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

Electrical resistance heating (ERH) has been widely applied for contaminant remediation in heterogeneous sites especially when low permeability zones exist, yet requires high energy input. To address the low energy-efficiency of ERH using conventional alternating current (AC), pulsed direct current (PDC) obtained by current rectification was introduced for heating to enhance dense nonaqueous phase liquid (DNAPL) migration in low permeability zones. Here we showed the proof-of-concept in a lab-scale two-dimensional heterogeneous sand system (40 cm × 30 cm) with trichloroethylene (TCE) DNAPL in the central low permeability zone. Applying PDC achieved faster temperature increase compared to that with the conventional AC of the same voltage gradient. The overall TCE removal efficiency from the cell increased from 79.0% to 89.6% with increasing PDC voltage gradient from 3 to 3.75 V cm-1, compared to that of 9.4-91.1% with conventional AC. The lowest energy consumption of PDC was 390 kWh kg-1 at a medium voltage gradient of 3.5 V cm-1, which was 27.8% lower compared to that with AC at the same voltage gradient. These results suggest that remediation using pulsed direct current is a promising approach to improve the energy-efficiency and effectiveness of ERH.