Acceleration Of Pyridine-degrading Aerobic Granuler Sludge Based On Coaggregation

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 to be combined for further experiment.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.It was chosen as inocula for acceleration of pyridine-degrading aerobic granuler sludge.The investigation of the coaggregation mechanism indicated that high concent of c-di-GMP promoted aggregation by promoting the secretion of PS,further promoting the acceleration of aerobic granules.In this study,three identical SBR bioreactors were set up and kept running under exactly the same conditions.Their inocula were NJUST18,NJUST29 and NJUST18+NJUST29,with the same amount.They were named as R1,R2 and R3,respectively.After 20d's cultivation,3000 mg/L pyridine could be completely degraged in R3 in 12h with the best effectiveness of mineralization,as well as effulents of R1 and R2 containing over 600 mg/L pyridine.Some visible aerobic granules could be seen in R3 in 27 days.After 42 days cultivation,all the sludge in R3 became aerobic granular sludge with the grain diameter of 0.5-1.5 mm.However,sludge in R1 and R2 remained flocs during the whole cultivation period of 62d,the only variation is flocs getting larger.R1 and R2 showed no indication of granulation.R3 also presented the higher EPS and c-di-GMP contents than R1 and R2,of 282.31 mg/gMLSS and 1464.00 mg/gMLSS respectively,corroborated the mechanism of coaggregation between NJUST18 and NJUST29 promoting secretion of c-di-GMP and PS then making further efforts in promoting aggregation to accelerate aerobic granulation.This study demonstrated that bacterial combinations as inocula could accelerate aerobic granulation and had promising potential for the treatment of industrial wastewater.