Study On The Influencing Factors Of Short-cut Nitrification And Half-nitrification In Sequencing Batch Reactor

Novel biological nitrogen removal technology is a green and cost-effective technology,that has received much attention in the context of wastewater treatment,with the improvement of wastewater discharge standards.Due to the difference between ammonia oxidizing bacteria(AOB)and nitrite oxidizing bacteria(NOB)in physiological ecology,the accumulation of nitrite in the system can be achieved by inhibiting the activity of NOB.However,the stable accumulation of nitrite in biological systems can be affected by many factors,such as dissolved oxygen(DO),free ammonia(FA),temperature(T)and other factors.In this study,sequencing batch reactor(SBR)was inoculated ordinary activated sludge and used for short-cut nityification and half-nitrogenation.The effects of T,free ammonia concentration,DO and operating mode of the reactor on NOB inhibition were studied systematically and the key operational parameters regarding fast start-up and long-term stable operation of the system were identified.The microbial community structure within the system was analyzed by high-throughput sequencing technology,and the relationship between the operational effects of the process and the microbial community structure was discussed in detail.The main results of this study are as follows:(1)Under the conditions of influent ammonia nitrogen concentration 50mg/L,HRT was 12 h,influent p H was 7.5,DO concentration was 2~3mg/L,SBR reactor can complete the whole process nitrification of low ammonia nitrogen concentration influent water for 4 days,and no nitrite nitrogen accumulation can be achieved in the system.The highest removal rate of ammonia and nitrogen was 97%.(2)Ammonia nitrogen concentration increased to 200mg/L.temperature was 25±2?,p H was 7.5~8.2,DO concentration was 1~2mg/L,hydraulic retention time(HRT)was 22 hours,short-cut nitrification is completed in 21 days,the oxidation rate of ammonia nitrogen was 98%.The accumulation rate of nitrite nitrogen was 90%,and the inhibition intensity of FA and DO on NOB was FA > DO.(3)The ammonia nitrogen concentration of influent was reduced to 50mg/L,and the concentration of DO was decreased continuously.The ammonia oxidation rate and nitrite nitrogen accumulation rate were above 92% after 41 days of short-cut nitrification.A new type of nitrous ammonia oxidizing bacteria Nitrotoga,appeared during the operation of short-cut nitrification,but Nitrosomonas was the dominant bacteria in the system,and the content of Nitrosomonas was much higher than that of Nitrotoga,which was the essential reason for the realization of short-cut nitrification.(4)The long-term low dissolved oxygen concentration was the main reason to destroy the short-cut nitrification.Under the condition of low DO concentration for a long time,the short-cut nitrification was completely destroyed after 65 days of operation because the number of Nitrospira was much larger than that of Nitrosomonas,and the effluent nitrate nitrogen concentration was 27mg/L,and the nitrification rate of effluent was 27mg/L.The ammonia nitrogen concentration of effluent remained basically at 2mg/L.(5)The influent ammonia nitrogen concentration was about 50mg/L,the micro aeration 3h(DO was 0.5~0.8mg/L,the stirring 3h(ORP was 54~150 mv),aeration and stirring alternately,and the effluent p H was above 7.5.,half-nitrification was successfully initiated Under the conditions of 20 h HRT and 25?~30?.(6)When the temperature was reduced to 20?,the proliferation of Nitrotoga and the decrease of Nitrosomonas abundance were observed in the reaction system,and the competitive advantage was gradually lost,which led to the destruction of half-nitrification and finally to the whole nitrification.(7)In the process of short-cut nitrification and half-nitrification,it was found that the system has a certain removal rate of total nitrogen.In the absence of organic carbon source in the influent,on the one hand,autotrophic microorganisms produced PS and PN and were used as denitrifying carbon sources by heterotrophic microorganisms to achieve the removal of total nitrogen in the system.On the other hand,aerobic denitrification may exist in the system,on the other hand,there may be aerobic denitrification in the system.Anaerobic ammonia oxidation and other biological denitrification pathways.The results of this study have positive significance for improving the biological nitrogen removal efficiency of wastewater with low total nitrogen and low C/N ratio.Especially for domestic sewage,it was of great significance to realize the semi-nitrification of the system,to reduce the energy consumption of wastewater treatment,to improve the efficiency of nitrogen removal in the system,and to develop a new type of domestic sewage treatment process combination.