| As a new high-tech, membrane technology has been widely used in purification, concentration and separation. It has become the basis of resolving energy, resources, environmental pollution, and sustainable development in the contemporary times. From the technology perspective, the membrane technology will come into a period of development, and will become one of the ten high-techs and one of the six new technologies in leading the coming industry in the 21st century. However, its lower output, easier to be polluted, and higher price seriously prevent its application and development.Based on the design concept that the membrane structure and performance could be improved by adjusting the compatibility between polymer blends, a new kind of blend fine-hole hollow fiber membrane was prepared. The novel hollow fiber membrane with big water flux, high intension and lower price was prepared. The hollow fiber membrane possesses five-hole, with its main components three types of polymer components-polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC), in casting solution prepared using two kinds of additives-PVP and alumina. The novel membrane was employed to fabricate membrane module of membrane bioreactor (MBR) and the printing and dyeing wastewater was treated by the PAC-MBR process.The following studies were carried out on compatibility of PVDF/PMMA/PVC, the influence factors in casting solution and process, and those in spinning and precipitation process, etc. The anti-fouling property of PVDF/PMMA/PVC hollow fiber membrane was also studied when treating printing and dyeing wastewater. PVDF/PMMA/PVC blend membrane was made into MBR used for treatment of reactive blue KN-R wastewater. In terms of the innovation and theoretical value, the following aspects are among the most telling:1. The compatibility of PVDF, PMMA and PVC was analyzed by means of△Hm, FTIR, Differential Scanning Calorimetric method, and Solution Viscosity method. It was shown that PMMA/PVC possesses complete compatibility; PVDF/PMMA/PVC possesses partial compatibility which is depended on and influenced by the blend ratio, concentration of polymers in casting solution, temperature, etc. The compatibility in PVDF-rich phase is greater than that in PVC/PMMA-rich phase. The compatibility was better when polymer concentration of 16%-18%, PVDF:(PMMA+PVC) of 70:30, PMMA:PVC of 3:2, and solution temperature of 80℃.2. The factors that affect the viscosity, and compatibility of the casting solution, such as the dissolution temperature, polymer concentration, additives, the blend ratio of PVDF:(PMMA+ PVC) and PMMA:PVC, were studied, then the suitable composition of the casting solution was determined. By examining the property of the five-hole membrane, that is, the tensile strength, tensile multiple, water flux, retention, cross section and surface structure, the influence of casting solution composition on membrane properties of five-hole was researched.(1) The results indicated that the membrane with PVDF:PMMA:PVC mass ratio 7:1.2:1.8, polymer concentration 17%, and with the ratio of PVP 6%, alumina 1%, the membrane with excellent performance could be prepared.(2) The surface of membrane made from PVP as additive was smoother than that made from Tween 80 or PEG 1000. The viscosity of casting solution could be increased to different degrees by the addition of three non-ionic surfactants. With the increase of surfactant concentration, the viscosity of casting solution increased first, and then decreased when the viscosity was to the maximum. The maximum flux of blend membrane prepared from PVP was superior to that of Tween 80 or PEG 1000, the mechanical properties also had a greater advantage.(3) The flux of PVDF/PMMA/PVC five-hole blend membrane could be improved by nano-Al2O3, but did not affect the basic membrane rejection. The result of SEM of the cross-sectional of the membrane showed that the formation mechanism of PVDF/PMMA/PVC blend membrane couldn’t be changed by Al2O3 accession, and the microstructure of the membrane wasn’t been affected either. The addition of inorganic nano-Al2O3 particles effectively improved the toughness and strength of the membrane, and when the quantity of nano-Al2O3 was 1%, the tensile strength could be about 9.2MPa.3. The spinning factors that influence the performance of five-hole membrane were studied, including coagulation bath agent, coagulation bath temperature, bore liquid agent, bore liquid velocity, dry spinning gap distance, spinning pressure, etc. and the suitable experimental data was obtained.(1) The effect of composition of coagulation bath on the structure and performance of the hollow fiber membrane remarkably. The water flux increased when DMAC in a small amount in the coagulation bath. The water flux reached the maximum when the concentration of DMAC was 20%. However, the retention of the five-hole to BSA is relatively small in the same time. The suitable water flux and rejection to BSA of the five-hole membrane were achieved when the concentration of DMAC was 10%. The structure of the outer wall of membrane would be dense when DMAC concentration was more than 20%. The structure following the outer wall was the finger-like structure, and the lowest level for the wall was network structure. The gel-coagulation process was delay separation ones. The sectional structure changed from the obvious finger-like to the sponge-like pore structure. Water flux and the intensity were smaller.