Density-modified displacement for dense nonaqueous-phase liquid source-zone remediation: density conversion using a...

Area of Science:

• Environmental Science
• Geochemistry
• Chemical Engineering

Background:

• Dense nonaqueous-phase liquids (DNAPLs) are persistent groundwater contaminants.
• DNAPL remediation is challenging due to potential downward migration.
• Surfactant-enhanced aquifer remediation (SEAR) offers a promising solution.

Purpose of the Study:

• To investigate the density conversion of chlorobenzene (CB) and trichloroethene (TCE) using n-butanol (BuOH).
• To assess the feasibility of density-modified displacement (DMD) for DNAPL remediation.
• To understand the phase behavior and composition changes of DNAPLs with BuOH.

Main Methods:

• Batch experiments were conducted to analyze NAPL composition, density, and phase behavior.
• Ternary phase diagrams were developed for contaminant/BuOH/water systems.
• UNIQUAC calculations supported experimental data.
• Interfacial tensions were measured between NAPLs and BuOH solutions.

Main Results:

• Density conversion of CB and TCE occurred at BuOH mole fractions of 0.38 and 0.50, respectively.
• Water incorporation into the organic phase limited NAPL composition and density changes.
• Interfacial tensions decreased with increasing BuOH mole fraction but remained above 2.5 dyn/cm.
• Calculations indicated density conversion is achievable without premature NAPL displacement.

Conclusions:

• Density-modified displacement using n-butanol is a viable strategy for DNAPL remediation.
• The DMD method effectively reduces the risk of downward DNAPL migration.
• Understanding phase behavior is crucial for optimizing SEAR technology.