Noncontact Treatment of Contaminated Groundwater: Graphite-Mediated Long-Distance Electron Transfer from Contaminants...

In situ chemical oxidation (ISCO) has been widely used in groundwater remediation, whereas the injected chemicals pose secondary risks to the remediated aquifers. Here, we propose a noncontact oxidation scheme in which contaminants are treated by physically separated oxidants through wired electrodes, thereby eliminating the injection of chemicals into the aquifer. Groundwater circulation is applied to transport contaminated groundwater from surrounding aquifers to the in-well electrode. We serendipitously found that graphite electrodes after simple preoxidation showed superior performance to other commercial electrodes, exhibiting high and sustainable performance in mediating the long-distance electron transfer from contaminants to oxidants. For the noncontact oxidation of 10 μM phenol by 10 mM peroxysulfate (PDS), the removal reached 85% within 2 h and was maintained stable over 10 consecutive treatment cycles. Persulfate led to a larger contaminant removal than other common oxidants. Assisted with hydraulic circulation, this system achieved 95% of phenol removal within 36 h in a simulated aquifer. Contaminants with high electron-donating abilities were prone to be oxidized. Anode/contaminant and cathode/oxidant interfacial interactions played a critical role in noncontact oxidation. This noncontact oxidation strategy presents a new horizon for green groundwater remediation.