Study On The Relationship Between Nitrogen Removal Capacity And Microbial Structure Of Multi-stage A/O-MBBR System

In recent years,China has carried out a lot of work in the prevention and control of urban environmental pollution,but still faces problems such as water shortage,water environment pollution and water ecological damage.Therefore,the effluent quality of urban sewage treatment plants in China is increasingly strict.The traditional urban sewage treatment technology represented by the activated sludge method usually has the bottleneck problem of low-temperature biological nitrification.How to break through the low-temperature restriction bottleneck and realize high-efficiency biological nitrogen removal has become an urgent problem to be solved in the field of sewage treatment.The moving bed biofilm reactor enables nitrifying microorganisms to form enriched growth and maintain strong nitrification capacity under low temperature conditions due to the attached growth of biofilm on the surface of the carrier.Therefore,this study combined a pure membrane MBBR bioreactor with a multi-stage A/O biological nitrogen removal process to construct a two-stage A/O-MBBR pilot-scale system and a three-stage A/O-MBBR pilot system with two-step-feed respectively.On the basis of investigating the treatment capacity of organic matter,ammonia nitrogen and total inorganic nitrogen in the two systems under different working conditions,the removal effect of each reactor the main pollutants was analyzed,the biofilm nitrification capacity of aerobic reactor and biofilm denitrification capacity of anoxic reactor in the two systems were evaluated by static test method,and the changes of biomass,active biomass and functional microorganisms in each reactor were analyzed.The relationship between the macroscopic nitrogen removal ability and the microscopic microbial community structure was studied,which provided some theoretical and technical support for the construction and system optimization of the multi-stage A/O-MBBR system.1.The research results of the two-stage A/O-MBBR system were as follows:（1）The two-stage A/O-MBBR system had good treatment efficiency under different reaction temperatures.Under the conditions of 10～12℃and hydraulic retention time of16.0 h,the influent concentrations of SCOD,NH₄⁺-N and TIN were 157.96±20.34,37.96±1.93 and 39.59±1.86 mg/L,the effluent decreased to 45.29±4.42,2.56±1.67 and14.92±1.20 mg/L,the removal rates were 71.20±3.40,93.26±4.38 and 62.30±2.41%.（2）The change of nitrification capacity of each aerobic reactor in the two-stage A/O-MBBR system was directly related to the autotrophic active biomass and nitrifying microbial community structure,while the change of organic matter removal load had a direct impact on the growth and microbial community structure of nitrifying microorganisms.Under the condition of 10～12℃,the nitrification capacity of biofilm in O₃,O₄and O₅reactors was 0.49±0.04,0.66±0.07 and 1.07±0.09 g NH₄⁺-N/m_·²d,respectively,without considering organic matter loading and non-restrictive ammonia nitrogen matrix.The heterotrophic active biomass of biofilm in each aerobic reactor was2.70±0.05,2.45±0.04 and 2.36±0.03 g COD/m²,and the autotrophic active biomass was0.19±0.01,0.26±0.02 and 0.56±0.03 g COD/m²,respectively.The relative abundance of nitrifying bacteria was 0.14%,0.93%and 1.61%,respectively.（3）The change of denitrification capacity of each anoxic reactor in the two-stage A/O-MBBR system was directly related to the heterotrophic active biomass and denitrifying microbial community structure,while the change of organic load and nitrate nitrogen load had a direct impact on the growth and microbial community structure of denitrifying microorganisms.Under the condition of 10～12℃,the denitrification capacity of biofilm in A₁,A₂,A₆and A₇reactors under unrestricted carbon source and NO_x^--N matrix was 1.10±0.06,0.54±0.06,1.17±0.09 and 0.73±0.07 g NO_x^--N/m_·²d,respectively.The heterotrophic active biomass of biofilm in each anoxic reactor was 2.41±0.04,1.35±0.03,0.68±0.02 and 0.54±0.02 g COD/m²,and the relative abundance of denitrifying bacteria was 32.16%,27.65%,41.28%and 25.00%,respectively.2.The research results of the three-stage A/O-MBBR system with two-step-feed were as follows:（1）The three-stage A/O-MBBR system with two-step-feed had good treatment efficiency under different reaction temperatures.Under the conditions of 10～12℃and hydraulic retention time of 11.7 h,the influent concentrations of SCOD,NH₄⁺-N and TIN were 149.95±21.06,39.43±4.55 and 40.69±4.53 mg/L,the effluent decreased to43.37±4.54,0.31±0.17 and 12.06±1.31 mg/L,the removal rates were 70.74±3.72,99.21±0.42 and 69.88±5.15%,respectively.（2）The change of nitrification capacity of each aerobic reactor in the three-stage A/O-MBBR system with two-step-feed was directly related to the autotrophic active biomass and nitrifying microbial community structure,while the change of organic matter removal load had a direct impact on the growth and microbial community structure of nitrifying microorganisms.Under the condition of 10～12℃,the nitrification capacity of biofilm in O₃,O₄,O₇and O₈reactors was 1.10±0.06,1.23±0.07,1.18±0.04 and 1.29±0.08g NH₄⁺-N/m_·²d,respectively,without considering organic matter loading and non-restrictive ammonia nitrogen matrix.The heterotrophic active biomass of biofilm in each aerobic reactor was 1.08±0.06,0.56±0.04,1.02±0.05 and 0.69±0.04 g COD/m²,and the autotrophic active biomass was 0.24±0.01,0.41±0.03,0.31±0.01 and 0.45±0.03 g COD/m²,respectively.The relative abundance of nitrifying bacteria was 2.37%,5.85%,2.32%and 5.73%,respectively.（3）The change of denitrification capacity of each anoxic reactor in the three-stage A/O-MBBR system with two-step-feed was directly related to the heterotrophic active biomass and denitrifying microbial community structure,while the change of organic load had a direct impact on the growth and microbial community structure of denitrifying microorganisms.Under the condition of 10～12℃,the denitrification capacity of biofilm in A₁,A₂,A₅,A₆and A₉reactors under unrestricted carbon source and NO_x^--N matrix was0.25±0.04,0.73±0.05,0.27±0.03,0.86±0.06 and 1.29±0.08 g NO_x^--N/m_·²d,respectively.The heterotrophic active biomass of biofilm in each anoxic reactor was 0.15±0.02,0.88±0.04,0.17±0.04,0.98±0.03 and 0.77±0.03 g COD/m²,and the relative abundance of denitrifying bacteria was 7.78%,19.71%,6.32%,22.41%and 18.57%,respectively.