Fast Start-Up And Microbial Characteristics Of CANON Technology

The single stage completely autotrophic nitrogen removal over nitrite process developed in late 1990s was recognized as a new simple and quick nitrogen removal process and attracted many researchers'attention because it can save 62.5%of oxygen consumption,almost 100%of organic carbon source and 50%of alkalinity consumption and it has the advantages of short process flow and less sludge production.But its start-up process was so long that becoming one of the main factors restrained its development.In order to overcome this shortcoming,in this thesis a new strategy for rapid starting up CANON process has been studied experimentally in a submerged biological aerated filter with denitrifying bacteria domesticated and enriched by biological membranes.The main factors influencing the process have been analyzed and the characteristics of microorganisms have also been discussed by means of scanning electron microscope and metagenomic high-throughput sequencing of 16SrDNA amplicon in this thesis.The following conclusions have been obtained based on the experiments.?1?Submerged biological aerated filter can be applied for fast starting up CANON process,in which conventional activated sludge from the secondary sedimentation tank of a municipal sewage treatment plant was taken as the seed sludge,the CANON process was successfully started up after the acclimation of sludge microorganisms for 48 days under the experimental conditions of?30±2??,organic carbon free and controlled dissolved oxygen?0.3-0.5mg/L at nitrosation stage;0.1-0.2mg/L at CANON stage?,with the maximum removal ratio of ammonia nitrogen and total nitrogen achieved at 99.9%and 86.5%,respectively.?2?It can be regarded as a sign of CANON process fine start-up that the concentrations of NH₄⁺-N and NO₂^--N decreased synchronously,accompanied by a significant increased in concentration of NO₃^--N and TN removal rate,the combained packing floated because ANAMMOX reacted nitrogen.?3?The optimum technology parameters of CANON behave as:pH 8.0,temperature 32?,and DO from 0.2 to 0.4 mg/L.When pH was inceaseded gradually from 6.5 to 8,the activities of AOB and AnAOB were subsequently increased,so do the system nitrogen removal efficiency.Besides,changes in pH had a greater effect on AnAOB than AOB within this range,so that AnAOB had a relatively wider range of adaptation to pH values and better stability.When the temperature was 32?,CANON performed best in denitrification.A temperature lower or higher than this degree will have an adverse effecton its denitrification.However,the diverse effect on denitrification caused by the temperature was reversible in the range of 28⁴0?.When the DO varied from 0.2 to 0.4,AOB and AnAOB could work properly,being efficient in denitrification mainly by nitrosation and ANAMMOX reaction;when the DO varied from 0.6 to 0.8,AnAOB were inhibited to a certain extent.The larger the value of DO,the greater the effect on nitrogen removal;and compared with the start-up period,the value of DO had less impact on the CANON technology during the stable operation period.?4?Two dominant microbial strains in the system have been found to be Proteobacteria and Planctomycete,played a role in nitrosation and in anammox respectively.The major contributors of nitrogen removal were Nitrosomonas in?-Proteobacteria and Candidatus brocadia in Brocadiae.Both dominant microorganisms had teamed up for biological removal of nitrogen in CANON process.?5?After conventional activated sludge were acclimated by imitated wastewater in SBAF under the experimental conditions of organic carbon free,controlled dissolved oxygen and tempreture,AnAOB were enriched rapidly instead of NOB were eliminated out of the system.From the inoculation period to operating period,abundance of AnAOB continued to increase,from 0.00179%to 30.6%.