Determining the Partitioning of Chlorinated Solvents into Soybean Oil used during Remediation of DNAPL Source Zones
Wilburn, Eric Beyer
2012
- One of the most commonly detected classes of contaminants in the subsurface is chlorinated solvents. Chlorinated solvents undergo limited natural degradation in the subsurface. Enhanced in situ biodegradation is an effective treatment for subsurface environments contaminated by chlorinated solvents. Enhanced biodegradation of chlorinated solvents involves metabolic reductive dechlorination, which ... read moreis a strictly anaerobic, energy-deriving, process that couples the oxidation of an electron donor to the sequential reduction of chlorinated contaminants (tetrachloroethene (PCE) __� trichloroethene (TCE) __� cis-dichloroethene (cis-DCE) __� vinyl chloride (VC) __� ethane). The biological process relies upon the injection of fermentable substrate to produce the reducing equivalents needed by the anaerobic bacteria. / A major unknown related to engineering applications of metabolic reductive dechlorination is the fate and transport of degradation products within the multiphase environment comprising aqueous and organic phases. The addition of emulsified oils (substrate) to the subsurface essentially creates zones of NAPL, albeit vegetable oil NAPL. The main hypothesis of this research is the emulsified oil phase can sequester contaminants and degradation products within the subsurface. Any such sequestration would obscure engineering interpretations related to the accumulation of cis-DCE and VC, which are more toxic and indicative of incomplete dechlorination. Moreover, knowledge of the mass of all degradation products formed during bioremediation is critical when assessing the extent and kinetics of degradation. / This study elucidates the equilibrium partitioning of three chlorinated solvents/degradation products (PCE, TCE and cis-DCE) between a representative vegetable oil (soybean oil) and the aqueous phase. Equilibrium experiments were completed and then analyzed for behavior over environmentally relevant concentrations of these chlorinated solvents. Deviations from ideal solution theory (Raoult_�_s Law Analogy) were identified at low concentration in all systems. Dilute regions for PCE, TCE and cis-DCE extend from zero concentration up to approximately 175 mg/L, 400 mg/L, and 2250 mg/L respectively. Partitioning within these dilute regions was modeled using Henry_�_s Law, with partition coefficients (mole-fraction basis) of (2.20�� 0.155)�_�105, (3.37��0.178)�_�103, and (1.33��0.03)�_�103 (i.e., XCSDP in Organic Phase/XCSDP in Aqueous Phase) at 22 �� 2��C for PCE, TCE, and cis-DCE, respectively. Future efforts should focus on extending these measurements into the more concentrated region which will permit more rigorous modeling of the liquid-liquid equilibrium using excess free energy models. /read less
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- 3x817059t
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- tufts:UA005.040.010.00001
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