Study On The Technology Optimization Of Moving Bed Biofilm Reactor(MBBR) With Different Reaction Modes

With the national emphasis on water environmental quality,the discharge standard of pollutants for municipal wastewater treatment plant is getting stricter,many mucicipal wastewater treatment plants are upgrading or rebuilding.However,there are still some problems in the operating,such as low nitrogen and phosphorus removal capacity and efficiency,unstable process,high operating cost,etc.Especially the problem of poor nitrification performance in winter under low temperature conditions in northern China has not been solved well.Therefore,how to optimize existing processes and explore a new technology for efficient nitrogen and phosphorus removal with low carbon source have become an urgent need in the wastewater treatment industry.Moving bed biofilm reactor?MBBR?is a highly efficient new biofilm treatment method that has emerged in recent years and has been widely implemented in the field of biological nitrogen removal in sewage.The nitrogen removal performance of MBBR is affected by process operating conditions?such as temperature,dissolved oxygen?DO?,organic load,filler filling rate,etc.?.Therefore,how to optimize these process operating conditions to enhance the nitrogen removal performance and solve the biological nitrogen removal technical bottleneck have become a hot spot for researchers universally.In this study,the laboratory-scale MBBR system was used as the research subject.By investigating the influence of different parameters and operation modes on the nitrogen removal rate in MBBR system,the optimal MBBR control mode was achieved to provide theoretical and technical support for full-scale biofilm nitrogen removal process.The main findings are as followed:?1?For the biofilm microorganisms of MBBR system,the reaction temperature is an important factor affecting the nitrification and denitrification functions,and the dissolved oxygen level is a regulable factor affecting the nitrification function of biofilm microorganisms.When the system temperature is 22 ^oC and DO is 5-8 mg O₂/L,the specific nitrification load of the biofilm can reach more than 1.60 g NH₄⁺-N/?m²·d?,and the specific denitrification load can reach 2.84 g NO₃^--N/?m²·d?,the removal rate of NH₄⁺-N and TN in MBBR system reached 98.7%and 85.7%,respectively.From the perspective of biofilm microbial structure of MBBR system,the variations of dissolved oxygen level mainly lead to the change of the amount and structure ratio of nitrifying functional microorganisms,especially for the growth of heterotrophic nitrifying bacteria.The effect of temperature on denitrifying bacteria is mainly reflected on the changes in community structure.?2?The artificial strengthening:adding Fe³⁺can significantly improve the biofilm microbial nitrification performance of MBBR system and solve the problem of low temperature nitrification.The average removal rate of NH₄⁺-N and COD by artificially enhanced MBBR system can be as high as 97%and 82.5%,respectively.The maximal specific nitrification ratio and average specific nitrification rate of biofilms in artificially enhanced MBBR system at 2-18^oC were 2.74 g NH₄⁺-N/?m²·d?and 1.46 g NH₄⁺-N/?m²·d?,94.3%,respectively,60.0%higher than conventional MBBR systems.At low temperature of 3-8 ^oC,the specific nitrification load of the system can reach 1.23 g NH₄⁺-N/?m²·d?.?3?For the artificially enhanced AO mode MBBR system,the average TN removal rate in the system is 71.9%,the average NH₄⁺-N removal rate is 95.7%,the average COD removal rate is 88.9%,and the average PO₄^3--P removal rate is 45.5%.Artificially enhanced A-O mode MBBR system COD removal load changes also affect the system nitrification effect.At 30^oC,when the system organic load is 3.86 g COD/?m²·d?,the average specific nitrification rate and maximum specific nitrification rate of the system are 2.30 g NH₄⁺-N/?m²·d?and 5.18 g NH₄⁺-N/?m²·d?,respectively.The average specific denitrification rate and maximum specific denitrification rate of the system were 3.47 g NO₃^--N/?m²·d?and 5.11 g NO₃^--N/?m²·d?,respectively.?4?For the artificially enhanced SBR mode MBBR system,the average TN removal rate of the system is 66.9%,the average NH₄⁺-N removal rate is 85.2%,the average COD removal rate is 88.9%,and the average PO₄^3--P removal rate is 82.6%.Artificially enhanced SBR mode MBBR system COD removal load changes also affect the system nitrification performance.At 26°C,when the system organic load is2.06 g COD/?m²·d?,the average specific nitrification rate and maximum specific nitrification rate of the system are 1.87 g NH₄⁺-N/?m²·d?and 3.18 g NH₄⁺-N/?m²·d?,respectively.At 30°C,when C/N is 3.54,The average specific denitrification rate and maximum specific denitrification rate of the system were 3.29 g NO₃^--N/?m²·d?and5.17 g NO₃^--N/?m²·d?,respectively.