Membrane fouling is inevitable and is still a major impediment to broader application of membrane technology. Many studies have been conducted to improve membrane performance by regulating and controlling the effect between membrane surface and coagulation flocs/particles. In the present study, different kinds of alum flocs or iron flocs were pre-deposited onto the flat sheet ultrafiltration (UF) membrane surface to test their anti-fouling properties. The results showed that alum flocs alone performed better on removing humic substances (humic acids, HA) or protein (bovine serum albumin, BSA) in comparison to that of iron flocs alone. When different mole ratios of the mixed FeCl3/AlCl3 flocs were pre-deposited onto the membrane surface, membrane performed better in the presence of higher mole ratio of alum. For AlCl3 flocs, the characteristics were significantly influenced by solution pH. Although the fractal dimension of alum flocs was smaller under lower pH conditions, their particle sizes were much smaller, resulting in a denser cake layer on the membrane surface, of which the roughness was larger. In addition, the positive charge of alum flocs under lower pH values was higher, and negatively charged HA or BSA molecules were easily to be adsorbed. Further research was focused on the hollow fiber UF membrane, of which AlCl3 flocs were pre-injected by air sparging in membrane tank. HA could also be largely removed and the corresponding membrane fouling was alleviated. Membrane performance was easy to be influenced by the concentration of alum flocs, air sparging position, air sparging mode and injection mode of flocs, etc. The more alum flocs were injected, the better the removal efficiency was and the membrane performed. When the position of air sparging was far away from the bottom of the membrane tank and intermittent aeration was used, plenty of alum flocs could be settled, and could not be made full use. When the position of air sparging was on the bottom of the membrane tank and continuous aeration was used, alum flocs could be well suspended in the membrane tank and membrane fouling was less serious. In addition, membrane performed worse once alum flocs were injected only one time, owing to more alum flocs “aged”.

Ultrafiltration membrane purification efficiency and mechanism with the synergistic effect of flocs

251st National Meeting (2016)

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