Comparison between donor substrates for biologically enhanced tetrachloroethene DNAPL dissolution.

Area of Science:

• Environmental Science
• Environmental Engineering
• Microbiology

Background:

• Tetrachloroethene (PCE) dense nonaqueous-phase liquid (DNAPL) represents a persistent groundwater contamination challenge.
• Biologically enhanced dissolution offers a promising strategy to reduce DNAPL longevity.
• Previous studies indicated potential for bioenhanced DNAPL dissolution.

Purpose of the Study:

• To evaluate various donor substrates for bioenhanced DNAPL dissolution.
• To compare different remediation strategies for PCE DNAPL.
• To investigate the impact of substrates on degradation products and microbial activity.

Main Methods:

• Columns were set up with PCE DNAPL and different donor substrates: pentanol (continuous feed), calcium oleate (initial placement), and olive oil (initial mixture).
• A control column without substrate was used for comparison.
• DNAPL dissolution rates, degradation products (e.g., cis-DCE, VC, ethene), and microbial activity (methanogenesis) were monitored.

Main Results:

• DNAPL dissolution rates were approximately three times higher in columns with substrates compared to the control.
• cis-DCE was the major degradation product, with varying amounts of VC and ethene observed.
• Methanogenesis, which inhibited PCE transformation, occurred in pentanol and oleate columns but not in the olive oil column.
• Presaturating pentanol feed with PCE significantly reduced detrimental methane production.

Conclusions:

• Donor substrates can significantly enhance PCE DNAPL dissolution rates when coupled with biological transformation.
• The choice of substrate influences degradation pathways and the extent of competitive methanogenesis.
• Olive oil appears to be a promising substrate for enhancing dehalogenation while mitigating methanogenesis.
• Strategies like presaturating feeds can help control methane production in bioenhanced remediation.