The Process Research Based On Inhibition Kinetics:salt-tolerant Partial Denitrification Coupled With Anammox

In the paper,the characteristics of the partial denitrification（PD）and anaerobic ammonia oxidation（Anammox）processes for nitrogen removal in saline wastewater were investigated under the condition of 10g/L salt environment.On the basis,a new process,salt tolerance partial denitrification and anammox（ST-PDA）process was established after salinity adaptation to achieve and maintain high nitrogen removal efficiency in salt environment.To be specific,firstly,the rapid start-up and stable operation characteristics of PD process were studied.Subsequently,the kinetics fitting of PD system salinity inhibition,and the dynamics simulation of substrate and product were investigated in the salt environment.Salinity adaptation experiment of PD and Anammox system were conducted according to the fitting parameters,ST-PDA process was established ultimately.Finally,the change of microbial community structure was analyzed to reveal reaction mechanism from the micro perspective,providing theoretical basis and technical support for the treatment of saline wastewater.Throughout the study,the main research content and innovative achievements of this paper are mainly in the following aspects:（1）Quick start-up of PD system and NO₂^--N accumulation characteristics under different conditionsThe simulated NO₃^--N wastewater was treated with sodium acetate as a single external carbon source,and the residual sludge with denitrification effect was inoculated in the secondary sedimentation tank of a sewage treatment plant.In a sequencing batch bioreactor（SBR）,the rapid start-up of partial denitrification was realized by reasonably controlling the influent NO₃^--N concentration,C/N and reaction time.The NO₂^--N accumulation characteristics under different C/N and NO₃^--N concentrations in influent conditions were studied.The experiment results showed that the PD system could achieve rapid start-up within 25 days without adjusting the influent pH.In addition,PD process could maintain stable and efficient operation under the conditions of influent NO₃^--N concentration of 80mg/L,C/N ratio of 2.8 and reaction time of 1h.The NTR was about 85%,NO₃^--N removal rate was close to 100%and organic matter removal rate was about 70%.Under different influent NO₃^--N concentrations（30 mg/L,60 mg/L,80 mg/L）,the accumulation effect of NO₂^--N in PD process was different.With the increase of NO₃^--N concentration,the time needed for the emergence of the highest NTR was shorter,and the concentration of NO₂^--N in water was higher after the reaction.Under different influent C/N ratio conditions（2.5,2.8,3）,NO₂^--N accumulation effect of PD process did not increase with the increase of organic matter,but showed a trend of first increasing and then decreasing.The operation of PD in a typical cycle illustrated the mechanism of NO₂^--N accumulation.In the operation process,NO₂^--N rapidly converts to NO₂^--N by means of organic matter preventing NO₂^--N transformation.（2）Inhibition kinetics and operation characteristics of PD system under salinity conditionsAfter the PD system could maintain stable operation,the experiment of salinity inhibition kinetics was carried out.Then,the long-term operation characteristics of PD under the salinity condition were investigated with the fitting process and parameter regulation,and the NO₂^--N accumulation in the PD operation process under different sodium chloride（NaCl）conditions was explored.In addition,the Haldane and Aiba models were used to simulate the dynamics of two important factors（substrate:NO₃^--N and product:free nitric acid,FNA）in PD process under salt conditions,respectively,providing theoretical basis for the coupling of ST-PDA process.The experimental results showed that PD process was gradually inhibited with increasing salinity,and would be seriously affected at 36 g/L salinity,but it could promote NO₂^--N accumulation.PD was severely inhibited at 35 g/L salinity during long-term operation in salt environment,and NO₃^--N removal rate was less than 40%,which was basically consistent with the results of salinity inhibition kinetics.Furthermore,the PD system could maintain the optimal performance in the salt environment of 10 g/L,the NTR was maintained above 90%,and the effluent NO₃^--N was maintained at about 3 mg/L.In the salt environment,the appropriate substrate concentration was conducive to PD process.When the substrate concentration（NO₃^--N）was reach 100 mg/L,the NO₂^--N accumulation would be maximumly promoted.It was expected that when the concentration exceeded 200 mg/L,PD process might be affected.FNA could only inhibit the PD process,nevertheless,it could be cancelled out through the self-alkalization effect with PD operation.（3）Establishment of ST-PDA process and analysis of microbial community structureIn order to establish ST-PDA process and realize nitrogen removal in saline wastewater,Anammox was started in a low-salinity environment,and salinity adaptability experiment were carried out on subsequent Anammox system by gradually increasing the salinity gradient,and its long-term operation characteristics under salt environment were investigated.The stable operation of Anammox was achieved at 10 g/L salinity,meanwhile,the PD system also maintained optimal performance at this salinity.Therefore,the ST-PDA process coud be established at 10 g/L salinity.Finally,high-throughput sequencing was used to analyze the changes of microbial community structure in PD and Anammox systems under fluctuating salinity conditions.The results illustrated that Anammox could started and adapted to the salinity at 5 g/L within about 10 days.In 7.5 g/L salt environment,Anammox could adapt to salinity more quickly,with NH4+-N and NO₂^--N removal rates approaching 100%.With the salinity increased to 10 g/L,the Anammox system could not only maintain a high total nitroge n（TN）removal effect,but also the stoichiometric ratio was closest to the theoretical value of 1:1.32:0.3 due to the two-stage salt adaptation.However,the Anammox system could not adapt to the salt environment of 12.5 g/L and 15 g/L.High-throughput sequencing results revealed significant changes in microbial community structure in PD and Anammox systems with salinity variation.Thauera,as a functional bacterium of PD process,increased from 3.3%without salt environment to 15.9%in 10 g/L salinity and 72.3%in 35 g/L salinity respectively.Meanwhile,Candidatus＿Brocadia also became the main functional bacterium of Anammox at 10 g/L salinity environment.