Effects Of Hydrogen Pressure And Influent Velocity On Nitrate Removal In Hydrogen-based Membrane Biofilm Reactor

The problem of groundwater nitrate pollution has become increasingly prominent during recent years,nitrate will be reduced to nitrite under the action of reducing bacteria,which will cause poisoning after consumption.Although the existing physical and chemical technologies have certain effects,there also have problems such as high cost,secondary pollution,and complicated subsequent processing.Hydrogen-based Membrane Biofilm Reactor?MBfR?is a device for organically combining autotrophic biofilm technology with microporous hollow fiber membrane diffusion hydrogen,it can use H₂ to reduce and remove oxidizing pollutants effectively,and has a good development prospect.It has been applied in the removal of oxidative pollutants in water.Hydrogen pressure and influent flow rate are two important regulatory factors in MBfR operation,which not only affect the efficiency and economy of MBfR operation,but also affect the biofilm structure in the reactor.By constructing a small MBfR reactor,the activated sludge in the anaerobic tank of the wastewater treatment plant is selected for domestication,thereby hydrogen-producing bacteria with hydrogen as an electron donor and NO₃^--N as an electron acceptor for removing NO₃^--N in water.By adding essential nutrients for the growth of microorganisms,keep it stable growth in the reactor to complete domestication.Exploring the effect of hydrogen pressure and inlet flow rate on NO₃^--N removal.Using high-throughput sequencing technology to investigate the effects of influent flow rate and hydrogen pressure on longitudinal and lateral microbial communities in MBfR,And determine the dominant strains of their removal efficiency and their corresponding spatial distribution.providing theoretical support for the reactor to maintain stable,long-lasting and efficient operation.The experimental results showed that MBfR had a significant effect on the degradation of NO₃^--N in water.As the hydrogen pressure increases,both the NO₃^--N removal and the degradation rate could be improved,but the continuous increase of hydrogen pressure didn't lead to a linear increase in the removal rate.Considering economic factors,the most suitable hydrogen pressure for the reactor operation is 0.04⁰.06 MPa;In addition,increasing the influent flow rate would reduce the NO₃^--N removal and degradation rate,The optimum flow rate of the reactor is no more than 2 mL/min.Under the changed of hydrogen pressure,High-throughput sequencing analysis showed that the dominant class-level bacteria in the reactor were Gammaproteobacteria?Alphaproteobacteria?Alphaproteobacteria,these three types of bacteria were more sensitive to hydrogen.The dominant genera in the three stages of genus-level were:Stenotrophomonas?Bradyrhizobium and Hydrogenophaga.The results from the analysis of the class level and genus level indicate that when the hydrogen pressure is 0.04⁰.06 Mpa,the dominant species are mainly enriched in the hollow fiber membrane near the inlet.As the hydrogen pressure gradually increases,the enrichment region gradually changes from the proximal end of the inlet to the distal end of the inlet.When the hydrogen pressure is 0.10 MPa,the dominant species are mainly enriched in the hollow fiber at the distal end of the inlet.In the stage of regulating the influent flow rate,the dominant species are mainly enriched in the hollow fiber membrane at the distal end of the inlet at each flow rate.Divided from the horizontal direction of the hollow fiber membrane,the biofilm closer to the hollow fiber membrane is more favorable for the growth of the dominant species.Speraman and CCA were used to analyze the environmental factors of the samples in each stage,and obtained the positive and negative correlation of the samples and bacteria at class-level or genus-level,which could provide data and theoretical support for reactor operation and microbial community research.