Study On Nitrogen Removal Performance And Modeling Of One-stage Autotrophic Nitrogen Removal Process In EGSB Reactor

One-stage autotrophic nitrogen removal process was an efficient and economical denitrification process,which could complete the process that NH4+-N transformed to N2 by autotrophic bacteria in one reactor.The process had the advantages of less oxygen demand and noadditional carbon source.The Expanded Granular Sludge Blanket(EGSB)reactor was conducive to efficient and stable operation of the reactor,due to the advantages of higher upflow velocity,realizing rapidly granulation and maintaining a large number of active microbial activity in the reactor.In this research,one-stage autotrophic nitrogen removal process in EGSB reactor was applied to investigate the influence factors on nitrogen removal performance and the microbial diversity of EGSB reactor.Based on the theory of death-regeneration in ASM1,the nitrogen removal model of one-stage autotrophic nitrogen removal process in EGSB reactor was established.Simultaneously,the nitrogen removal performance in the reactor and the spatial distribution of microorganisms in the granular sludge was simulated.The main conclusions are as follows:(1)The effect of DO and ammonia concentration on the nitrogen removal performance of one-stage autotrophic nitrogen removal process in EGSB reactor was studied by batch experiment.When the DO in sludge area increased from 0.4 mg/L to 0.8 mg/L,the removal efficiencies of TN gradually decreased,which was 80.2%,75.5% and 67.4% respectively.In order to achieve the dominant position of nitrosation and anaerobic ammonium oxidation in the EGSB reactor,and to maintain efficient and stable nitrogen removal performance,DO in the sludge area was controlled within the proper range.With the increase of inflow ammonia concenteation,the removal efficiencies of TN were essentially unchanged.The ammonia concentration would not affect the nitrogen removal performance,but increase the equilibrium time.The effect of nitrogen loading on the nitrogen removal performance of one-stage autotrophic nitrogen removal process in EGSB reactor was studied by continuous flow experiment.The removal efficiencies of NH4+-N and TN was decreased by reducing the hydraulic retention time(HRT)to enhance the nitrogen loading.Compared with the influent ammonia concentration of 100 mg/L,The EGSB reactor could be elevated higher nitrogen loading when the influent ammonia concentration was 500 mg/L.When the nitrogen loading was 1750 mg/(L·d),nitrogen removal performance of the reactor was optimal,and the average removal efficiencies of NH4+-N,TN and TN removal loading reached 89.2%,73.3% and 1287.8 mg/(L·d).Results of high-throughput sequencing showed that ammonia oxidation bacteria(AOB)and anaerobic ammonium oxidation bacteria(An AOB)were the dominant bacteria in one-stage autotrophic nitrogen removal granular sludge,where the heterotrophic bacteria(HB)and nitrite oxidizing bacteria(NOB)were detected as well.Thereinto,the AOB was Nitrosomonadaceae_uncultured and Nitrosomonas,while the AnAOB were composed Candidatus_Brocadia and Candidatus kudenenia.(2)Based on the theory of death-regeneration in ASM1,the model involved with four kinds microorganisms of AOB,NOB,An AOB and HB was developed with AQUASIM 2.0 software to describe microbial population dynamics and reactor dynomics of one-stage autotrophic nitrogen removal process in EGSB reactor.After the sensitivity analysis and calibration for the model parameters,the simulated results were in good agreement with the measured results.The established model was validated by batch experiments and continuous-flow experiments.The results showed that the nitrogen removal model of EGSB reactor could not only simulate the batch experiments,but also simulate the continuous-flow experiments.(3)The effect of dissolved oxygen,ammonia concentration and hydraulic retention time on the effluent quality was studied by using the nitrogen removal model of EGSB reactor under the stable operation condition of the reactor.The simulation results showed that dissolved oxygen(DO)was closely related to the effluent quality of the reactor and was key factor in determining the distribution of microbial populations in granular sludge.AOB and AnAOB could be reasonably spatial distributed within the particles,when DO was controlled in the appropriate range.Therefor,one-stage autotrophic nitrogen removal process in EGSB reactor played a good synergistic denitrification effect.When the other conditions of the reactor were constant,the different influent ammonia concentration or HRT corresponded to different optimum DO concentration.With the increase of influent ammonia concentration or the reducing HRT,that is,the increase in TN loading,DO concentration would be increased to ensure that AOB and An AOB could be reasonably distributed within the particles,so as to play a good synergistic denitrification effect.The simulation results provided technical guidance for optimizing the operating conditions of one-stage autotrophic nitrogen removal process in EGSB reactor.