Social network of filamentous Sphaerotilus during activated sludge bulking: Identifying the roles of signaling molecules and verifying a novel control strategy

Abstract

Filamentous bulking is a common problem in wastewater treatment plants (WWTPs), resulting in poor sludge settleability and bad effluent quality. Existing control methods generally kill filaments at the cost of destroying the floc structures, due to the lack of knowledge on microbial interactions. Filamentous bulking is essentially an abnormal filamentous evolution depending on the sophisticated communication between floc-formers and filaments mediated by signal molecules (SMs). This study firstly identified 3-OH-C10-HSL (237 suspended solids (SS)) to drive Sphaerotilus bulking, and a quorum quenching (QQ) technology precisely inhibited bulking occurrence with maintaining floc stability and excellent bioactivity. The social network was established to clearly reveal the interacting communication between Sphaerotilus and its neighbors release functional SMs. It was further discovered that 3-OH-C10-HSL activated the signal receptor luxR of Sphaerotilus, and following up-regulated the transcriptional expressions of gluconeogenesis pathway and flagellum assembly (1.07–7.77-fold). As expected, adding its analogue 3-OXO-C10-HSL effectively quenched Sphaerotilus’ abundance<0.27 %, and decreased sludge volume index (SVI) below 150 mL/g. The morphology features and surface properties were both restored to the normal level, and specific oxygen uptake rate (SOUR) was improved by 26–35 % than that in the non-bulking sludge. This study improves our understanding of filamentation mechanisms, and represents progress towards the development of precise anti-bulking strategies.