Response of extracellular polymeric substances in algal-bacterial granular sludge under salinity stress: Secretion behavior, structural properties, and protective roles.

The algal-bacterial granular sludge (ABGS) technology exhibits the advantages of low energy consumption and high shock load resistance. While ABGS regulates extracellular polymeric substances (EPS) secretion to cope with adverse conditions, the role of EPS in resisting salinity stress remains uncertain. This study investigated the response ofEPS in ABGS to salinity stress (0-5 %) by examining secretion behavior, structural properties, and protective roles. The results showed that high salinity (≥3%) led to changes in the components and content of EPS. Additionally, analysis of the adhesion in EPS indicated that the frequency of tightly bound EPS (TB-EPS) decreased sharply from -10 Hz (0 %) to -45 Hz (1 %). According to the extended Derjaguin-Landau-Verwey-Overbeek theory and the rheological properties, TB-EPS significantly influences sludge flocculation and stability at low salinity. This study provided a scientific foundation for revealing the role mechanism of EPS in ABGS for saline wastewater treatment.