(2) The water flux would be affected by the coagulation bath temperature to a certain extent. The flux and rejection rates could be maintained at high levels when coagulation bath temperature was appropriate. The temperature of the coagulation bath would be controlled at 25℃～35℃,(3) With the increase of the bore fluid flow, the outer diameter of hollow fiber membranes increased, and the diameter increased faster than the outer diameter, which makes the outer wall thickness of five-hole blend membrane decreases. As the thickness decreased, the water flux increased, however, the rejection decreased. The suitable bore flow should be 8-15mL/min. when DMAC concentration of the bore solution was 10～40%, the membrane prepared possessed higher flux.(4) Flux could be increased when the air gap was proper, which should be relative to the solvent evaporation and moisture to casting solution. Flux had a higher value with the air-gap of 13～25cm, and flux decreased when air-gap was greater than 25cm. Because the strong moisture absorption of DMAC in air, leading to the rate of moisture absorption to casting solution faster than that of evaporation of DMAC, the flux increased with the increase of air-gap. Dry-spinning process is greater than 25cm, The absorption rate was smaller than evaporation rate when air gap was longer than 25cm, which leading to dense surface structure and smaller flux.(5) The effect of pressure on the property of prepared five-hole membrane was not obvious. The spinning pressure could be latm.The optimum spinning conditions of preparing five-hole PVDF/PMMA/PVC membrane were as follows:the 10～20% DMAC solution as coagulant, coagulation bath temperature of 25～35℃, the bore solution concentration of 10～40% DMAC, the bore liquid flow of 8～15mL/min, the air gap of 13-25cm, the spinning pressure of latm. Under these conditions, the five-hole membrane was produced with better performance of the intention as 9.2MPa, tensility as 1.50, flux as 526L/m2·h, and retention ratio as 89%.4. PVDF/PMMA/PVC blend hollow fiber membrane with NaClO solvent post-treatment was studied and the results indicated that post-treatment with NaCIO can enlarge the micropore on membrane surface, and, therefore, increase water flux significantly. NaCIO had no distinct influence on membrane aperture size, which resulted in retention remaining stable between 82% and 89%. The loss of weight of five-hole blend hollow fiber membrane was below 2% after membrane dipped in both acid and alkaline solution. Acid and alkaline soak had little effect on mechanical property. The results showed that PVDF/PMMA/PVC blend hollow fiber membrane possessed good ability of resistance to acid and alkali in the broad pH range. The membrane flux declined as the filtration time increased, followed by 60 minutes with a steady value in latm. After the fouled membrane was cleaned by water, the flux recovery of membrane with additives was higher than membrane free additives. It was shown that PVP and alumina can improve hydrophilicity of membranes. Membranes modified by PVP and alumina had a more favorable antifouling performance and can be applied in wastewater treatment.5. MBR process was applied into the treatment of reactive KN-R printing and dyeing wastewater while the PVDF/PMMA/PVC five-hole hollow fiber membrane was used in MBR process. Based on the running result and treatment effect, the main parameters such as influent COD, HRT, MLSS, and SRT were optimized by means of orthogonal regression function. The effect of activated carbon powder(PAC) on MBR, the degradation mechanism of organic in printing and dyeing wastewater, the antifouling result, and the suitable time of sludge removal were also studied, and then the regression equation of the influent COD, HRT and MLSS was achieved.(1) The suitable operation parameters of MBR were HRT of 24 hours, COD of 900mg/L, MLSS of 11000mg/L.(2) Non-biodegradable organic Sn=50.211mg/L, substrate removal rate constant K=8.42L/g.d, maximum specific degradation rateμmax=0.92d-1, saturation constant Ks=0.092g COD/L. The PAC-MBR process possessed certain advantages compared with the constants of treatment process of incomplete anaerobic or aerobic technology.(3) PAC-MBR combined process is highly efficient in treating printing and dyeing wastewater. The interception of membrane bioreactor can make the MBR work efficiently not only to the high volume load, low sludge load, but also to the treatment effect of MBR. The addition of PAC can not only effectively adsorbed dissolved organic matter, and can reduce the density of sludge, effectively alleviate membrane fouling process, reduce system power consumption during operation.(4) Membrane contamination concentrated in the outer membrane surface. Gel layer can increase the number of the membrane filtration resistance. The main cause of membrane fouling is the cake layer and gel layer in membrane surface.(5) The PVDF/PMMA/PVC membrane used to treat printing and dyeing wastewater was been cleaned by HCl, NaOH and H2O2, and the cleaning effect was compared. The effect of membrane cleaned by H2O2 was better than that of HCl or NaOH. The recovery rate of flux was more than 80%, and the surface structure was nearly recovered... |
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