Study On The Performance And Microbial Characteristics Of A Partial Denitrification Biofilm Process For The Treatment Of Municipal Domestic Wastewater With Low C/N

Water environment protection is an important issue in the current process of social development.In the field of wastewater denitrification,anaerobic ammonia oxidation（Anammox）as a new autotrophic denitrification process has attracted extensive attention.However,Anammox process takes NO₂^--N as the substrate,while NO₂^--N as the intermediate product will hardly exist in large quantities in water.Therefore,the stable supply of NO₂^--N has become the bottleneck of the development of anammox process.In order to solve the above problems,the partial denitrification（PD）process was used to provide a stable nitrite source for Anammox in this experiment,PD and anammox were coupled into a new denitrification process,PD-Anammox（PDA）.At the same time,in order to solve the problems of difficult enrichment of anammox bacteria and pollution caused by excess sludge,the PDA system（PDA-Bf）was started in the form of cultured biofilm.The process could be a sewage denitrification process with low energy consumption,less excess sludge and good nitrogen removal effect.During the experiment,the long-term operation,optimal regulation and microbial community structure of PDA BF system were also explored,and the start-up process of PDA system with two different fillers was compared.The main research contents of this paper are as follows.（1）In order to explore the suitable start-up conditions of the PD-Bf system and observe the nitrite accumulation characteristics,the experiments were conducted with the remaining sludge from the second sink of the Tuandao wastewater treatment plant as inoculated sludge,and the synthetic wastewater as treated.The experimental process was divided into two phases,initiation and intensification:In the PD biofilm system initiation phase,the inoculated sludge was fed into the SBR reactor,and the PD reactor with membrane sludge mixing was started by running in aerobic/anoxic（O/A）mode followed by anoxic（A）mode;during the performance intensification phase of the PD-Bf system,the SBBR reactor was inoculated with PD biofilm obtained at the previous stage,and the reactor was operated in full anoxic（A）mode,and the PD performance of the system was optimized and regulated.The results showed that in the nitrification and denitrification SBR reactor,the nitrite accumulation performance was strengthened by reducing C/N and shortening the anoxic reaction time,and the PD reactor was successful in 54 days.Further,using pure membrane reactor SBBR and anhydrous sodium acetate as a single carbon source,higher NTR（>70%）was achieved,and the duration of nitrate reduction and nitrite formation was prolonged;By analyzing the changes of microbial community structure during the start-up process of PD BF system,it was found that the proliferation of Flavobacterium and Simplicispira,and the microbial community changed significantly.This phenomenon was confirmed by macrogenome sequencing analysis.（2）In order to enrich anammox bacteria in mature PD-Bf system,PD biofilm was used as inoculated sludge in SBBR reactor,and the substrate composition of synthetic wastewater was changed to start PDA-Bf system.The experimental results were as follows:At the initial stage of system startup,the concentration of NO₂^--N and NH₄⁺-N in the effluent was high,and the decrease of ammonia nitrogen concentration was not obvious,only 0.5～2 mg/L,and there was no Anammox process in the system;After the adjustment of C/N and operation time,the NH₄⁺-N in the system gradually increased to 11.3 mg/L,the effluent concentration of NO₂^--N significantly decreased to 23.71 mg/L,and the Anammox effect appeared in PDA-Bf.On the other hand,the analysis of microbial community structure in the system provided a demonstration for the emergence of Anammox bacteria,the enrichment of functional microorganisms such as Candidatus＿Brocadia in the system can be observed.（3）In order to explore the influence of filler type on the start-up process of PDA,PD floc sludge in long-term operation was inoculated in the reactor to start the PDA system.During the start-up,it was adjusted in a way similar to that of poly system,and the operation mode and substrate concentration of the system were adjusted according to the test contents.During the start-up process,the operation mode and substrate concentration of the system were regulated according to the test content,which is similar to that of Poly system.The test results showed that the ammonia nitrogen removal of SBR reactor was not obvious in the early stage,and the effluent NO₂^--N concentration remains at a high level.However,after the startup and optimization of PDA-Bf system,the ammonia nitrogen removal could reach more than 12 mg/L,and the system had obvious PDA effect.In addition,short-term performance fluctuations occurred in the SBR reactor with PDA performance,which may be related to the properties of K3 filler.The analysis of microbial community structure changes simultaneously during the course of the study,the proliferation of Candidatus＿Brocadia and norank＿f＿＿AKYH767,functional microorganisms related to Anammox,were found.