| Aerobic granular sludge technology has been proven to be an emerging technology for efficient treatment of saline wastewater.Aerobic granular sludge technology has many advantages such as low operating costs,high load tolerance,and high biomass.However,the aerobic granular sludge inoculated by activated sludge usually has the disadvantages of unstable structure and low carbon and nitrogen removal efficiency under salt stress.In this study,anaerobic granular sludge was used as the inoculum.Through the cultivation strategy of "strengthen nitrogen removal followed by domesticate salt tolerance",the cultivation process of the salt-tolerant aerobic granular sludge for simultaneous nitrogen and carbon removal was studied and its performance was tested.The results showed that after 132 days,salt-tolerant aerobic granular sludge capable of simultaneous nitrogen and carbon removal was successfully obtained.Throughout the cultivation process,the structural properties and settling properties of the granular sludge did not change significantly.At 1%salinity,more than 90%of carbon removal and 90%of total nitrogen removal were achieved,denitrification process was the bottleneck step at this time,and NO3--N was high in the effluent;At 2%and 3%salinity,more than 90%of carbon removal and 75%of total nitrogen removal could be still maintained,nitrification process gradually became the bottleneck step,and a small amount of NO2--N accumulated.High-throughput sequencing of 16S rRNA genes analysis showed that salinity significantly reduced the abundance and diversity of microbial community,and the dominant abundance genus succeeded from Candidatus_Competibacter to Vitellibacter and Xanthomarina.The nitrogen removal functional bacteria in the salt-tolerant aerobic granular sludge are ammonia oxidizing bacteria Nitrosomonas and denitrifying bacteria Defluviimonas,respectively.The abundance of nitrite oxidizing bacteria is low,indicating that the salt-tolerant aerobic granular sludge may achieve the process of nitrogen and carbon removal through short-cut nitrification denitrification.The qPCR results showed that under high salt conditions,the relative abundance of the nitrite oxidation gene nxrB and the nitrite reduction gene nirS,nirK are low,which is the cause of the accumulation of NO2--N in the effluent.The results of this study can provide theoretical support for the cultivation of salt-tolerant aerobic granular sludge for simultaneous nitrogen and carbon removal. |
