 kL of ethanol was left in the subsurface, which provided electron donorfor enhancement of biological processes in the source zone and downgradient areas. Quarterly groundwater monitoring for over 3 yr showed decreasing concentrations of PCE in the source zone from initial values of 4-350 microM to less than 150 microM during the last sampling event. Initially there was little to no daughter product formation in the source zone, but after 3 yr, measured concentrations were 242 microM for cis-dichloroethylene (cis-DCE), 13 microM for vinyl chloride, and 0.43 microM for ethene. In conjunction with the production of dissolved methane and hydrogen and the removal of sulfate, these measurements indicate that in situ biotransformations were enhanced in areas exposed to the residual ethanol. First-order rate constants calculated from concentration data for individual wells ranged from -0.63 to -2.14 yr(-1) for PCE removal and from 0.88 to 2.39 yr(-1) for cis-DCE formation. First-order rate constants based on the change in total mass estimated from contour plots of the groundwater concentration data were 0.75 yr(-1) for cis-DCE, -0.50 yr(-1) for PCE, and -0.33 yr(-1) for ethanol. Although these attenuation rate constants include additional processes, such as sorption, dispersion, and advection, they provide an indication of the overall system dynamics. Evaluation of the groundwater data from the former dry cleaner site showed that cosolvent flushing systems can be designed and utilized to aid in the enhancement of biodegradation processes at DNAPL sites.

Graphite Electrode as a Sole Electron Donor for Reductive Dechlorination of Tetrachlorethene by Geobacter lovleyi

“…The very low current demands of the microbial process could readily be supplied by solar panels, providing a sustainable bioremediation option. Although G. lovleyi dehalogenates PCE only to cis-DCE, conversion of PCE to cis-DCE near source zones can be very effective for enhanced PCE dissolution, and there can be subsequent treatment of the more soluble compound cis-DCE with more traditional bioremediation strategies (3,4,21). Furthermore, the finding that G. lovleyi directly accepts electrons from graphite electrodes for reductive dechlorination suggests that other organisms capable of complete dechlorination of PCE or dechlorination of other environmental contaminants might be enriched with electrodes serving as the electron donor.…”

Development of Assessment Tools for Evaluation of the Benefits of DNAPL Source Zone Treatment

“…In a staged treatment scenario, the physicochemical remedy removes significant contaminant mass, and, in case of surfactant or co-solvent flushing, delivers electron donors that may stimulate microbial reductive dechlorination activity (Mravik et al 2003;Ramakrishnan et al 2005). Hence, in this sequential approach, reductive dechlorination acts as a "polishing" step that detoxifies residual contaminants, thereby reducing contaminant mass flux and controlling long-term plume development.…”

Microbially enhanced dissolution and reductive dechlorination of PCE by a mixed culture: Model validation and sensitivity analysis

“…In the past two decades, numerous remediation technologies have been developed to treat DNAPL source zones; however, the ability of a single technology to completely remove or destroy all DNAPL mass and reduce dissolved-phase contaminant concentrations below drinking water standards is limited. Among potential in situ remediation technologies, microbial reductive dechlorination has emerged as an attractive DNAPL source zone remedy (Da Silva et al, 2006;Sleep et al, 2006;Schaefer et al, 2010), and as a source zone polishing step to control residual contaminant concentrations following aggressive physicochemical treatment (Mravik et al, 2003;Ramsburg et al, 2004;Christ et al, 2005). During source zone bioremediation, microbial activity lowers dissolved-phase contaminant concentrations, thereby increasing the driving force for contaminant dissolution from the DNAPL to the aqueous phase, a process commonly referred to as bioenhanced dissolution (Yang and McCarty, 2000;Cope and Hughes, 2001;Yang and McCarty, 2002;Adamson et al, 2003;Sleep et al, 2006;Glover et al, 2007;4 Amos et al, 2008).…”