Enhanced migration and degradation of nitrobenzene in heterogeneous porous media using pulsed direct current electrical resistance heating with hydraulic circulation

Abstract

Electrical resistance heating (ERH) is a promising in-situ technology for heterogeneous organic contaminated site remediation, yet may have low efficiency when treating semi-volatile organic contaminant (SVOC) of relatively high boiling point. Herein, we chose nitrobenzene as a representative SVOC, and proposed an ERH system powered by pulsed direct current (PDC) with simple hydraulic circulation for improved remediation efficiency in heterogeneous media. The proposed PDC-ERH with hydraulic circulation showed overall improvement in heating performance and energy efficiency, as well as migration and removal of nitrobenzene. This new system improved the uniformity of PDC heating and achieved a temperature increase of ∼15°C compared to that using conventional alternating current (AC) of same voltage. Nitrobenzene migration out of the low permeability zone (LPZ) was intensified by the dual effects of heat-induced diffusion enhancement and electric field-induced electroosmotic flow, while subsequent removal was enhanced by electrochemical degradation and volatilization. After 96 h, the proposed system has a higher nitrobenzene removal from LPZ (> 97.1%) compared to that using AC (84.0%–95.9%). These results suggest PDC heating coupled with hydraulic circulation was a promising approach for heterogeneous site remediation.

Keywords

• Pulsed direct current
• Heterogeneous site remediation
• Electrical resistance heating
• Hydraulic circulation
• Contaminant migration