The Effect Of Sulfadiazine At Environmentally Relevant Concentrations On Aerobic Granular Sludge And Its Removal Mechanism

The wide use of antibiotics in human life and breeding industry lead more and more residual antibiotics in the evironment,which has aroused the concern of the whole society.Due to the low concentration and antiseptic qualities of antibiotics in the environment,it is not easy to remove antibiotics completely by traditional wastewater biological treatment process.Therefore,removal of antibiotics in the environment has always been a hot topic in environmental research.Aerobic granular sludge,which is a new self-assembly biological treatment technology,occupies an important position in the field of refractory wastewater treatment because of its compact structure,high biomass and impact resistance ability to toxic substances.This paper cultivated flocculent activated sludge in four identical sequencing batch reactor(SBR,R0-R3)and added different environmentally relevant concentrations of sulfadiazine to R1-R3(10.100,1000ppb respectively),with the purpose to explore the effect of sulfadiazine on formation process,physical and chemical properties,reactor performance,microbial community and the resistance genes of aerobic granular sludge.Finally we used the aerobic granular sludge to degrade sulfadiazine and analyze the degradation mechanism.The main research results are as follows:(1)Physical and chemical properties of sludge:sulfadiazine of different environmentally relevant concentrations has no inhibitory effect on granulation,on the contrary the granular sludge particle size and biomass presented larger and higher in the higher-sulfadiazine-concentration reactor.Meanwhile,with the increase of sulfadiazine concentration,the specific gravity,settling rate,and integrity coefficient of granular sludge also increase accordingly.Compared with the control group,after adding the sulfadiazine,extracellular polymeric substance concentration increased significantly in the experimental reactor,and the higher sulfadiazine concentration led the higher increase.(2)Reactor performance:results suggested that sulfadiazine decreased the COD and NH4+-N removal rate of aerobic granular sludge.However,the performance of reactors gradually restored as run time went by,finally reached the normal level(removal rate?90%).After 60th day,sulfadiazine removal rate achieves above 90%in R1-R3.It could be speculated that the microorganism in aerobic granular sludge was gradually domesticated under long-term sulfadiazine pressure.(3)Gene level:the qPCR results of sulfa resistance genes Sul-1 and Sul-2 suggested that sulfadiazine of higher concentration led more enrichment of the resistance genes.Meanwhile 16S rRNA sequencing analysis results showed that sulfadiazine decreased the biodiversity of sludge,screened bacteria and enriched some bacteria such as Nitrosomonas.The PICRUSt analysis results showed that sulfadiazine influenced the abundance of some functional genes such as transporters,ABC transporters and secretion system,which could help bacteria change their metabolism to adapt to the antibiotic pressure environment.(4)The degradation of sulfadiazine:A series of batch experiments proved that the degradation of sulfadiazine mainly happened in the process of nitration and COD degradation at aerobic conditions.Accordingly,it was speculated that AOB,NOB and aerobic HB played the major role to the degradation of sulfadiazine.