Enhancing DNAPL removal from low permeability zone using electrical resistance heating with pulsed direct current

Area of Science:

• Environmental Engineering
• Remediation Technologies
• In-situ Heating

Background:

• Electrical resistance heating (ERH) is effective for contaminant remediation, particularly in heterogeneous sites with low permeability zones.
• Conventional ERH using alternating current (AC) often requires high energy input, leading to low energy efficiency.
• Dense nonaqueous phase liquids (DNAPLs) pose challenges in low permeability zones, necessitating improved remediation strategies.

Purpose of the Study:

• To introduce and evaluate pulsed direct current (PDC) as an energy-efficient alternative to AC for ERH.
• To investigate the effectiveness of PDC in enhancing DNAPL migration and remediation in low permeability environments.
• To demonstrate the proof-of-concept for PDC-enhanced ERH in a lab-scale heterogeneous system.

Main Methods:

• A lab-scale, two-dimensional heterogeneous sand system (40 cm × 30 cm) was utilized.
• Trichloroethylene (TCE) DNAPL was introduced into the central low permeability zone.
• PDC, generated by current rectification, was applied and compared against conventional AC under identical voltage gradients.

Main Results:

• PDC application resulted in a faster temperature increase compared to AC at the same voltage gradient.
• TCE removal efficiency increased significantly with PDC, reaching 89.6% at a 3.75 V cm^-1 voltage gradient, compared to 9.4-91.1% for AC.
• PDC demonstrated a 27.8% lower energy consumption (390 kWh kg^-1) compared to AC at a 3.5 V cm^-1 voltage gradient.

Conclusions:

• Pulsed direct current (PDC) is a promising approach to enhance the energy efficiency of electrical resistance heating (ERH).
• PDC application improves DNAPL migration and remediation effectiveness in low permeability zones.
• The findings support PDC as a viable and more efficient alternative to AC for ERH contaminant remediation.