Factors influencing on permeate flux in membrane-separation activated sludge process

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In activated sludge process with membrane filtration, complete solid-liquid separation is achieved and operation with high organic load can be applied. Especially, system with submerged membrane separation is expected as an excellent membrane-separation system because of its energy-saving and cost-effective performance. However, factors influencing on the permeate flux in this system have not been clarified yet. This study was conducted to investigate the influence of initial operating permeate flux and air bubbling volume on permeate flux in the system. The strength of air bubbling was expressed as "superficial velocity", defined as an air volume divided by a cross section of bubbling area. In addition, batch filtration tests were conducted to investigate the mechanism of membrane fouling.Permeate flux was set up at 0.18, 0.36 or 0.72 (m/day) in the beginning of operation with a constant superficial velocity of 0.88 (m/min). As the initial flux was higher, the rate of flux drop was higher. This was caused by increment of resistance of cake and gel layer (Rcg) onto the membrane surface. It was shown that surplus superficial velocity of 1.76 (m/min) had an adverse effect on permeate flux when the initial flux was 0.72 (m/day), by forming a firm fouling layer onto the membrane surface.Currently, the effect of sludge load in operation on permeate flux is been investigated.