Coaggregation mechanism of pyridine-degrading strains for the acceleration of the aerobic granulation process

In this study, the aggregation of nine pyridine-degrading strains was investigated for the acceleration of the aerobic granulation process, with emphasis on the coaggregation mechanisms involved. Rhizobium sp. NJUST18 and Shinella granuli NJUST29 (with strong aggregation ability but with relatively poor pyridine degradation ability) and Paracoccus versutus NJUST32 (with strong pyridine degradation ability but with poor aggregation ability) were chosen as inocula for aerobic granulation. The combination of NJUST18 + NJUST29 demonstrated more powerful coaggregation abilities and comparable pyridine-degrading ability compared with NJUST18 + NJUST32, NJUST29 + NJUST32 and the individual strains. The investigation of the coaggregation mechanism indicated that the combination of NJUST18 + NJUST29 presented the highest extracellular polymeric substances (EPS) content of 232.79 mg gVSS(-1) and the second messenger cyclic diguanylate (c-di-GMP) content of 268.56 mg gVSS(-1), making the combination beneficial for aerobic granulation. In the sequential batch reactors (SBRs) inoculated with the combination of NJUST18 + NJUST29, aerobic granules with diameter of 0.2-0.5 mm was formed after operation period as short as 42 days, demonstrating that the combination of NJUST18 + NJUST29 as inocula in aerobic granulation system had promising potential for the treatment of high-strength pyridine wastewater.