The Experimental And Model Study On Microfiltration Of Submerged Hollow Fibre Membrane Modules

MBR is an original kind of reactor which combines the process oftraditional bio degradation and high efficient membrane separation. With thevirtue of small area covered, easy operation, low upfront cost and human cost,MBR has been more and more widely used in waste water treatment. However,factually, the problems cause by the membrane fouling, such as, the flux ofwaste water treatment decreasing, energy consumption increasing, frequentflashing membrane and the reducing of membrane using life, can all raise thecost of use MBR. So, it is necessary to investigate the process of submergedmicrofiltration and find a way to control the membrane fouling.Introducing air bubble in MBR proceeding not only can provide oxygenin the process of bio degradation but also wash and disturb the surface ofmembrane, which can decline the cake deposition rate and control themembrane fouling. The membrane fouling is affected by the way of airbubbling conditions and different membrane modules. As a result, in this study,the membrane fouling for different way of introducing air bubble and differentmembrane modules were investigated. What's more, a model describing the membrane fouling in this process was proposed and compared withexperiment results.The waste water was representing by yeast suspension in the experimentand the trans membrane pressure at the outlet of membrane with constanttrans membrane flux was observed under different operating conditions. Theresults showed:(1) Way of gas bubbling. Compared with dead end filtration,cross flow filtration with gas bubbling could decrease the increasing rate oftrans membrane pressure and control the membrane fouling. Thetrans membrane pressure increasing rate with different gas flow rates wasobserved and found that the trans membrane increases more and more slowlywith the increase of gas flow rate. However, the efficiency of this way reducedwith the rising of gas flow rate. The influence of air inlets distribution atbottom on trans membrane pressure was investigated. The results showed thatthe trans membrane pressure with air inlets concentrated distributionincreased more slowly than that with ones discrete distribution. Multinozzleconcentrated distribution was slightly better on control membrane fouling thansingle nozzle concentrated distribution. Large size of air inlets were better oncontrol membrane fouling than small size of air inlets. However, thisdifference became very small under high gas flow rate.(2) Differentmembrane modules. With constant filtrate flow rate, the increasing rate oftrans membrane pressure decreased with number increasing of membranesilks in the same area. Under the same air flow rate, looser membrane silks were beneficial to control membrane fouling and the effect of fouling controlwas better under high gas flow rate. Under the same air flow rate and the sametightness, long fibre's amplitude is higher than looser one,but frequency waslower than looser one. The long fibre silk increasing rate of trans membranepressure was lower than short one.Microfiltration processes were divided into the membrane in water, theaverage flux less than the critical flux and average flux greater than the criticalflux models. By Hagen Poiseuille equation deduced in water, it found thatflux of the top silk was the maximum along the silk membrane. When theaverage flux was less than the critical flux, trans membrane pressure would beeventually constant. Assuming, the critical flux was the same along the silk,the results of flux along the fibre can be concluded. When the average fluxwas greater than the critical flux, after trans membrane pressure zero growth,the cake grew in the same flux. The experimental data was close to modelingdata.