| With the rapid development of China’s social economy and the acceleration of urbanization,the problems of water environment pollution and water resource shortage are becoming increasingly prominent.Membrane bioreactor,as an efficient wastewater treatment technology that combines biological treatment technology and membrane separation technology,has been increasingly widely used in the field of wastewater treatment and resource utilization in recent years.Ceramic membrane is especially suitable for MBR wastewater treatment system due to its advantages such as good chemical stability,high mechanical strength,and long service life.In recent years,its application proportion in MBR system is also increasing;Although compared with organic membrane,Ceramic membrane has many advantages,membrane pollution of Ceramic membrane MBR system is still unavoidable.Ultrasound,as a new alternative technology for membrane fouling control,has advantages over traditional membrane fouling control methods such as simple operation,avoidance of secondary pollution from chemical cleaning,and online control of membrane fouling;The high strength and good stability of Ceramic membrane make the ultrasonic membrane pollution control technology more applicable.Therefore,in view of the difficulties in realizing online membrane pollution control of Ceramic membrane MBR,this topic has constructed an ultrasonic Ceramic membrane MBR system.On the basis of ensuring the sewage treatment effect,the ultrasonic parameters that can optimize the membrane pollution control effect have been tested and screened,and the mechanism of ultrasonic wave to achieve online membrane pollution control has been preliminarily explored,and then the ultrasonic Ceramic membrane MBR system has been further optimized,Thus providing theoretical basis and technical support for the practical application of ultrasonic technology in the field of membrane pollution control.The Ceramic membrane MBR system was constructed,and the water treatment characteristics of Ceramic membrane itself were tested.The results showed that the pure water flux of Ceramic membrane increased linearly with the increase of pressure,and the critical flux of Ceramic membrane in this MBR system was 45 L/（m2·h）.Ultrasonic parameters of Ceramic membrane MBR system were optimized experimentally.A single factor impact experiment was conducted on ultrasound power and ultrasound time,and the optimal parameter ranges for ultrasound power and ultrasound time were selected as 100-300W and 3-7min,respectively;On this basis,a four factor three level orthogonal experiment was constructed with ultrasound power,frequency,time,distance between sound source and membrane surface as influencing factors,and transmembrane pressure difference（TMP）as response value,and the results were analyzed for range;The orthogonal experimental results indicate that the optimal operating parameters for ultrasound under this experimental condition are ultrasound frequency of 28KHz,power is 200w,time of7min,and distance between sound source and film surface of 8cm;Under this condition,the ultrasonic Ceramic membrane MBR system was operated,and the MBR without ultrasonic Ceramic membrane was used as the control group to monitor the changes of the effluent quality and TMP of the two systems during stable operation.The results showed that the average removal rates of COD,ammonia nitrogen,total phosphorus and turbidity in the effluent of the ultrasonic group were 97.4%,95.9%,37.4%and 90.6%,which were similar to the control group,but the total nitrogen removal rate was 10.3%lower than the control group;Ultrasound has a significant effect on membrane pollution control.The growth rate of TMP of Ceramic membrane in the ultrasound group is significantly slower than that in the control group,and the time to reach the pollution end point is 2.4 times that in the control group.The effects of ultrasound on sludge mixture,biological pollution,hydrophilicity of Ceramic membrane and distribution of pollution resistance during system operation were investigated.It was found that compared to the control group,ultrasound reduced the sludge concentration in MBR by 7.5%,which is beneficial for membrane fouling inhibition;The average particle size of sludge in the ultrasound group was about 30%lower than that in the control group;Although the sludge activity of the two systems fluctuated,it remained stable at 6～9 mg O2/g MLSS·h overall,indicating that ultrasound did not disrupt the activity of microorganisms in the system;The EPS of the ultrasound group was slightly higher than that of the control group,and its SMP content was relatively stable.The average protein and polysaccharide concentrations were 27.6%and 18.3%lower than those of the control group,respectively.The results of three-dimensional fluorescence spectrum showed that the main organic substances in the supernatant and effluent of the two systems were fulvic acid and humic acid,and the Ceramic membrane in the ultrasound group had partial retention effect on organic components;The results of contact angle measurement showed that the application of ultrasound slowed down the decrease of the hydrophilicity of Ceramic membrane;The SEM-EDS comparative analysis of the two groups of Ceramic membrane surfaces showed that ultrasound had a good removal effect on the surface pollutants of Ceramic membrane.The main pollutants on the membrane surface were organic pollution,and a small part of inorganic pollution caused by calcium and magnesium ions;FTIR analysis showed that the main pollutants on the surface of the ultrasound membrane existed in the form of aromatic rings,heteroaromatic rings,alkynes,etc.,while the control group mainly existed in the form of alcohols,aromatic rings,heteroaromatic rings,alkynes,amides,etc;According to Darcy’s law,membrane fouling resistance analysis was conducted,indicating that the control group’s fouling resistance mainly came from cake layer and membrane pore blockage,while the ultrasound group’s fouling resistance mainly came from membrane pore blockage,accounting for 75.53%.On the basis of the previous research,the ultrasonic system,backwashing system,and offline cleaning were combined to further optimize the membrane fouling control effect.After the combination of ultrasound and backwashing,the TMP of MBR remained stable at around20KPa after 20 days of stable operation,and the proportion of membrane pore blockage was45.33%,which was significantly lower than that of the pure ultrasound group;We have developed an efficient offline cleaning technology and selected 0.2%sodium hypochlorite as a chemical cleaning agent.The recovery rate of pure water flux through ultrasonic and offline cleaning is stable at over 90%.SEM results showed that surface morphology of the chemically cleaned Ceramic membrane was similar to that of the new membrane;The contact angle measurement results show that the hydrophilicity of the contaminated film has also been restored after offline cleaning;The bending strength test found that the application of ultrasonic did not have a significant negative impact on the mechanical strength of Ceramic membrane. |
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