Research Of Preparation Hydrophilic Microporous Poly (Vinyl Alcohol) Composite Membrane And Application In The MBR Treatment Wastewater

The membrane bioreactor (MBR) uses the combine of membrane separating technology and biological treatment to treat industrial wastewater, its process is relatively simple, footprint is small, the amount of excess sludge is less, the water quality is good and the automatic degree is high. The technology is widely used in different areas, water treatment technology researchers in many countries have concern on it. But high cost of membrane filtration modules and membrane fouling are the main factors that restrict the better development of membrane bioreactor. So studying how to reduce the cost and membrane fouling has very important significance for the development of membrane bioreactor.This paper studies how to make low-cost, resistant to pollution composite membrane and its function direct its high cost and membrane fouling. We choose polyvinyl alcohol that price is relatively cheap, and we use thermally induced phase separation to make composite membrane, then make it soak glutaraldehyde so we get hydrophilic sexual of microporous composite membrane. The main contents are as follows:(1) Experiment investigated the influence of the four different factors that affect membrane performance-concentration, the temperature of heat treatment, concentration of the cross-linking agent and cross-linking time. The results show that the best and most condition (concentration is12%, concentration of the cross-linking agent is1%, cross-linking time is6hours, the temperature of heat treatment is80～90℃) can make good hydrophilic sexual of microporous composite membrane. The number of hydroxyl groups reduce after crosslinking and water resistance of composite membrane is improved.(2) In this paper we characterize composite membrane and determinate water flux. Experiments show that when the concentration is10%, the pore of the surface is relatively open, but the pore size is too large, and the average pore size of surface is about0.45μm, its pore structure is substantially symmetrical structure. The surface of membrane has phenomenon of skinning when the concentration is13%, and the aperture of cortical pore is approximately0.2μm. Water flux increases with pressure in the water column of0.5-2m, the average water flux is408.3L/m2·h in the water column of1.5m. the surface contact angle of10%composite membrane is42°, the surface contact angle of13%composite membrane is39°.When the concentration is low, the crosslink density is relatively small, The polar group such as hydroxyl group is easy to segregate at the surface. the crosslink density increases with concentration, the segregation of polar group is affected, and the change in contact angle is flatten. Dry membrane become wet when met water, and its hydrophilic property is excellent, the membrane made in laboratory has a good anti-pollution and water permeability. The flux of composite membrane that soaked with acid donnot decline obviously, it has good acid resistance, and the flux don’t change over time. This shows that the membrane has a certain acid resistance and is suitable for chemical acid cleaning operation.(3) We made MBR using hydrophilic sexual of microporous composite membrane to treat formulated domestic sewage and study its running effect and membrane fouling. Experimental results show that turbidity is increasing then reducing with running time, the turbidity is0.12-0.21. Hydrophilic of increasing could reduce resistance of filter, the rate of membrane flux declining slows, The anti-pollution ability of membrane increase..Under certain pressure that through the membrane, the flux decay curves are similar in different concentration of activated sludge, the decay margin of flux increase fastest in the concentration of3500mg/L, it can reach75.9%. Aeration intensity is too small or too large will cause significantly changes in membrane flux. Selecting suitable aeration intensity can delay membrane fouling. The experiment shows that0.4m3/h is the best aeration intensity, and it can effectively delay pollution and maintain better membrane flux. The recovery rate is above90%after the membrane pass through water backwash and water backwash+the aeration cleaning, it means the flux recovery performance of hydrophilic sexual of microporous composite membrane is good. In addition, after repeating the aeration cleaning and water backwash, the surface of the membrane has not been destroyed, that fully explains the high strength and strong shock resistance of this membrane.