| The Shortcut Simultaneous Nitrification and Denitrification(SSND)process is a new biological nitrogen removal process based on nitritation-denitrification and simultaneous nitrification-denitrification processes.Compared with the conventional nitrogen removal process,it has the advantages of saving aeration,less denitrification carbon source consumption,low sludge production and so on,which is suitable for treating low C/N wastewater.However,the startup of SSND process is not easily,and the process is difficult to keep stable operation with conventional control strategy.In order to study the real-time control strategy of startup and operation for SSND,one SBR reactor was applied to treat simulated wastewater with low ratio of COD to ammonium(C/N=4),and investigating the control method for improving the nitrogen removal efficiency by considering the process configuration and influence factors.(1)Under the condition of influent without of organic carbon,SBR was operated with controlled parameters and realized the nitritation-denitrification startup.Then launched SSND process with keeping the same controlled parameters and adding organic carbon in the influent.The results indicated that nitritation-denitrification process was started successfully by controlling pH was 8.0,temperature was 29.5±0.5℃,dissolved oxygen(DO)was 0.5 mg/L,ammonium concentration was between 50 and 75 mg/L and without organic carbon addition.During the aeration phase,the end-point of aeration was automatically controlled by the first derivative of DO.The stable nitritation process was achieved on the 30th day,and NAR remained above 91%.After that,the influent with organic carbon(C/N=4)was fed into SBR,and SBR was operated by real-time control.The total nitrogen concentration of outlet was around 38 mg/L,and the nitrogen removal efficiency(NRE)reached 45%,which indicated that the SSND process was started.(2)In order to increase the NRE of SSND,the SBR operation configuration was optimized by investigating the influence of aeration/non aeration ratio and batch feeding.The results showed that SSND had a better performance with the aeration/non aeration ratio of 2:1.The NRE was about 70%,and TN concentration was around 20 mg/L in outlet.Reducing the aeration/non aeration ratio could increase the nitrogen removal efficiency,but increase the length of SBR cycle.Furthermore,with the same influent concentration and volume,more feeding batches was benefit to increasing NRE.SBR had the best NRE with feeding batch of 3,specifically,the TN removal efficiency was 81%,and TN was about 15 mg/L in effluent.When feeding batches was more than 3,the NRE was not increased obviously,moreover,the operation of SBR was more complicated.(3)For achieving more better NRE of SSND,the influence of aeration rate,C/N ratio,MLSS were studied.The results of batch tests indicated that the NRE was reached 61%when aeration rate was 1.0 L/min,and increased to 74%when C/N ratio raised from 2 to 8.When MLSS went up to 12 g/L,NRE of SBR was 72%,approximately.Therefore,under the automatically control of end-point of aeration by the first derivative of DO,the NRE of SBR could reach around 90%by increasing MLSS higher than 10 g/L,and maintaining aeration rate at 1.0 L/min.(4)The results of microbial sequencing showed that the population structure of microorganisms and the abundance of dominant species were changing during the conversion process from nitrification to SSND.The species diversity of microorganisms is decreasing,which indicated that long-term reactor operation would reduce the diversity and abundance of microorganisms and made the population develop towards to single and specific function.The abundance of Nitrosomonas increased,while Nitrospira decreased to undetected.As the typical bacterial genus of heterotrophic nitrification-aerobic denitrification,Paracoccus became the dominant microorganisms.The results verified that the real-time control strategy was benefit to start SSND in SBR and maintain the stable operation. |
PDF Full Text Request