Degradation of antibiotics and profiling of transformation products upon peracetic acid-mediated treatment of electrochlorinated groundwater in a flow-through reactor.

Preventing the formation of hazardous chlorinated transformation products (Cl-TPs) when applying the electrochemical advanced oxidation processes (EAOPs) is a major challenge for ensuring their broader scale-up. In this context, the addition of peracetic acid (PAA) can potentially contribute to reduce the risk of Cl-TPs, but the associated transformation pathways remain insufficiently understood. Here, PAA-mediated electrochlorination process was found to reduce typical Cl-TPs (e.g., chloroform below 60 μg L-1) by 26.9 %∼80.8 %. Under optimized conditions, an innovative PAA-based treatment in a single-pass flow-through electrochemical reactor achieves the removal of four mixed antibiotics with low specific energy consumption (5.3 Wh mmol-1). The antibiotics concentration in the effluent remained below the detection limit within 10 operation cycles. In addition, reductions in Cl-TPs were achieved in both simulated and actual groundwater, meeting the 2022 Chinese drinking water quality standards. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that PAA-based electrochlorination preferentially removed highly unsaturated heavy byproducts (O/C < 0.3, MW >400 Da), and the CHOCl formulae number decreased by 59 %. The transformation pathways of Cl-TPs were mainly identified as decarbonylation, dihydroxylation, and hydrogenation. Moreover, the possible halogenation pathways number showed a significant decrease of 77.9 %. These findings provide deeper insights into the degradation mechanisms and Cl-TPs minimization during PAA-mediated electrochemical antibiotic degradation, shedding light on the transformation processes in diverse environmental scenarios.