Rapid Start-up Of An Gas-lift Nitrogen Internal Circulation ANAMMOX Reactor And Analysis Of Nitrogen Removal Performance Based On Sludge Granule Size

Anaerobic ammonia oxidation(ANAMMOX)process has become one of the most promising technologies in the field of biological denitrification because of its significant advantages such as low aeration,carbon-free feed,low sludge yield and low greenhouse gas emissions.The slow multiplication rate of anammox bacteria(AnAOB)and the instability of the system hinder the sustainable development of anammox,and the study of the rapid start-up of anammox system and the granulation of anammox sludge are conducive to the actual promotion of anammox.In this paper,the rapid start-up mode and nitrogen removal performance of a novel gas-lift anammox reactor with a nitrogen gas circulation were evaluated,the structural characteristics of microbial communities in the stable operating stage reactor were analyzed and the properties of anammox sludge with different particle size were compared from the perspectives of sludge activity,and extracellular polymeric substance(EPS),so as to provide recommendations for the rapid start-up of anammox process and the evaluation and optimization of particle size of anammox granule sludge.The specific results are as follows.Evaluation of reactor performance:(1)In view of the traditional up-flow anaerobic sludge bed(UASB)reactor prone to produce dead zones and other issues,in this experiment,a novel gas-lift anammox reactor with a nitrogen gas circulation was used to achieve a good mixing state inside the reactor,During start-up phase,the dissolved oxygen loading of inlet water was an important control factor for the start-up of the anammox process,this study reduced the effect of dissolved oxygen loading on AnAOB enrichment by increasing HRT,and the inlet matrix concentration was gradually increased to increase the nitrogen loading rate(NLR).Finally,the anammox system was successfully started after 35d.During the stabilization period,the average removal rate of NH4+-N and NO2-N was 86.27%and 90.29%,respectively.The average removal rate of total nitrogen(TN)was 81.27%,the nitrogen loading rate(NLR)reached 2.6 kg/(m3·d)and the nitrogen removal rate(NRR)reached 2.12 kg/(m3·d),respectively.Finally,the novel gas-lift nitrogen internal circulation anammox reactor achieved efficient nitrogen removal function.(2)High-throughput sequencing results showed that in the 5 different particle size samples in this experiment,anammox bacteria(AnAOB)achieved maximum concentration in AMX2(0.5?1.0mm),and the dominant strains of AnAOB were Candidatus Brocadia and Candidatus Kunia,and it was found that Denitratomais and Candidus Brocadia had similar trends in abundance with the change of granule size.There might be some complex synergy mechanism between Denitratisoma and Candidatus Brocadia in the gas-lift nitrogen internal circulation anammox reactor.Evaluation of granule size:(1)The activity test and EPS test results showed that the specific anammox activity(SAA)of granule sludge was significantly higher than that of floc sludge,And the SAA of AMX2(0.5?1.0mm)was the highest at 345mgNH4+-N/(g·VSS·d),which gradually decreased as the particle size continued to increase.Due to the effect of dissolved oxygen(DO)loading in the influent,there were still a small amount of AOB and NOB in the floc sludge,and almost no ammonium oxidizing bacteria(AOB)and nitrite oxidizing bacteria(NOB)in the granules;(2)The content of LB-EPS in AMX4(1.5?2mm)was low,it was assumed that the granule stability of AMX4 might be higher than other granules.In addition to AMX5(>2.0mm),SAA was positively correlated with S-EPS,LB-EPS,TB-EPS,total EPS,the interaction between SAA and EPS of anammox sludge was visible,when the sludge granule size was small,the internal transfer resistance was small,and the higher SAA promoted synthesis of EPS,and the synthesis capacity of EPS would also decrease with the reduction of SAA;When the granule size was large and the mass transfer resistance increased,EPS would hinder the continued improvement of SAA,SVI value of anammox sludge was negatively correlated with the ratio of PN/PS,i.e.the higher the value of PN/PS,the better the settling performance.In the range of 0?2mm granule size,the relationship between SVI and total EPS was also significantly negative correlated,and the higher the total EPS content,the better the settling performance.(3)In summary,the anammox granule sludge of 0.5?2.0mm in size has a relatively high SAA and AnAOB abundance,better settling performance and granule stability,so it is important for the stable operation of anammox system to cultivate the particle size of anammox sludge in the range of 0.5?2.0mm.