Enhanced removal performance of estriol by a three-dimensional electrode reactor

•TDER performed much better in removing E3 than two-dimensional electrode reactor.•The possible degradation mechanisms of E3 were demonstrated.•Two new E3 degradation intermediates were observed for the first time.•Continuous-flow TDER achieved an 80% E3 removal efficiency with proper conditions.

This study dealt with the treatment of estriol (E3), a typical endocrine disrupting chemical (EDC), using a three-dimensional (3D) electrode reactor (TDER). The reaction rate per unit area of TDER in batch mode was 3.23-5.75 times that of a conventional two-dimensional (2D) electrode reactor, while its energy consumption was only 1/7-1/5 of that of the latter. The kinetics analysis results indicated that the degradation of E3 in both systems followed pseudo first-order kinetics. The effects of initial E3 concentration, current density, electrode distance, and recirculation flow rate on the performance of TDER were investigated in batch mode. A current density of 1.0 mA/cm2, electrode distance of 2 cm, and recirculation flow rate of 200 mL/min were identified as optimal operating parameters that could guarantee excellent E3 removal efficiency and energy consumption. Progesterone and 3à-hydroxy-5á-androstane-17-one were identified by UPLC/MS/MS and GC/MS for the first time as E3 degradation intermediates. A possible E3 degradation pathway was proposed based on the intermediates and the results of previous studies. The mechanism analysis results identified indirect oxidation as the main contributor to E3 degradation in batch TDER, with the repolarization of particle electrodes contributing to the degradation. Subsequently, TDER was operated in continuous-flow mode to treat a secondary effluent spiked with E3. With a hydraulic retention time of 50 min and a current density of 20 mA/cm2, TDER achieved an E3 removal efficiency of 80%, thereby demonstrating the ability of continuous-flow TDER to produce a stable, high quality effluent. The aforementioned results highlighted 3D electrolysis as a promising alternative method for removing trace EDCs from secondary effluent in pretreatment or advanced treatment applications.

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