Performance and bacterial characteristics of aerobic granular sludge in Check for response to alternating salinity

Salt concentration often fluctuates in influent industrial wastewater. The behavior of aerobic granular sludge (AGS) in response to the stress of alternating salt concentrations remains unclear. In this study, we ran six identical sequencing batch reactors to follow the performance and microbial characteristics of AGS under 1%, 2%, 4% salinity and corresponding alternating salinity, respectively. The results demonstrated that when compared with the control, alternating salinity not only increased the COD removal efficiency of the reactor significantly (p < 0.001) but also generated high concentration of granular biomass with good settling ability. Pearson correlation analysis indicated that the microorganism mostly used an intracellular second messenger molecule c-di-GMP to regulate extracellular polymer contents. Specifically, the increase of extracellular polysaccharide was conducive to the cohesive strength of the granules, resulting in higher biomass concentration and carbon removal efficiency. Additionally, microbial community analysis confirmed that the relative abundance of c-di-GMP pathway-dependent community, in particular Propionibacterium (24.4%-50.9%), was significantly more dominant under alternating salt conditions.