Preparation And Characteristics Of Modified Poly(vinyl Alcohol) Composite Membranes

The purpose of this dissertation is to eliminate irreversible membrane fouling and reduce membrane cost of the membrane bioreactor (MBR), the preparation and characteristics of modified poly (vinyl alcohol) (PVA) composite membranes are studied. The PVA with highly hydrophilic character, are used as microfilter modified membrane materials to modify hydrophobic membranes by coating. The PVA thin film composite membranes are prepared with PVA hydrogel layer form on the surface of substrate membranes.The PVA ceramic composite membranes are prepared by coating hydrophilic polyvinyl alcohol and cross-linking agent (glutaraldehyde) on the cheap porous ceramic (SiO₂) membrane. By means of pure water filtration resistance and effect of COD remove in MBR study the effects of various preparative conditions on PVA composite membrane performance. The modified membranes are investigated in MBR to assess their resistance to fouling. The experimental results prove that increasing PVA concentration and coating time, as well as decreasing pore sizes of substrate membranes. All result in increase in filtration resistance and effect of COD remove. In MBR, the modified composite membrane show high anti-fouling characteristics and removal of pollutants compared to unmodified membranes.To improve the hydrophilic character of composite membrane, a new composite membrane which is adopted PVA hydrogel layer as a top layer and non-woven fabric pretreated with polyethylene glyol (PEG-1000) solution as a support layer are prepared. By means of various analysis methods to study the effect of drophilization pretreatment for substrate membrane. The effect of various preparation conditions on PVA composite membranes performance are investigated through the test with pure water flux and protein rejection of composite membrane. In MBR, the change of flux, the removal effect of pollutants and the anti-fouling characteristics of modified membranes are studied. The experimental results show that the hydrophilization pretreatment of substrate membrane is essential for good PVA composite membrane preparations. The anti-fouling characteristics of hydrophobic membranes can be greatly improved by this surface modification method. Increasing PVA concentration and coating time, as well as decreasing pore sizes of substrate membranes, all result in a decrease in flux and an increase in protein rejection. The modified composite membrane with stable flux and high flux recovery revealed significant anti-foulingcharacteristics and removal of pollutants. The modified PVA composite membrane bioreactor has excellent separation characteristics and stable effluent.