Intensified sulfamethoxazole removal in an electrolysis-integrated tidal flow constructed wetland system

This study aims to investigate the removal efficiency and mechanism of sulfamethoxazole (SMX) and fate of corresponding sul genes in an electrolysis-integrated tidal flow constructed wetland system (EC-TFCWs). Compared with the single-stage TFCWs, excellent SMX removal was obtained in EC-TFCWs (increased by nearly 20%) owing to synergistic effect of electrolysis-integrated microbial degradation and flocculation. However, SMX removal in EC-TFCWs can be affected by electrode materials with iron electrode higher removal (average removal efficiency = 81.86%) than that of graphite electrode (average removal efficiency = 77.83%). In addition, the removal efficiency of SMX increased from 65.52% to 84.23%, from 42.32% to 87.22% and from 66.33% to 91.9% with the increase of current intensity from 0.21 mA cm 2 to 1.50 m A cm 2 , hydraulic retention time (HRT) from 6 h to 48 h and electrolytic time from 2 h to 8 h, respectively. This result indicated that the current intensity, electrolytic time and HRT played an important role in SMX removal. The absolute abundance of sul genes in zeolite and effluent in EC (iron)-TFCWs was lower than that of in TFCWs at long stress of SMX. However, iron sludge can become a reservoir of sul genes. A novel EC (iron)-persulfate-integrated TFCWs was developed to further improve the performance of EC (iron)-TFCWs (increased by nearly 10%), which achieved a better removal effect and lower abundance of sul genes than that of in EC (iron)-TFCWs, and SO 4 − played a key important role.