Recovery Performance Of Mainstream Partial Nitritation-anammox System

Nitrification-denitrification process has been widely applied in the mainstream nitrogen removal from municipal wastewater,with appearing obvious drawbacks such as large aeration rate,extra carbon source addition,massive sludge yield and high operation cost.Partial nitritation-anammox(PN/A)process,as a new biological nitrogen removal system,has its overwhelming advantages of energy saving,no carbon source addition,low biomass yield and low green-house gas emission,which could show a great potential and a bright prospect for nitrogen removal from municipal wastewater.However,some key puzzles are still hinder the widespread of the PN/A process,including unstable performance especially for the performance decline during long-term continuous operation period.In this study,a typical air lift moving bed bioreactor(ALMBBR)in performance decline state was used for low-ammonia strength synthetic wastewater treatment and recovery characteristics of the overall performance of the mainstream PN/A system were studied.Effects of temperature,aeration rate,influent ammonia nitrogen concentration,free ammonia and free nitrous acid on the recovery of performance and the changes of microbial community structure and functional microorganisms of the mainstream PN/A system during the performance recovery stage were also investigated.The main results are as follows.(1)After deteriorating the performance of ALMBBR reactor,the removal rate of total nitrogen decreased from 80%to 20%.By changing the temperature,aeration rate and influent ammonia nitrogen concentration respectively and maintaining the other system parameters unchanged,the denitrification performance of ALMBBR reactor could be effectively restored after 386 days of continuous operation recovery test.When the influent ammonia nitrogen concentration is 50 mg/L and the water temperature is 29?,the aeration rate is increased from 0.12 L/min to 0.28 L./min,and the total nitrogen removal rate is increased from 27.8%to 57.4%.When the influent ammonia nitrogen concentration is 50 mg/L and the aeration rate is 0.22 L/min,the water temperature is increased from 25? to 35?,and the total nitrogen removal rate is increased from 26.0%to 64.1%.When the water temperature is 29? and the aeration rate is 0.28 L/min,the influent ammonia nitrogen concentration is increased from 50 mg/L to 75 mg/L,and the total nitrogen removal rate is reduced from 58.4%to 35.4%.(2)It takes a relatively long time to recover the performance of ALMBBR reactor in continuous operation.Aeration rate and temperature are the main factors affecting performance recovery,while influent ammonia nitrogen concentration,free ammonia and free nitrite concentration have little effect on performance recovery.(3)After a long-term continuous performance recovery test,the microbial community structure in ALMBBR reactor was significantly changed,and Chloroflexi and Planctomycetes became the dominant groups in the reactor;Nitrosomonas was the dominant ammonia oxidizing bacteria,Acinetobacter and Bacillus were the dominant denitrifying bacteria,and Candidatus Brocadia and Candidates Kuenenia were the dominant anaerobic ammonia-oxidizing bacteria.In conclusion,the ALMBBR reactor in performance decline state for long-term continuous operation can be successfully recovered by changing the key process parameters such as aeration rate and temperature.The microbial community structure and the abundance of dominant functional microorganisms also changed with the PN/A process performance recovery.This study could provide a scientific basis to solve the problem of the mainstream PN/A system in performance decline state during long-term continuous operation period.