Study On The Performance Of Anaerobic/Aerobic/Anoxic SNiDPR-PED System For Synchronous Treatment Of Municipal Wastewater And Nitrate Sewage

In recent years,the pollution problem caused by excessive nitrogen and phosphorus in water has become more and more serious.Simultaneously,the country has strengthened the control of wastewater discharge standards.Therefore,it is of great significance to develop a stable,economical and efficient simultaneous nitrogen and phosphorus removal process.Based on sequencing batch reactor?SBR?,using anaerobic/aerobic/anoxic operation mode,this article proposed the simultaneous nitritation,denitrification and phosphorus removal-post endogenous denitrification?SNiDPR-PED?system,which is the combination of simultaneous nitritation,denitrification?SNiD?,enhanced biological phosphorus removal?EBPR?and post endogenous denitrification?PED?process in a single SBR.The optimal operation of the system is realized by adjusting the operation parameters and analyzing the influencing factors.At the same time,the relationship between the simultaneous nitrogen and phosphorus removal performance and the functional bacteria was analyzed by using high throughput sequencing technology.In addition,by strengthening the denitrification performance of the system,the feasibility of treating low carbon nitrogen ratio?C/N?municipal sewage and nitrate wastewater by the system was proved,providing theoretical basis and technical guidance for the promotion and application of the system and the research on deep nutrient removal technology of sewage.The main research contents and achievements of this paper were as follows:?1?The optimized operation of SNiDPR-PED system was realized.Firstly,the residual sludge in the anaerobic/aerobic operation SBR reactor was used as the inoculation sludge and the low C/N?about 4.46?municipal sewage was taken as the treatment object,and added post anoxic phase to realize the coupling of EBPR,SNiD and PED process.Then,the optimal operation of SNiDPR-PED system was realized by regulating aeration rate and anoxic time.The experimental results showed that when the aeration rate was decreased from 1.0 L/min to 0.8 L/min and anoxic duration was 150 min,the effluent PO₄^3--P concentration decreased from 0.06 mg/L to 0,the effluent NH₄⁺-N,NO₂^--N and NO₃^--N concentrations gradually decreased from 0.18,18.79 and 0.08 mg/L to 0,16.46 and 0.05mg/L,respectively,and the TN removal efficiency increased from 72.69%to 77.97%.With the reduction of aeration rate,the SNiD phenomenon became obvious,and the SNiD rate increased from 19.18%to 31.20%.Lately,when the anoxic duration was extended from150 min to 390 min,the effluent PO₄^3--P,NH₄⁺-N and NO₃^--N concentrations stabilized at about 0,0 and 0.03 mg/L,respectively,the effluent NO₂^--N concentration was as low as3.06 mg/L,the SNiD rate was about 32.21%.The TN removal efficiency was as high as99.42%,indicating that system has highly efficient nutrient removal performance,which can be used for deep treatment of municipal wastewater.?2?The characteristics of nitrogen and phosphorus removal performance of SNiDPR-PED system under different C/N conditions and the changes of bacterial flora were investigated.In order to know the influence of influent C/N on SNiDPR-PED system under the condition of low C/N municipal wastewater,the effects of different influent C/N?5,4,3,2?1,respectively?on nitrogen and phosphorus removal performance and functional bacteria of the system were studied by regulating influent COD concentration.The experimental results showed that reducing influent C/N properly had little effect on the nitrogen and phosphorus removal performance of SNiDPR-PED system.When influent C/N was 5 and 4,the TN and PO4^3--P removal efficiencys were maintained at a high level,which were 97.13%,100%and 96.01%and 98.75%,respectively.However,when influent C/N dropped to 2?1,the nitrogen and phosphorus removal performance of the system was poor,TN removal efficiency of the system dropped to 71.10%,PO4^3--P removal efficiency was as low as 7.61%.Meanwhile,with the decrease of influent COD load,the simultaneous nitritation and denitrification process of this system was greatly affected,and the end of aerobic NO2^--N and NO3^--N concentrations gradually increased,and the SNiD rate decreased from 36.63%to 8.57%.Besides,high-throughput sequencing results showed that with the decrease of influent C/N,the microbial species richness and biodiversity in the system gradually decreased,and the nitrite oxidizing bacteria?NOB,0.2%?1.7%?,phosphorus accumulating bacteria?PAOs,11.4%?2.9%?and glycogen accumulating organism?GAOs,8.0%?3.4%?in the system changed,which further explained the deterioration of nitrogen and phosphorus removal performance of the system.?3?The feasibility of SNiDPR-PED system for synchronous treatment of municipal wastewater and nitrate wastewater was studied.According to the above test results,using SBR reactor fed with low C/N?about 3.8?municipal and nitrate wastewater?about 100 mg/L?to realize the synchronous treatment of municipal and high-nitrate wastewaters by SNiDPR-PED system.First,the aeration rate was reduced from 1.0 L/min to 0.6 L/min.Then,the aerobic time was extended from 150 min to 180 min and the anoxic time was extended from 180 min to 420 min,the nitrogen removal performance of SNiD and PED was gradually enhanced.Since,nitrate wastewater was added to the anoxic stage to study the feasibility of synchronous treatment of municipal and high-nitrate wastewater.The experimental results showed that without external carbon source,the system could realize the synchronous treatment of municipal and high-nitrate wastewaters by utilizing the limited carbon source in municipal sewage.High TN and PO₄^3--P removals?93.10%and 99.9%,respectively?were reached,of which PO₄^3--P was removed via SNiDPR,the TN removal was mainly achieved by PED in anoxic stage,and the contribution of PED to N removal was up to 60.7%.High-throughput sequencing analysis demonstrated that Nitrospira?0.1-0.4%?was outcompeted by Nitrosomonas?4.7-3.3%?,which ensured stable nitritation in aerobic stage and the NAR was about 99.62%,and the carbon source requirements for SNiD and PED in the system were significantly reduced while the aeration was saved.Dechloromonas?8.5-5.6%?and Candidatus Competibacter?9.1-11.3%?with high relative abundance,which were the dominant functional bacteria to promote anaerobic organic carbons utilization and realize internal carbon source storage.Consequently,the effects of nitrogen and phosphorus removal was guaranteed in the system.