Potential negative effects of illumination on gravity-driven membrane system in treating sulfamethoxazole-containing water

Sunlight illumination could affect the stability and sustainability of the gravity-driven membrane (GDM) system. In this study, sunlight-based GDM and GDM were compared to treat sulfamethoxazole (SMX)-contained water. Results indicated that the removal of DOC, SMX and fluorescent pollutants became worse due to the bacteria activity limited by algae proliferation in sunlight-based GDM. But the total phosphorus (TP) removal rate increased by 74.72% due to algal assimilation. Algae promoted a thick and sticky biofilm with enrichment of extracellular polymeric substances (EPS), and the biofouling layer possessed the highest fluorescence intensity of pollutants. Long-term illumination reduced the biodiversity and richness in the biofouling layer. Pseudomonas was dominant in the sunlight-based GDM (71.3%), while Acinetobacter and Saccharimonadales were more prevalent in the GDM blank, which were related to SMX degradation. Besides, algae reduced the degradation pathways of SMX. Considering the application of GDM in rural areas, long-term illumination should be avoided.