Triggering rapid generation of singlet oxygen in novel series-connected redox-electrodialysis for efficiently removing refractory pharmaceuticals from wastewater

Efficient degradation of recalcitrant pharmaceuticals in wastewater from coastal areas is one of the challenges in the field of water treatment. Here, we present a synergistic redox-electrodialysis via series-connected strategy to efficiently remove refractory pharmaceuticals by utilization of NaCl in seawater and dissolved oxygen in wastewater without additional chemicals. The constructed process realized 100 % degradation of 100 mg/L ampicillin (AMP) at 4 V, and represented a high selectivity for AMP degradation with coexistence of high-concentration natural organic matter, small-molecule organic acids and inorganic salts. The process was also highly effective in removing other various pharmaceuticals including tetracycline, ciprofloxacin and levofloxacin. Radical scavenging experiments, EPR testing and competitive kinetic results confirmed both ¹O₂ and •OH are the main reactive species for AMP degradation, whose respective contributions are 60.7 % and 39.3 %. Mechanism studies indicated series connection of anode and cathode chambers triggered the transient activation of in-situ generated hydrogen peroxide by anodic production of HClO to form ¹O₂. The possible degradation pathways of AMP underwent the CN bond breaking, β-lactam ring opening, deamination, hydroxylation, decarbonylation and decarboxylation reactions. The reduced toxicity of the treated wastewater was confirmed by ECOSAR program and zebrafish experiments. In addition, the proposed process also realized 100 % AMP degradation in real wastewater with simultaneous 90 % desalination of real seawater.