Bidirectional regulation of aerobic granular sludge through diffusible signal factor/bis(3'-5')-cyclic dimeric guanosine monophosphate crosstalk: Restoring stability and enhancing maturation at low temperatures.

Low temperatures destabilize aerobic granular sludge (AGS). While bis(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) regulates AGS formation and stability, interactions between diffusible signal factor (DSF) and c-di-GMP suggest DSF-mediated regulatory strategies. However, its feasibility at low temperatures remains unclear. In this study, two functionally compromised AGS systems were investigated at 10°C. In R1, the addition of DSF reduced c-di-GMP concentration by 64 %, mitigating excessive extracellular polymeric substances (EPS) production, and restoring pollutant removal efficiency. Conversely, in R2, the addition of salicylic acid (SA) increased AGS particle size from 658 to 952µm, accompanied by a 20 % rise in c-di-GMP concentrations. Suppression of filamentous (e.g., Sphaerotilus (5 % to 2 %)), correlated with reduced EPS synthesis in R1. Increased abundances of c-di-GMP producing genus, (e.g., Thauera (3 % to 5 %)) demonstrated that SA inhibited DSF activity in R2. These findings present a novel framework for regulating of AGS-based wastewater treatment at low temperatures.