Research On The Separation Process And Membrane Fouling Of Disc Ceramic Membrane Treating Different Liquid Systems

With the advantages of environmental friendliness,high temperature resistance,corrosion resistance and low energy consumption,membrane separation technology is widely used in concentration and separation,chemical purification,biological de-bacterization and wastewater treatment.However,membrane contamination is the main problem that limits the efficient application of membrane separation technology.The most effective measure to cope with membrane contamination is by increasing the hydraulic shear on the membrane surface or reducing the transmembrane pressure difference（TMP）.However,for tubular ceramic membranes,increasing the membrane surface flow rate inevitably causes an increase in TPM,which in turn leads to severe membrane contamination.In turn,a low TMP will cause a decrease in filtration efficiency.In addition,traditional ceramic membranes still have limitations for fast separation,deep concentration and selective screening of material systems with high solid content,high viscosity,high added value and wide particle size distribution.Therefore,how to solve the contradiction between high membrane surface flow rate and high TMP,achieve shear strengthening of membrane surface,effectively reduce membrane contamination,and efficiently separate different material systems is the key problem that needs to be solved at present.The disc ceramic membrane has a disc-like shape and is designed with multiple spiral channels inside for permeate collection and outflow.The separation layer is coated on the outer surface of the membrane,and the small molecules enter the spiral channels through the separation layer of the membrane,and the permeate converges and flows out in the hollow central axis.By rotating the ceramic membrane at high speed,high fluid velocity is generated on the membrane surface,resulting in a strong shearing effect,forming a dynamic membrane filtration.In the filtration process,the membrane rotational speed and TMP are controlled separately to achieve high membrane surface flow rate and low TMP filtration,which can effectively homogenize the feed solution and weaken the concentrated polarization layer,inhibit the growth of contamination layer on the membrane surface,and achieve high efficiency filtration.In order to further clarify the separation performance of disc ceramic membranes for different systems,three representative feeds（high solid content ceramic suspension,high viscosity oil-water emulsion,multi-component skim milk）were selected for filtration,separation and concentration by disc ceramic membranes.The filtration characteristics of disc ceramic membranes for different systems under dynamic membrane filtration were analyzed,and the process of membrane separation,membrane contamination type and membrane cleaning were systematically studied to investigate the optimal operating parameters,membrane contamination type and cleaning method of disc ceramic membranes for filtration of different systems.In order to optimize the separation process and improve the separation performance of disc ceramic membranes.The main research results are as follows.（1）The separation of ceramic suspensions with 14 wt%solids using 100 nm disc ceramic membranes achieved a stable membrane flux of 1200 L/（m~2·h·bar）and a rejection rate of 99.3%at a feed fluid temperature of 20°C,a membrane rotation of 292r/min,a TMP of 0.04 MPa,and a gas backwash.Concentration on this basis can concentrate the suspended ceramic liquor to 42 wt%and increase the solid content by 2times.On-line hydraulic cleaning effectively removes filter cake contamination and restores the pure water flux of the membrane to 93%.By increasing the rotation speed of the disc ceramic membrane,it can effectively reduce the thickness of the filter cake layer on the membrane surface and improve the permeate flux,which is very suitable for the separation of suspension liquid system with high solid content and can achieve high flux,low contamination and continuous separation and concentration.（2）Using a 100 nm disc ceramic membrane to treat 1500 mg/L oil-water emulsion,the stable flux of the disc ceramic membrane reached 460 L/（m~2·h·bar）under the operating conditions of feed liquid temperature of 30℃,membrane speed of 365 r/min,TMP 0.02 MPa,backwash pressure of 0.6 MPa,backwash cycle of 6 min and backwash time of 1.2 s.The rejection rate was 99%.The main types of membrane contamination were gel layer contamination and intra-pore contamination.Chemical cleaning and high temperature calcination can effectively remove membrane contamination and restore pure water flux to 98%.At high rotational speed and low TMP,it can effectively cope with the characteristics of droplet rupture and deformation during liquid-liquid separation,reduce the membrane contamination coefficient and improve the flux level.（3）The separation and de-bacterization of skimmed milk using a disc ceramic membrane with a pore size of 1.5μm was able to effectively retain bacteria with a stable membrane flux of 350 L/（m~2·h·bar）and an overall protein transmission rate of more than95%when the feed temperature was 30℃,TMP 0.04 MPa and rotational speed 365r/min.The membrane surface shear generated by the high rotational speed can reduce the concentration polarization layer and gel layer contamination,improve the initial flux,and enable the selective sieve separation to proceed effectively,ensuring the passage of small molecule solutes and the rejection of large particles of bacteria.（4）Disc ceramic membrane and dynamic membrane filtration method have the advantages of large membrane surface flow rate,small TMP,low energy consumption,simple equipment structure and easy disassembly,etc.,which can effectively separate solid-liquid system,liquid-liquid system and colloid system.