Effect Of Temperature And Organic Concentration Denitrification Performance Of Anammox Bacteria In SNAD Process

Anaerobic ammonia oxidizing（Anammox）bacteria are anaerobic autotrophic bacteria which don’t need aeration and organic carbon source in the process of denitrification,less sludge production don’t produce greenhouse gases.They have a very broad application prospect to achieve synergistic denitrification and carbon removal with other microorganisms.Therefore,Anammox bacteria are mostly used with other microorganisms to achieve nitrogen removal and carbon removal.For low C/N wastewater,simultaneous nitrification,anaerobic ammonia oxidation and denitrification（SNAD）process can be used.However,Anammox bacteria are easily affected by dissolve doxygen,temperature,organic concentration,free ammonia and free nitrous acid.What’s more,the activity of Anammox bacteria is easily inhibited during operation,resulting in unstable denitrification,so the application of SNAD process needs to be further explored.In this thesis,the low C/N wastewater was used as the research object to explore the effect of temperature and organic matter concentration change on Anammox bacteria and to study the denitrification and carbon removal performance as well as the change of microbial community structure through continuous experiments of Micro-oxygenated ascending flow membrane bioreactor SNAD process and batch experiments of Anammox granular sludge in the process.The main studies are as follows:（1）StageⅠ（1-248 d）The average NH₄⁺-N removal rate was above 90%,TN removal rate was above 85%,and effluent NO₂^--N and NO₃^--N were below 10 mg/L at 35℃in the reactor.Stage II（249-335 d）was cooled down to 30℃,the NH₄⁺-N removal rate was more than 80%,TN removal rate was more than 70%,the effluent NO₂^--N was about 5mg/L,NO₃^--N was about 15 mg/L,and the denitrification performance decreased by 10-15%compared with that at 35℃.Stage III（336-420 d）was cooled down to 25℃,NH₄⁺-N removal rate was 54-73.21%,TN removal rate was 33.87-57.98%,effluent NO₂^--N was about 10 mg/L,NO₃^--N was 20-25 mg/L,compared with 30℃,nitrogen removal performance decreased by 20-30%.（2）At 400 d,the reactor started to deteriorate and sludge expansion occurred,and the TN removal rate decreased to less than 30%.Stages IV and V reduced COD concentration effectively solved the sludge expansion,but the functional bacteria were seriously inhibited and were at adisadvantage in the competition between NOB and filamentous bacteria,NO₂^--N could not be accumulated and the functional bacteria enrichment was difficult.Even if the HRT was extended in stage VI,the average removal rate of NH₄⁺-N was 30-45%,TN removal rate was7-15%,but almost all the converted NH₄⁺-N was converted into NO₃^--N by NOB（40-50 mg/L）,and NO₂^--N accumulation was difficult,and the functional bacteria still could not get enriched and could not recover the reactor performance.（3）Stage I and II COD removal rate 90%,stage III COD removal rate gradually decreased to 62.24%,the effluent COD was up to68 mg/L.Foam appeared in the upper part of the reactor at 350d and gradually increased,and sludge expansion phenomenon appeared,and the reactor performance began to deteriorate at 400d.After decreasing the concentration of organic matter in stageâ…£,the COD removal rate of stageâ…£-VI was more than 90%.（4）Stageâ… ,reactor recovery period sludge concentration increased rapidly and stabilized at about 18 g/L.However,stage III system performance deteriorated and microorganisms started to die in large quantities,sludge was reduced and sludge concentration gradually decreased to 8 g/L.At 400 d sludge expansion was caused by both non-filamentous expansion and filamentous expansion,microorganisms secreted a large amount of PS substances triggered non-filamentous expansion.After lowering the temperature,the aeration was not reduced in time,the amount of DO used by An AOB was reduced,the ability of denitrifying bacteria to use COD was weakened,DO and COD made the originally more filamentous bacteria use their own advantages to proliferate and trigger filamentous expansion.（5）The abundance of 200 d 320 d and 620 d functional bacteria were Nitrosomonas（3.83%0.59%2.38%）,Candidatus＿Jettenia（18.66%5.44%0.98%）,Candidatus＿Brocadia（0%0.024%0%）,denitrosomonas（17.85%18.3%2.92%）,Nitrospira（0.041%0.18%0.13%）and Nitrolancea（0.0034%0%0.0027%）.The temperature was reduced from 35℃to 30℃,the conversion capacity of An AOB decreased,the heterobic denitrifying bacteria were more advantageous in competition with Anammox bacteria for substrate,the abundance of denitrifying bacteria increased,and the abundance of Anammox bacteria decreased.620 d reactor deterioration,the conversion capacity of An AOB increased.But the abundance of NOB increased,the functional bacteria were at adisadvantage in competition with NOB and could not accumulate NO₂^--N was converted to NO₃^--N,and functional bacteria enrichment was difficult.（6）In batch experiments at 35℃25℃and 15℃,Anammox activity increased faster and slower as well as higher activity were 35℃>25℃>15℃.C/N of 0.1 0.3 and 0.5 inhibited Anammox activity compared with no added carbon source,and the higher COD concentration was more severely inhibited.Temperature substrate concentration p H and FA（>20mg/L）affected the activity of Anammox bacteria,leading to adecrease indenitrification capacity.（7）Both COD concentration and denitrifying bacteria competition for NO₂^--N in batch experiments inhibited Anammox bacteria,but the activity could be alleviated with COD degradation and p H adjustment.25℃and 15℃could be effectively improved,however,35℃could not be improved,probably because FA was higher and lowering p H could not be adjusted to a suitable range for Anammox bacteria growth.