Start Up And Operation Performance Enhancement Mechanisms Under Different Iron Conditons In Completely Autotrophic Nitrogen Removal Over Nitrite (CANON) Processes

Anammox bacteria were widely exist in freshwater and Marine.Compared with the traditional nitrification and denitrification process,completely autotrophic nitrogen removal over nitrite?CANON?based on ammonia oxidizing bacteria?AOB?and Anammox bacteria could save about 60%of oxygen consumption without adding any exogenous organic carbon.In addition,this process also has the advantages in infrastructure,operation costs,and energy consumption and recovery.However,the disadvantages including longer start-up period,lower biomass yield,lower nitrogen removal loading,and easily restricted by operation conditions limited its industrial application.In this experiment,Anammox mixculture was enriched by controlling HRT,adjusting the total nitrogen loading and adding Fe???and Fe???in an upflow activated sludge bed reactor.The effects of Fe???and Fe???on the start-up and operation performance of the CANON process were investigated.The main objectives were to solve the imbalance problems of function bacteria and granulation difficulty in CANON process.Then the performance enhancement strategy based on the regulation of iron was proposed,which was advantage to the efficient operation and industrial application of CANON system.The main research contents and results are presented as follows:?1?For the enrichment culture of Anammox bacteria source for the CANON process,a laboratory scale UASB reactor was constructed.The Anammox process was started up by seeding the activated sludge from a secondary sedimentation tank in a municipal sewage treatment plant.The performance of Anammox was enhanced by ajust nitrogen loading rate regulation and adding exogenous Fe???addition,thus the anammox granule sludge was enriched and cultured.Experimental results showed that loading rate regulation?including substrates and hydraulic loading rate?,the TNRE reached 83.34±2.96%in anammox system with the stoichiometric ratios REANE and REANA of 1.10±0.08 and 0.28±0.05,respectively.These values were close to the theoretical values of 1.32 and 0.26,respectively.Obviously,Anammox reaction became the dominant reaction of the system.The Stover-Kincannon model and the second-order dynamics model have a high correlation coefficient for the fitting results of the Anammox performance using the quasi-steady state data,which is suitable for the describing the operation performance of Anammox system.According to the predicted results of the Stover-Kincannon model,TNRR_max was 25.4kg m^-3 d^-1,which was far higher than the experimental value of 14.4kg m^-3 d^-1,indicating a good denitration potential in Anammox systems.After long-term operation Anammox granulation is obvious and 58.3%of the total sludge had a granular diameter of greater than 2.00mm.The PN/PS ratio in EPS was still lower than the reported values in published literature,suggesting a satisfactory sludge sedimentation performance.With the increase in sludge granular,the iron content detected in EPS gradually decreased,With the increase of sludge particle size,the iron content detected in EPS gradually decreased,but increased in sludge.This result showed that iron is easy to be accumulated in Anammox bacteria under iron-rich environment,which improved the nitrogen removal performance in Anammox process.?2?In order to enhance the performance of CANON process with activated sludge as inoculated sludge,three upflow activated sludge bed reactors were constructed and parallelly operated.The effect of different valences of iron on the start-up and operation performance of the CANON process was studied with synthetic wastewater as influent,and the bacterial structure evolution characteristics were alao investigated.Experimental results showed that the presence of low concentrations of Fe???and Fe???could promote the nitrogen removal capacity in CANON system,and enhance the production of EPS.The optimal concentrations of Fe???and Fe???in this study were 5.3mg L^-1.Further increasing in iron concentration did not significantly increase the denitrification performance of the CANON system.Fe???and Fe???of 8.3mg L^-1had the same nitrogen removal effect as Fe???of 2.3 mg L^-1?R₁,R₂ and R₃ in stage ??.The presence of 5.3mg L^-1 Fe???and Fe???contributed to the significant increase of PN and PS content in EPS.Due to the adsorption of iron by EPS and sludge bacteria,the remaining Fe???and Fe???in the sludge still had a promoting effect on the operation performance in a long operation period after removing Fe???and Fe???in influent.Even substrate concentration was increased and substrate inhibition occured,the nitrogen removal performance still improved after long-term operation.Nitrosomonas and Ferruginibacter were detected as the dominant bacteria by high-throughput sequencing analysis.However,Anammox bacteria was not directly detected in each reactor due to insufficient sequencing depth,The lackness of Anammox bacteria was the key limiting factor that leads to the long-term failure to further improve the nitrogen removal performance in CANON systems.?3?To further enhance the operational performance of the CANON process,efficient Anammox sludge was inoculated into the CANON process,the effects of different iron ions on CANON performance,functional bacteria activity changes,and sludge characteristics were explored.Experimental results showed that the autotrophic nitrogen removal ability of the system was enhanced after the Anammox granular sludge was added into the reactor.However,the changes of DO and other conditions affected the operation performance.Low concentration of Fe???and Fe???(2.3mg L^-1)promoted the autotrophic nitrogen removal ability of the reactor,and the effects of Fe???was superior to that of Fe???.High concentration of Fe???and Fe???(8.3mg L^-1)inhibited the autotrophic nitrogen removal ability of the reactor,and Fe???showed stronger inhibitory effects than Fe???.Further increasing the Fe???concentration inhibited the AOB activity,while Fe???inhibited both AOB and NOB activity.Thus CANON reaction rate and Anammox rate were severely inhibited,leading to a decreasing in the nitrogen removal performance of reactors R₁ and R₂.High-throughput sequencing analysis results indicated that Proteobacteria,Chloroflexi and Planctomycetes were always dominant in each reactor.Candidatus Jettenia and Candidatus Brocadia were the dominant species of Anammox and Nitrosomonas were the dominant species of AOB.The presence of Fe???inhibited the growth of AOB and made the distribution of various Anammox bacteria more even.The presence of Fe???reduces microbial diversity.KEGG analysis found that the gene abundance in the metabolic process did not change significantly with the increase of influent Fe???or Fe???concentration,indicating that the adaption of microorganisms to the change of influent Fe???or Fe???concentration through function succession.