Electron donor limitations reduce microbial enhanced trichloroethene DNAPL dissolution: a flux-based analysis using...

Area of Science:

• Environmental Science
• Geochemistry
• Microbiology

Background:

• Microbial enhanced dissolution is a promising remediation strategy for chlorinated solvents like trichloroethene (TCE).
• Electron donor availability is a critical factor controlling the efficiency of microbial reductive dechlorination of TCE.
• Dense non-aqueous phase liquids (DNAPLs) represent a persistent source of groundwater contamination.

Purpose of the Study:

• To quantitatively investigate the relationship between electron donor supply rate and the enhancement of TCE DNAPL dissolution.
• To determine the conditions under which electron donor supply or dechlorination kinetics limit the dissolution enhancement.

Main Methods:

• Utilized diffusion cells with a sand layer separating a TCE DNAPL source from an aqueous layer.
• Amended the aqueous layer with varying concentrations of formate (0-16 mM) as the electron donor.
• Measured TCE diffusion flux and compared it to formate diffusion flux to assess limiting factors.

Main Results:

• TCE DNAPL dissolution rate increased with formate concentration, achieving a 2.4-fold enhancement at 16 mM formate.
• At lower formate concentrations (2-8 mM), TCE diffusion flux matched formate diffusion flux, indicating electron donor limitation.
• At 16 mM formate, TCE diffusion flux was less than formate flux, signifying that dechlorination kinetics became the limiting factor.

Conclusions:

• Electron donor concentration directly predicts DNAPL dissolution flux under electron donor-limited conditions.
• Dechlorination kinetics can limit the extent of DNAPL dissolution enhancement even with sufficient electron donor.
• Optimizing electron donor supply is crucial for effective microbial remediation of TCE DNAPLs.