Preparation And Characterization Of Novel Precoating Regent In Dynamic Membrane

The membrane bioreactor (MBR) is a new technology combined the wastewater biological treatment with the membrane separation technique, it showes great potential application in the wastewater treatment field. However, membrane fouling is a problem restricting the wild application of this process. Precoated dynamic membrane technology is used to modify membrane properties, which based on the membrane fouling mechanism: precoating regents were adsorbed on the surface or inner channels of membrane, so it can not been direct contact with fouling materials and its serving life was prolonged. Thus, it is necessary to prepare a novel precoating regent with anti-fouling characteristics to settle the problem of membrane fouling.In this thesis, cross-linked polyvinyl alcohol microspheres were prepared via an emulsion polymerization that PVA cross linked with glutaraldehyde which was extracted by anhydrous aether. Effects of concentration of PVA solution, the volume ratio of aqueous phase to oil phase, the selection of surface active agent (SAA) and its concentration on the stabilization of emulsion were studied. The results showed that:(1) When the concentration of PVA solution was 2.7%, the volume ratio of PVA solution/n-heptane was 40:60 and the concentration of span-80 was 1.30g/dL, the stirring speed 7000r/min with 10min, the emulsion was stabilized. Glutaraldehyde as a cross linker was dropped into the emulsion. After 3h cross-linked reaction in the condition of 50℃water bath heating and continuous stir, monodisperse PVA microspheres which contented our needs were prepared. The size of microspheres was 1850±100nm. The Zeta potential in the rage of -44mV--41mV , and the contact angle of PVA microspheres with distilled water was 16°-19°.(2) The size of microspheres diminished with the stirring speed increasing under the condition of enough span-80. It became smaller with the accretion of an aimed cross-linking degree which has little affection on surface charge. The contact angle of PVA microspheres with distilled water showed that these microspheres were hydrophilic.(3) The FTIR results suggested that hydroxy groups were great intensity with 100% of aimed cross-linking degrees and aldehyde group were residualed on the PVA microspheres.In order to further promote its anti-fouling characteristic, NaBH₄ was used to deoxidize aldehyde groups and the amber acid was grafted on the surface of PVA microspheres. The test methods and the characteristics of the modified PVA microspheres were investigated. The results showed that:(1) NaBH₄ was dissolved in anhydrous ethanol, and then reacted with PVA microspheres in ice-water bath for 3h. The mole ration of NaBH₄ and aldehyde group was 10:1. After reaction, PVA mirospheres modified by NaBH₄ were prepared. The number of hydroxy groups on the surface is improved from 2.11×10²⁰/g to 2.60×10²⁰/g.(2) Amber acid was dissolved in acetonitrile, and then reacted with PVA microspheres in the condition of heating reflux. The mole ration of Amber acid and hydroxy group was 10:1. The reaction reached equilibrium after 9h. PVA mirospheres modified by amber acid have a good anti-fouling characteristic to BSA.