Direct current driven persulfate delivery and activation for heterogeneous porous media remediation: Coupling effects of electric-thermal-chemical-flow fields

Direct current (DC) has promising potential for persulfate delivery and activation in heterogeneous site remediation, yet requires deeper understanding. Here, we investigated the efficiency of DC for persulfate delivery and activation and compared with alternating current (AC). While AC electric field only influenced persulfate fate by Joule heating effect, DC electric field induced electrokinetic migration of persulfate and contaminants, as well as promoted persulfate activation with Joule heating and electrochemical reactions. DC system achieved 95 % MCB removal which was 3.1 times of that in AC system using the same voltage input (60 V) with a velocity of 0.5 m/d. When the applied DC voltage increased from 20 V to 60 V (0.5–1.5 V/cm), persulfate activation pathway changed from electrode reactions to the coupled activation pathways of electrode, chemical and heat reactions, thus resulting in increasing MCB removal efficiency from 57 % (20 V) to 95 % (40 V and 60 V). The energy consumption with 40 V (11.6 kWh/g) was 2.6 times of that using 20 V (4.4 kWh/g), and dramatically increased to 11.7 times with 60 V (50.2 kWh/g). This study provides a new perspective on improving the efficiency of persulfate delivery and activation in heterogeneous sites remediation using DC-driven system.