Potential role of AHL-mediated quorum sensing in inducing non-filamentous sludge bulking under high organic loading

The underlying microcosmic mechanisms of non-filamentous bulking is still unclear. Non-filamentous bulking usually occurs under abnormal operating conditions (adverse environmental conditions for bacteria). Microbes coordinate their behaviors in response to adverse environments through quorum sensing (QS). The potential role of the QS in inducing non-filamentous bulking and the feasibility of maintaining sludge aggregate structure, stability, and settleability through the quorum quenching strategy were investigated in this study. The results indicated that the concentration of N-acyl homoserine lactose (AHL) obviously increased and the synthetic gene hdtS and the sensing gene lasR related to AHLs were significantly upregulated in the sequencing batch reactor (SBR) under the high organic loading. The AHL-QS system was triggered, which indued non-filamentous bulking in the SBR. The production of exopolysaccharide was evidently promoted by QS via regulating the pel gene cluster, resulting in an increase in the negative charge and a decrease in the hydrophobicity on aggregate surface. The surface energy barrier (WT) between bacteria significantly increased during non-filamentous bulking. Additionally, the triggered QS resulted in a decrease in the molecular weight of exopolysaccharides, which led to the weakening of gel properties. Vanillin as a quorum sensing inhibitor effectively inhibited non-filamentous bulking by decreasing the production of exopolysaccharides, without the negatively effect on the key enzyme activity of nitrogen removal and wastewater treatment performance. Therefore, quorum quenching is the potentially effective strategy to prevent and control non-filamentous bulking. This study provided new insight into the microcosmic mechanism of non-filamentous sludge.

Automated summary

The underlying microcosmic mechanisms of non-filamentous bulking are still unclear, and quorum sensing is a potentially effective strategy to prevent and control non-filamentous bulking.