Study On Short-cut Nitrification Control And Denitrifying Phosphorus Removal Efficiency In ABR-MBR System

The ABR-MBR system is used to treat domestic sewage.The organic matter in domestic sewage can be effectively removed by Anaerobic baffled reactor（ABR）,and high-quality carbon source can be provided for denitrifying phosphorus removal bacteria.The membrane bioreactor（MBR）is used for nitrification,and the nitrification solution is returned to the denitrifying dephosphorization compartment in ABR for denitrifying dephosphorization.and realize short-cut nitrification and phosphorus removal.Compared with whole-process nitrification,short-cut nitrifying phosphorus removal further saves carbon source and energy requirements.At present,the methods to achieve short-cut nitrification are mostly based on the control of operating conditions,including low DO,high FA,high FNA,high temperature and so on.However,the presence of organic matter and less ammonia nitrogen are not conducive to the growth and reproduction of AOB in the mainstream wastewater,and the temperature of the mainstream wastewater is consistent with the environmental temperature.The low temperature is not conducive to the enrichment of AOB and the inhibition of NOB.Therefore,the application of short-cut nitrification of mainstream wastewater is still under research.In this study,ABR-MBR system was used to treat domestic sewage and realize short-cut nitrification in MBR.The removal of carbon,nitrogen and phosphorus in the reactor and the changes of microbial population were studied,and the following main conclusions were drawn:（1）The porous carriers made of gel was added to the MBR for developing biofilm.DO was maintained in the reactor during 1～4 mg·L-1.The hydraulic retention time（HRT）was shortened to increase the load and control residual ammonia nitrogen concentration in the reactor,the DO/NH₄⁺strategy was adopted to realize shortcut nitrification in the MBR,During stageⅢ,the DO/NH₄⁺ratio was between 0.05～0.2,nitrite accumulation rate（NAR）increased at around 70%,the shortcut-nitrification was achieved.The high concentration of residual ammonia nitrogen in the reactor ensures that DO/NH₄⁺value was in a small range,and the growth rate of AOB in the reactor was higher than that of NOB.At the same time,due to the layered structure of the biofilm（AOB was usually on the outer surface,NOB was on the inner layer）,the dissolved oxygen was used by outer AOB.Oxygen consumption barrier was formed on the surface of the biofilm,which made the internal NOB can use limited dissolved oxygen,so as to achieve the purpose of inhibiting NOB and achieve short-cut nitrification.Under different HRT,the COD concentrations of ABR effluent water were 31.08,44.67 and 34.57 mg·L-1,and the COD removal rate of the system was above 90%.When the HRT of ABR and MBR was 8 h and 3.39 h,respectively,the ABR-MBR system achieves the best phosphorus removal efficiency,and the average phosphorus removal efficiency of the system was 47.25%.（2）When the HRT was constant and increasing the influent concentration,the effects of different influent substrate concentrations on the system were studied,such as the removal effect of carbon,nitrogen and phosphorus.The results showed that with the increase of influent substrate,the amount of organic matter removal and the treatment capacity of compartment A1 were increased,but the COD concentration of ABR effluent was continuously increased,and the average COD concentration of effluent was 34.35,58.13 and 68.28 mg·L-1,respectively.Despite the DO/NH₄⁺-N ratio was low in the MBR,short-cut nitrification was disrupted.The removal efficiency of total nitrogen in MBR increased.Under different operating conditions,the removal rates of total nitrogen and phosphorus were 63.51%,74.87%,78.06%and 26.55%,35.50%,49.35%,respectively.With the increase of influent concentration,the overallremoval efficiency of denitrification and phosphorus in the system also increased.（3）High-throughput sequencing technology was used to analyze the changes of microbial community structure in the denitrifying phosphorus removal compartment and biofilms in the reactor.And the results showed that dominant microbial population in biofilm were Proteobacteria,Chloroflexi,Actinobacteriota,Actinomycetes,Bacteroidota,the abundence of Proteobacteria increased to 44.78%.The abundance of AOB and NOB was small.At the level of genus classification,Acinetobacter was the dominant microorganism,which was responsible for heterotrophic nitrification and phosphorus removal,and its abundance in biofilm were 17.04%and 22%,respectively.In addition,there were many denitrifying bacterias in biofilm,including Denitratisoma and Candidatus＿Brocadia.The abundance of denitrification bacteria increased with the increasing influent concentration in the reactor.The dominant microbial populations in denitrifying phosphorus removal compartment were Proteobacteria,Chloroflexi,and Firmicutes.The dominant microorganisms with denitrifying phosphorus removal were Thauera and Dechloromonas.During the operating,the ratio of DPAOs to the total biomass reached 5.53%.