Effect Of Hydroxylamine On Nitrogen Removal And Microbial Community Structure Of Completely Autotrophic Nitrogen Removal Over Nitrite Process

The effective suppression of the activity of nitrite oxidizing bacteria（NOB）was the key to the stable operation of the completely autotrophic nitrogen removal over nitrite（CANON）process.It was found that hydroxylamine（NH2OH）,as the intermediate product of nitrification and anaerobic oxidation of ammonium（ANAMMOX）process,had certain toxicity to ammonium oxidizing bacteria（AOB）and NOB.Adding a certain amount of NH2OH to CANON reactor can effectively promote the reaction rate of shortcut nitrification and ANAMMOX,and improve the nitrogen removal performance of CANON reactor.The purpose of this paper was to how to quickly start CANON process and improve the nitrogen removal rate of CANON process,as well as the methods of shortcut nitrification and rapid start-up of CANON process.The effects of adding time and amount of hydroxylamine on nitrogen removal performance and microbial community structure of the reactor under low ammonia concentration,and the effects of NH2OH on the recovery performance of the reactor by high concentration of nitrite and room temperature shock under high ammonia concentration.The main conclusions were as follows:（1）First,the ordinary activated sludge was used as inoculated sludge to keep the water temperature at 30±2℃and p H at 9.3±0.2,by increasing the influent ammonia concentration and gradually shortening hydraulic retention time（HRT）to start shortcut nitrification.After 24days,the ammonia removal rate and the nitrite accumulation rate were all stable at over 90%.It showed that high p H and high ammonia concentration made the free ammonia（FA）concentration was higher in the reactor,which was beneficial for the enrichment of AOB.Subsequently,the shortcut nitrifying sludge was transferred to ANAMMOX sequencing batch biofilm reactor（SBBR）,which was beneficial for the growth of AOB on the outside of anaerobic ammonium oxidizing bacteria（AAOB）,soon,AOB and AAOB grew together.After only running for 18d,the CANON reactor was successfully started,and the ammonia removal rate was stable at 99%,the total nitrogen removal rate reached 83.63%.（2）The operation of CANON process was unstable at the low ammonia concentration,which was mainly affected by the activity of NOB.Adding NH2OH can effectively inhibit the activity of NOB,the higher the NH2OH concentration was,the more obvious the inhibitory effect on NOB.Adding a certain amount of NH2OH can effectively promote the reaction activity of AOB and AAOB,when the concentration was higher,it will also inhibit the activity of AOB,but the reaction activity of AAOB was increased because AAOB can use NH2OH to react.Based on the results of this experiment,it can be considered to add 5 mg·L^-1 NH2OH periodically for 7 days to enhance the stability of nitrogen removal performance of CANON process in the actual operation process of CANON-SBBR.（3）Compared with the low ammonia concentration,higher FA concentration made CANON reactor run stably under high ammonia concentration.Under the high ammonia concentration,the growth rate of functional bacteria was faster,which made the reaction rate increase obviously under the same substrate concentration.The raction activity of AOB and AAOB was similar to the low ammonia concentration,had high activity,but the activity of NOB was at a low level.After the reactor was shocked by 133 mg·L^-1 nitrite,the activity of functional bacteria was seriously affected,adding 5 mg·L^-1 NH2OH can promote the recovery of the reactor.Compared with that before the room temperature shock,the activity of AAOB and AOB decreased by 18.93%and 11.56%respectively on the day of room temperature shock.The microorganism had hysteresis to the change of temperature,and then on the first day after the temperature returned to normal,the activity of AAOB and AOB decreased by 51.19%and46.67%respectively.There was no nitrite accumulation during the reaction process,the nitrogen removal performance of the reactor recovered rapidly after adding NH2OH.（4）16r RNA high-throughput sequencing technology was used to analyze the microbial community structure in CANON system under different conditions.The results showed the total amount and diversity of bacteria in the reactor were lower under the low ammonia concentration.Compared with the low ammonia concentration,the total amount of bacteria in the reactor was higher and the diversity of bacteria was more abundant under the high ammonia concentration.Adding 5 mg·L^-1 NH2OH compared with 10 mg·L^-1,the latter had a slightly higher the number of bacteria,and the former had a slightly richer the diversity of bacteria.At the phylum level,proteobacteria and planctomycotes were the main denitrifying bacteria,with the highest abundance of 31.65%and 31.32%respectively.At the genus level,the dominant genus of ANAMMOX were Candidatus Jettenia and Candidatus Brocadia,the dominant genus of shortcut nitrification was Nitrosomonas,and the dominant genus of nitrification was Nitrospira.