Removal of Sulfamethoxazole in Secondary Effluent via Coupled Biofilm Slow Filtration and Nanofiltration: Effect of pH and the Mechanism of Membrane Contamination

Sulfamethoxazole (SMZ), a sulfonamide antibiotic, has been used in large quantities and is frequently detected in the secondary effluent of wastewater treatment plants. This poses a risk for the reuse of reclaimed water, making it necessary to implement a deep treatment process after secondary effluent in order to reduce the concentration of SMZ. In this article, we investigated the efficacy and mechanisms of the biofilm slow filtration–nanofiltration (NF) combined process for the removal of pollutants in secondary effluent. We explored the effects of different pH values on the removal of SMZ by this combined process and analyzed the interfacial mechanisms of pollutants with different surface properties and the surface of the NF membrane. The experimental results showed that at pH 8, the combined process exhibited the best removal efficiency for SMZ, achieving a maximum removal rate of 96.9%. The biofilm on the surface of slow filtration was composed of a relatively high proportion of beneficial microorganisms, including Ascomycetes, Acidobacteria, Mycobacterium, narrow-feeding Aeromonas, Dokdo, and Nitro spiraea, which play a positive role in the degradation of SMZ. During the NF membrane filtration process, both early and late stages of filtration indicated that a lower influent pH resulted in more severe membrane fouling. Conversely, higher influent pH values correlated with lighter membrane contamination.