Accelerated performance recovery of anaerobic granular sludge after temperature shock: Rapid construction of protective barriers (EPS) to optimize microbial community composition base on quorum sensing

Poor temperature shock resistance of anaerobic granular sludge (AnGS) is one of its main disadvantages. In this study, enhancing the temperature shock resistance of AnGS by regulating quorum sensing (QS) based on the exogenous addition of N-acyl homoserine lactones (AHLs) was investigated, and the regulatory mechanism of AHLs-mediated QS based on extracellular polymeric substances (EPS) action in AnGS was revealed. The results indicated that adding 10 μM AHLs significantly enhanced the COD removal (increased by 9.3 ± 1.2%) and specific methanogenic activity (increased by 15.2 ± 3.6%) of AnGS after temperature shock, and the recovery time was reduced by 4 days. The sludge breakage and particle size reduction induced by temperature shock were attenuated by AHLs-mediated QS. Meanwhile, exogenous AHLs increased EPS concentration and the number of hydrophobic functional groups in AnGS. The addition of 10 μM AHLs reduced the ratio of Firmicutes to Bacteroidota (decreased by 0.17 ± 0.01), leading to higher microbial community stability. The enrichment of major functional bacteria (Bacteroidota, Desulfobacterota and Firmicutes) and hydrogenotrophic methanogens (Methanothermobacter and Methanobacterium) was promoted by 10 μM AHLs. The increased EPS induced by AHLs provided the protection for microbial community optimization, leading to the rapid recovery of the temperature-shocked AnGS performance. This study provided a new comprehensive insight into the regulatory mechanisms of AHLs-mediated QS in AnGS.