| In recent years,China’s tungsten smelting industry is booming.A large number of wastewater generated in the smelting process is difficult to treat due to its complex composition,high concentration of inorganic salts and low carbon nitrogen ratio.Therefore,it is of great significance to develop efficient and stable Tungsten Smelting Wastewater Treatment Technology.Membrane bioreactor(MBR)is widely used in wastewater treatment and water resources reuse due to its excellent effluent quality,high biomass concentration and small footprint.However,membrane fouling is still one of the main obstacles to the development and application of MBR.The thesis takes the actual tungsten smelting wastewater as the treatment object,the MBR system with salinity of 3.0%was obtained by using salinity gradient method.During the domestication of activated sludge,the effect of salinity shock on the removal efficiency of COD and ammonia nitrogen,the activity of functional enzymes and the characteristics of functional microbial community were comparatively studied,and the changes of functional microbial flora under the shock of salinity were explored through microbial transcription detection and analysis.At the same time,scanning electron microscopy and energy spectrum analysis(SEM-EDX)technology were used to analyze the difference in membrane surface pollution characteristics.Fourier infrared spectroscopy(FTIR)and three-dimensional fluorescence spectroscopy(3D-EEM)were used to explore membrane pollution characteristics and membrane fouling composition differences.In view of the fact that the design of MBR operating parameters has a greater impact on the treatment efficiency,further studies on the ammonia nitrogen removal efficiency and membrane pollution characteristics of the treatment of tungsten smelting wastewater under different operating parameters of the MBR process have been carried out.Obtained the following research results:(1)Using the integrated MBR as the research platform,starting from the 0%salinity environment,the salt concentration is gradually increased,and finally an MBR system for treating 3.0%salinity tungsten smelting wastewater was established.The research results showed that the instantaneous impact of salinity during the operation of the system has a significant impact on the removal efficiency of COD and ammonia nitrogen,but after long-term acclimatization,the removal efficiency of COD and ammonia nitrogen slowly rises,and after the 3.0%salinity system operates stably,the efficiency more than 86%and 80%respectively,the TN removal effect was stable above 70%,and the simultaneous nitrification and denitrification efficiency(ESND)can still reach about 95%.In addition,salinity significantly inhibited the activity of electron transfer enzyme(ETS),and the activities of nitrifying enzymes(AMO and NXR)were more sensitive to salinity than those of denitrifying enzymes(NIR and NAR).(2)MBR system was mainly composed of Proteobacteria(α,β and γ-Proteobacteria)and Bacteroides.Nitrosomnas halophila has become the dominant species in high salinity environment,especially in 3.0%salinity environment.High salinity envionment has a significant impact on the microbial species composition and functional gene level of the system.At the species level,the richness of microbial flora decreased with the increase of salinity,and the dominant species of microbial flora were different in each operation stage.However,there were a large number of the same basic functional genes in different salinity environments.With the increase of salinity,the relative abundance of functional genes was stable,but the difference of functional genes was significant.(3)With the increase of salinity,the increase of transmembrane pressure difference(TMP)and the thickness of membrane fouling layer increase.The distribution of protein concentration was TB-EPS>LB-EPS>SMP,and the distribution of polysaccharide concentration was LB-EPS>TB-EPS>SMP.The organic composition and content of SMP and EPS changed significantly.The correlation analysis showed that there was a correlation between SMP and TMP,and the correlation of PN was more significant than that of PS,but there was no significant correlation between LB-EPS and TB-EPS.3D-EEM analysis showed that the organic components of LB-EPS were significantly affected by salinity shock,and the changes of organic components in LB-EPS might represent the changes of microbial community.(4)At 3.0%salinity,the operating parameters had significant effects on the formation characteristics of SMP and EPS and membrane fouling rate,and the variation trend of membrane fouling rate with operating parameters was consistent with that of SMP concentration.Considering the membrane fouling and ammonia nitrogen removal efficiency under single factor conditions,response surface analysis was used to optimize the operation parameters and obtain the membrane fouling rate(|KJ|)and ammonia nitrogen removal efficiency(R.E)were obtained.|KJ|=3.77 ×10~12+4.518×10~11 A+3.346×10~11B+8.968×10~11AB-2.403 ×10~11AC-2.228 ×10~11BC+5.267×10~12A~2-7.126×10~11B~2+1.333×10~12C~2+2.273×10~12A~2B+4.202×10~11A~2C+1.819×10~12AB~2 R.E=93.844+19.972A-0.075AB+3.075AC-30.923A~2-3.82C~2-3.983A~2C+0.005AB~2Combined with the actual operation,the optimized parameterization results were HRT=22.30 h,C/N=4.80,DO=1.5～2.0 mg/L. |
