Constructed wetlands (CWs) had been widely used to treat the tailwater from sewage treatment plants. However, the enduring effectiveness of CWs was still unclear. Therefore, this study aimed to investigate the chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and total phosphorus (TP) removal efficiencies (RE) of the Hongze CW (HZ-CW) after multi-years’ operation. The average COD RE were 7.6% and 15.14% in the 4th and 5th year, respectively. The NH₄⁺-N RE was 78.33% and 46.04% in the 4th and 5th year, respectively, while the TP RE remained high at 66.86% and 64.68%. The high-throughput sequencing analysis revealed that the bacterial community of HZ-CW at the end of the 5th year exhibited a substantial abundance and diversity, and Proteobacteria and Bacteroidota were the dominant phyla with a relative abundance of 33.75–71.8% and 11.28–24.53% in different zones of HZ-CW. Ammonia oxidizing organisms (AOMs) presented much higher relative abundance (0.43–0.79%) in aerated pond (AP) and four free water surface flow CWs (FWS1–FWS4) than those of anammox bacteria, indicating the dominant role of nitrification in NH₄⁺-N removal.

To resolve membrane fouling in the ultrafiltration process of sewage effluent, the impact of activated carbon catalytic ozonation (AC/O₃) on fouling control was investigated. The influence of initial pH on AC/O₃ for fouling alleviation was further explored. The results revealed that AC/O₃ pretreatment greatly mitigated the membrane fouling. The total fouling, reversible fouling, and irreversible fouling were all decreased. The initial pH influenced the alleviation effect of AC/O₃ on fouling control obviously, although it only slightly impacted the AC adsorption pretreatment on fouling alleviation. Besides, there was no obvious impact of pH on the ultrafiltration process. Compared with the adjustment of initial pH during ultrafiltration and the pretreatment methods such as AC adsorption and preozonation, AC/O₃ displayed the greatest effect on both fouling alleviation and permeate quality improvement under all pH conditions. It was the component transformation of sewage effluent after AC/O₃ pretreatment that caused the alleviation of membrane fouling. With the increase in initial pH, the high-MW biopolymers as well as humic substances in the effluent organic matter could be preferentially removed by AC/O₃, which mitigated the flux decline during the ultrafiltration process and decreased the reversible and irreversible fouling.