Study On The Denitrification Performance And Mechanism Of Hydrogen Based Membrane Biofilm Reactor (H2-MBfR) By Controlling Gas Reverse Diffusion

With the development of economy and society,nitrate（NO₃^-）has become the main pollutant in the water environment.The high concentration of NO₃^-in water has posed a serious threat to the ecological environment and human health.Hydrogen-based membrane biofilm reactor（H₂-MBf R）has many advantages in treating NO₃^-pollution,The conventional H₂-MBf R operation mode has the problem that the H₂ mass transfer efficiency decreases under the action of gas back diffusion,which leads to the degradation of NO₃^-removal performance in the reactor.However,so far,no mature regulation strategy has been developed on how to inhibit the gas back diffusion in H₂-MBf R.in this study,two sets of H₂-MBf R were established,equipped with in-situ monitoring and automatic exhaust system.The gas back diffusion in H₂-MBf R was specifically studied,and a new regulation strategy was established to optimize the denitrification performance of the reactor.Its successful application and development has good social,economic and environmental benefits.The main research results are as follows:The results of short-term H₂-MBf R built with 20 cm,40 cm and 60 cm Hollow fiber membrane（HFM）show that the back diffusion is the main reason for the decrease of hydrogen concentration on the surface of HFM.In the short-term H₂-MBf R built with 20cm,40 cm and 60 cm HFM,the H₂concentration at the end of HFM is 399.4μmol/L、318.4μmol/L and 181.9μmol/L respectively.the decrease of H₂ concentration leads to the decrease of electron donors,which affects the thickness of biofilm.The farther the HFM surface is from the gas supply end,the greater the influence of back diffusion and the smaller the H₂partial pressure in the membrane cavity.H₂ supply pressure can inhibit the back diffusion.The greater the supply pressure,the greater the H₂ concentration at the end of HFM,and the less the reactor is affected by the back diffusion.The study found that the increase of H₂ supply pressure did not significantly improve the denitrification performance of the system.After the supply pressure increased from 0.01MPa to 0.05 MPa,the NO₃^-removal flux increased from 0.96 g N/（m²·d）to 1.14 g N/（m²·d）.In addition,the increase of H₂ supply pressure will also cause serious waste of H₂.Among the air supply pressures of 0.01 MPa～0.05 MPa,the air supply pressures most affected by back diffusion are 0.01 MPa and 0.02 MPa.Due to the poor denitrification effect of 0.01MPa gas supply pressure reactor,0.02 MPa is determined as the long-term operation gas supply pressure of the reactor.The periodic law of back diffusion under 0.02 MPa pressure is studied,and the exhaust cycles are determined as 5 min,25 min and 50 min.The reactor was operated with different NO₃^-influent concentration and exhaust cycle.It was found that under the influent concentration of 30 mg N/L,the removal flux of NO₃^-was the best under the exhaust cycle of 5 min and 25 min,reaching 1.37 g N/（m²·d）and 1.35g N/（m²·d）.Due to the excessive waste of H₂ in the exhaust cycle of 5 min,25 min was selected as the exhaust cycle of the reactor for long-term experiment.The long-term experimental results show that the removal flux of NO₃^-is“exhaust+exhaust”>“exhaust+closure”>“closure+closure”under three operation modes;Under the"closed+closed"operation mode,the abundance of denitrifying bacteria（DNB）at the lower level decreased with the distance of HFM from the gas supply end.Under the"exhaust+exhaust"operation mode,the denitrifying bacteria（DNB）at the lower level showed a phenomenon of uniform distribution on HFM.