Increasing electron donor concentration does not accelerate complete microbial reductive dechlorination in...

Area of Science:

• Environmental Science
• Microbiology
• Geochemistry

Background:

• Chloroethene contamination poses significant environmental and health risks.
• Microbial reductive dechlorination is a key process for remediating chloroethene-contaminated sites.
• Electron donor addition is a common strategy to enhance reductive dechlorination.

Purpose of the Study:

• To investigate the impact of electron donor addition and concentration on the reductive dechlorination of trichloroethylene (TCE) and vinyl chloride (VC).
• To compare the effectiveness of different types of electron donors, including acetate and lipid-based substrates.
• To evaluate the influence of electron donor stoichiometry on dechlorination rates and extents.

Main Methods:

• Incubation of chloroethene-contaminated sediment with various electron donors at different concentrations (1x and 10x stoichiometry).
• Monitoring of TCE, VC, and ethene concentrations over time to assess dechlorination progress.
• Analysis of microbial activity, including reductive dechlorination and methanogenesis.

Main Results:

• Unamended controls achieved complete TCE to ethene dechlorination within 79 days.
• Addition of acetate and high molecular mass substrates did not consistently enhance dechlorination and sometimes hindered it.
• Increased electron donor concentrations (10x) generally did not improve dechlorination rates and could favor methanogenesis over dechlorination.

Conclusions:

• Electron donor addition does not universally accelerate reductive dechlorination and can increase remediation costs.
• Higher electron donor concentrations than stoichiometrically required may inhibit complete dechlorination.
• Site-specific evaluation of electron donor demand is essential, and monitored natural attenuation may be the most favorable approach in some cases.