Study On The Efficacy And Mechanism Of Ultrasonic Enhanced Canon Process For Treating Low Ammonia Nitrogen Wastewater

Single-stage autotrophic nitrogen removal over nitrite（Canon）is a process in which ammonia oxidizing bacteria（AOB）and Anaerobic ammonium oxidation bacteria（An AOB）are used in the same reactor to convert ammonia to nitrogen.It has great potential in treating wastewater with high ammonia nitrogen and low carbon to nitrogen ratio.However,the currently operating Canon process suffers from slow growth of functional bacteria,easy sludge loss,and unstable operation,resulting in long start-up time,which limits the popularization of the Canon process.Therefore,this study firstly restored the activity of long idle anaerobic ammonia oxidation sludge,and then used it as seed sludge to start the Canon process and treat low ammonia nitrogen（NH₄⁺-N<90 mg/L）wastewater,and then enhanced the Canon process by ultrasound to determine the optimal parameters,and finally studied the long-term treatment effect of the Canon process with and without ultrasound enhancement on low ammonia nitrogen fluctuating influent water by comparison.Finally,the long-term treatment effect of Canon process with and without ultrasound enhancement on low ammonia nitrogen fluctuating influent wastewater was investigated by comparing,in order to promote the application of Canon process to treat low ammonia nitrogen municipal wastewater.The main research contents are as follows.（1）Restoration of anaerobic ammonia sludge that was idle for 240 days due to the epidemic using a UASB reactor,and activity was restored after 7 days of room temperature start-up（18°C）and 6 days of hot start-up（30°C）operation,reaching a stable nitrogen removal state at day 10 of hot start-up,with NH₄⁺-N and NO₂^--N removal rates of 79.26%and 99.22%,respectively,and at the time of stabilization,the dominant anaerobic ammonia oxidation genera were Candidatus Brocadia（27.07%）and Candidatus Kuenenia（11.52%）,respectively.The Canon process was started up using a microaerated upflow sludge bed reactor（MUSB）with a reduced influent NO₂^--N ratio and a DO control strategy of 0.3 mg/L to allow suitable growth conditions for AOB and An AOB,and was successfully started up at day 14 with an average TN removal rate of 79.16%,however,the nitrogen removal capacity was reduced when treating low ammonia wastewater,and the final TN removal rate was 49.54%.（2）The optimal ultrasound parameters were determined by batch test,and the effectiveness of Canon system was enhanced when the ultrasound intensity was 0.1～0.3 W/cm².When the ultrasound intensity was 0.3 W/cm²,the Canon activity reached the maximum value of 40.68mg N/（g VSS）/d after reinforcement,which was 27.48%higher than that of the blank group;when the ultrasound time was 4 min,it reached the maximum value of 41.02 mg N/（g VSS）/d after reinforcement,which was 31.25%higher than that of the blank group,the maximum activity value of 41.02 mg N/（g VSS）/d was reached when the ultrasound time was 4 min,which was 31.25%higher than that of the blank group;when the optimal intensity of 0.3 W/cm² and time of 4 min were used,the fortification maintenance time was 6 days,at which time the activity of 30.35 mg N/（g VSS）/d was close to that of the blank group of 30.86 mg N/（g VSS）/d.（3）Ultrasonic waves can strengthen the treatment effect of the Canon process in treating low ammonia nitrogen fluctuating influent.After four different low ammonia nitrogen concentrations（45 mg/L,65 mg/L,35 mg/L,45 mg/L）fluctuating influent still maintain good nitrogen removal ability,NH₄⁺-N removal rate is 95.49%,TN removal rate is 76.60%,△NO₃^--N/△NH₄⁺-N ratio is close to 0.11,which has good stability.The PN/PS value of the reinforced EPS was reduced by 0.93 compared with the blank group,which promoted the stability of granular sludge and made the sludge float less.Compared with the blank group,the enhanced group showed a 12.02%increase in the abundance of AOB genus Nitrosomonas at the genus level,and a 2.29%decrease in the abundance of An AOB major genus Candidatus Kuenenia due to the coordinated effect between functional groups,while the abundance of nitrite oxidizing bacteria genus Nitrospira decreased by 0.53%.