Research On Pulsed Cross-flow Filtration Enhancement Technology

Microfiltration technique has been widely applied in biochemical analysis,food processing,wastewater treatment,pharmaceutical and petrochemical industries.However,its further development is limited by the fouling of the filter element.Back-flushing is commonly used in industry to reduce the fouling and increase permeate flux,but the filtration process must be stopped and an additional pump is required to backwash the foulant adhering to the filter surface.Enhanced filtration can also be achieved by vibration or rotation of the filter,which produces high lateral flow rate and high surface shear rates to alleviate concentration polarization.But the filtration system is complicated and difficult for assembling and disassembling.As an effort to solve the problem,this project proposes a filtration enhancement method basing on pulsating flow.The main research work and results are summarized as follows:(1)A negative-differential-resistance(NDR)fluidic oscillator is proposed to enhance the cross-flow microfiltration.The filtration system and key devices such as the oscillator and microfilter are designed and tested.The oscillator can automatically convert a steady flow to a pulsating flow of around 56-115 Hz,amplitude 500-700 k Pa.The combined effects of increased shear rate,membrane scouring and back-flushing can effectively reduce the concentration polarization,prevent micropores clogging,and inhibit the formation of fouling layer.In addition,the oscillator works under constant pressure.In a plug-and-play manner,it can be readily applied to many currently existing filtration systems,and so greatly reducing the mechanical complexity for dynamic filtration.(2)The influences of different working mediums,solution concentration,membrane material,and operating pressure,etc.on filtration performance are systematically studied.For both the aluminum hydroxide suspension and pneumococcus fermentation broth,with the oscillator the filtration efficiency has been significantly improved.The permeate fluxes under500 k Pa are respectively 5.0 and 1.7 times that of the static filtration.(3)The practical application of current method is preliminary tested.As an important processing step in vaccine production,the separation of capsular polysaccharide from the pneumococcus fermentation broth is examined.For 100L feed solution,when convectional filtration is applied,the recovery rate drops rapidly from 39.3%to just 2.0%.In comparison,using the oscillator almost all the capsular polysaccharides can be recovered from the original solution.In the meanwhile,the whole process time is significantly reduced by 31%.The study enriches the strategies for cross-flow filtration enhancement.Relevant findings and results provide useful references for its potential applications.