Research On Start-up And Stability Control Of Combined Partial Nitritation Anammox System

As an efficient and sustainable wastewater nitrogen removal process,shortcut nitrification anaerobic ammonia oxidation(PN-Anammox)can reduce 50% of oxygen demand and 100% of carbon demand.It has been widely used in wastewater treatment.However,the process still has many problems in practical application,such as long start-up time,difficult stable operation and unclear microbial action mechanism.Therefore,the engineering application of integrated PN-Anammox reactor still faces challenges.In this study,aming at the problems of PN-Anammox process,shortcut nitrification and anammox were started respectively,and the nitrogen removal characteristics of the process were investigated at the same time.Then,the changes of process stability under different C/N ratio and DO concentration were studied.On this basis,the change of sludge morphology and the activity of relevant functional bacteria were explored.Finally,the dynamic changes of microbial community structure and interaction were studied.The main experimental results are as follows:(1)In the start-up stage of PN-Anammox,the control strategy of anammox process was studied.By gradually increasing the influent nitrogen concentration and shortening the hydraulic retention time(HRT),the anammox reactor was started up successfully after 60 days,the maximum nitrogen removal rate(NRR)reached 889.04 mg/(L·d).Secondly,intermittent low-oxygen aeration was used to start partial nitritation,and the partial nitritation was started up successfully after 30 days.Finally,the two kinds of sludge were mixed in a ratio of 1:1.After 30 days of culture,the NRE reached 78% and the NRR reached 634.37 mg/(L·d).(2)In the stability study stage of PN-Anammox,When the C/N ratio was 0.5,the nitrate nitrogen effluent of the system increased significantly,the NOB activity was enhanced,and the NRE decreased to 63.7%.When the addition of organic carbon was stopped,the activity of functional bacteria in the reactor was restored,and the NRE recovered to 83.5%.These showed that the effect of organic carbon on this process was reversible.Then,DO gradient rise experiment was performed.The results showed that when the DO of the system was 0.3 mg/L,the functional bacteria could adapt to the hypoxic environment,and the NRE was 80.7%;When DO increased to1.0mg/L,NRE decreased to 66.3%.The increase of DO significantly affected the performance of PN-Anammox.Moreover,the activity of NOB increased to 3.96 mg N/(h·g VSS),while the activity of anammox decreased to 45.5%,and the extracellular polymeric substances(EPS)on the cell surface increased,resulting in the degradation of system performance.(3)In the DO rising stage,the results of high-throughput sequencing showed that the Proteobacteria,Bacteroidota and Chloroflexi were the dominant phylum in the system.Moreover,Ca.Brocadia and Ca.Kuenenia genus in planctomycetota phylum were detected.The relative abundance of Ca.Brocadia decreased from 1.79% to 0.94%,and the relative abundance of Ca.Kuenenia decreased from 1.42% to 0.11%.In addition,the abundance of Nitrospira increased significantly.The change of these functional bacteria may be the main reason for the degradation of system performance.(4)By analyzing the ecological network among microorganisms,it was found that the interaction relationship among microorganisms was dynamic.It had little effect on the molecular network when DO rose to 0.5 mg/L.The scale and complexity of the network had increased significantly as DO rose to 1.0 mg/L,especially the interaction among Chloroflexi,Proteobacteria and Planctomycetota phylum.Most of the interaction were positive correlation symbiosis.It indicated that heterotrophic bacteria play an important role in PN-Anammox system.Ca.Brocadia always existed as module center in network,indicating that Ca.Brocadia was more adapted to high oxygen environment than Ca.Kuenenia.