Study On Nitrogen Removal Performance And Optimization Of Pilot-scale Three-stage A/O-MBBR Treating Municipal Sewage

With the improvement of economic and urbanization,the country has paid more attention to urban environmental pollution control,but still faces problems such as the shortage of water resources and the pollution of the water environment.At the same time,various local governments have proposed more strict wastewater discharge standards.The traditional wastewater treatment technology represented by the activated sludge method usually suffers from the problems of low denitrification efficiency and the limiting bottlenecks of low temperature treatment.To solve the above problems,a pilot-scale three-stage anoxic/oxic（A/O）moving bed biofilm reactor（MBBR）treating municipal sewage was constructed,and the soluble shemical oxygen demand（SCOD）、NH₄⁺-N and total inorganic nitrogen（TIN）removal performance was investigated.Combined with high-throughput sequencing technology and the changes of biofilm morphology and ability,the composition of system microbial community under different conditions was explored to provide technical support for the construction and optimization of multi-stage A/O-MBBR system stable and efficient nitrogen removal in under cryogenic conditions in a town wastewater treatment plant.The main findings are as follows:（1）When the conditions of system inlet point set in A₁ and A₅ reaction zones、water temperature from 18 to 29℃、treatment water content of 27.2±8.1 m³/d、inlet ratio of1:1 and non dosed carbon source,the average removal efficiency of SCOD、NH₄⁺-N and TIN reached 83.4%、97.2%and 60.3%.When the conditions of system inlet point set in A₁ and A₅ reaction zones、water temperature from 18 to 29℃、treatment water content of 27.4±5.4 m³/d、inlet ratio of 1:1 and 50 mg COD/L carbon source was dosed,the average removal efficiency of SCOD、NH₄⁺-N and TIN reached 83.0%、98.3%and92.5%.When the conditions of system inlet point set in A₂ and A₆ reaction zones、water temperature from 20 to 28℃、treatment water content of 28.8±4.8 m³/d、inlet ratio of 1:1 and non dosed carbon source,the average removal efficiency of SCOD、NH₄⁺-N and TIN reached 76.3%、97.7%and 70.3%.When the conditions of system inlet point set in A₂ and A₆ reaction zones、water temperature from 15 to 21℃、treatment water content of 28.8±4.8 m³/d、inlet ratio of 1:1 and 50 mg COD/L carbon source was dosed,the average removal efficiency of SCOD、NH₄⁺-N and TIN reached74.4%、98.8%and 86.8%.（2）When the conditions of system inlet point set in A₁ and A₅ reaction zones、water temperature from 9 to 15℃、treatment water content of 19.6±2.1 m³/d、inlet ratio of1:1 and 50-90 mg COD/L carbon source was dosed,the average removal efficiency of SCOD、NH₄⁺-N and TIN reached 82.3%、98.9%and 82.3%.When the conditions of system inlet point set in A₂ and A₆ reaction zones、water temperature from 12 to 15℃、treatment water content of 28.8±4.8 m³/d、inlet ratio of 1:1 and 50 mg COD/L carbon source was dosed,the average removal efficiency of SCOD、NH₄⁺-N and TIN reached71.9%、98.2%and 76.0%.（3）The three-stage A/O-MBBR system had good removal effect on SCOD under different temperature conditions,and the first and second A/O-MBBR sub-systems were the main sections of SCOD removal.The reaction zones of O₃、O₄、O₇ and O₈assumed the overall nitrification function of the system.The denitrification performance in anoxic zone of the first and second A/O-MBBR sub-systems was less affected by temperature.（4）At medium-low temperature,when the influent points were set in the A₁ and A₅ reaction zone,due to the difference in biofilm thickness between the aerobic reaction zone of the first and second A/O-MBBR sub-systems,the difference in biofilm nitrification ability between the two sub-systems was formed.Especially for the aerobic reaction zone of the first A/O-MBBR sub-system,the biofilm thickening led to the decrease of nitrification ability.The increase of active autotrophic biomass in aerobic zone may be one of the important reasons for the stable operation of the system under medium-low temperature,and the increase of EPS content in biofilm may be one of the reasons for the thickening of biofilm in aerobic zone under medium-low temperature.（5）Replacing the influent points of the system from the A₁ and A₅ reaction zones to the A₂ and A₆ reaction zones could strengthen the overall nitrification performance of the system and form a reasonable functional partition.When the influent point were set in A₂ and A₆ reaction zones,A₁ and A₅ reaction zones as the pre-anoxic zones,the C/N requirement of denitrification in denitrification function zone could be reduced,and the nitrogen removal efficiency of the system could be effectively improved.At the same time,it was also beneficial to the simultaneous nitrification and denitrification reaction,and the efficient utilization of carbon source in raw water could be realized.（6）Nitrosomonas was the superiority ammonia oxidizing bacteria（AOB）in aerobic reaction zones,Nitrospira、Nitrolancea and Candidatus＿Nitrotoga were the superiority nitrite oxidizing bacteria（NOB）.Compared with condition of the influent points setting in the A₁ and A₅ reaction zones,when the influent points were set in the A₂ and A₆ reaction zones,the NH₄⁺-N load of the system increased by about 20.0%,which was the main reason for the increase in the relative abundance of nitrifying bacteria.（7）The community composition of denitrifying bacteria in anoxic zones was almost the same under different temperature conditions.Sulfuritalea、Denitratisoma、Deluviimonas、Rhodobacter、Lentimicrobium、Flavobacterium、Simplicispira,、Thiothrix and Hydrogenophaga were the superiority denitrifying bacterium.（8）Under medium-low temperature conditions,the increase in the relative abundance of nitrifying bacteria and Flavobacterium might be conducive to the stable operation of the system.At medium-low temperature,when the influent points were set in the A₁and A₅reaction zones,the significant increase in the relative abundance of filamentous bacteria such as Trichococcus and Thiothrix was one of the main reasons for the significant increase in biofilm thickness in the aerobic reaction zone.When the influent points were set in the A₁ and A₅ reaction zones,a large number of anaerobic ammonium oxidizing bacteria were enriched and retained in the system.