Research On Pivotal Techniques Of Simultaneous Shortcut Nitrification-Denitrification Based On Zoned Oxygen

In recent years,increasingly serious environmental problems have forced the effluent discharge standards of urban sewage treatment plants to increase continuously,especially for nitrogen and phosphorus pollutants that are highly prone to eutrophication of water bodies.The state has proposed a more stringent deep requirements for nitrogen and phosphorus removal than the first-class A standard.However,due to the widespread C/N ratio in urban sewage in China,it is necessary to strengthen the denitrification potential of the biological nitrogen removal system by adding carbon sources,which leads to great waste of resources.Based on this,based on the investigation of low C/N wastewater quality,this paper developed a set of improved oxygenation A²/O pilot-scale reaction device to study the feasibility of induced short-range nitrification under the combined control of zoned oxygen and aeration intensity.To analyze the effect of short-cut nitrification and denitrification on the nitrogen removal performance of the system,and to explore its mechanism of action.In addition,the activated sludge-biofilm composite system was constructed by adding suspended bio-filler to further study the effect of simultaneous nitrification and denitrification on biological nitrogen removal.The results show that the DO concentration in the aerobic zone is the main factor determining the type of nitrification relative to the proportion of the partition.When the DO in the aerobic zone is 2.0².5mg/L,the short-range nitrification cannot be achieved by adjusting the partition ratio.When the DO in the aerobic zone is0.5⁰.8mg/L,the short-range nitrification of the system changes significantly with the proportion of the system.Process parameters of optimal working conditions:DO=0.5⁰.8mg/L in aerobic zone,V_anaerobic:V_Aerobic is 1:1,the short-range nitrification rate reaches 62.6%,and the effluent TN drops to 10.5mg/L.Nitrogen efficiency is significant.Through the intermittent OUR method,the composition of the carbon source in the anoxic zone under various working conditions was analyzed.The results show that under optimal conditions,the COD consumption by short-cut nitrification and denitrification is reduced by 27.3%compared with the typical full-scale nitrification stage 1,and the biodegradable COD utilization rate in the anoxic zone is63.6%.The value is much higher than other stages;the utilization efficiency of carbon source in the anoxic zone is high,and the demand of short-range denitrifying carbon source is decreased,which are the key factors to ensure the low C/N ratio of biological nitrogen removal potential of sewage.In addition,the aeration zone under optimal conditions can meet the requirements of microbial intermittent aeration,so it is of great significance to improve the sedimentation performance of activated sludge.High-throughput sequencing showed that the relative abundance of AOB and NOB decreased by 7.3%and 57.9%under optimal conditions,indicating that the adjustment of partition ratio and DO concentration was more significant for NOB washing,resulting in the appearance activity of NOB is severely inhibited.Based on the short-range nitrification operation conditions,the activated sludge-biofilm composite system was successfully constructed by adding bio-filler in the aerobic zone.The biofilm growth on the surface of the carrier can be roughly divided into three stages.The biofilm is basically mature around 40d,and then dynamically balanced self-renewing growth,the biomass change is small,and it is stable at 40.05mg/g?according to VSS/Filling meter?.The biofilm microbial flora analysis showed that it had selective enrichment effect on AOB,the relative abundance of AOB was 2.84%,the relative abundance of typical denitrifying bacteria reached33.71%,and some anaerobic ammonia oxidizing bacteria were detected.Therefore,the ammonia nitrogen removal efficiency increased from 92.2%to 97.7%,the system short-term nitrification increased slightly,and the simultaneous nitrogen removal performance was significant.The SND efficiency increased from 21.6%in the initial film to 46.5%,and the TN removal rate reached 86.1.%,the effluent TN is stable below 8.0 mg/L.