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Water Science & Technology: Water Supply Vol 1 No 4 pp 49–56 © IWA Publishing 2001

Fouling mechanism of hollow fiber ultrafiltration membrane with pretreatment by coagulation/sedimentation process

S. Minegishi*, N.-Y. Jang**, Y. Watanabe***, S. Hirata**** and G. Ozawa*****

*Global Environment Research Laboratory, Pioneering Research Laboratories, Toray Industries, Inc., 2-1 Sonoyama 3-chome, Otsu, Shiga 520-0842, Japan
**Department of Urban and Environmental Engineering, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku Sapporo 060-0813, Japan
***Department of Urban and Environmental Engineering, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku Sapporo 060-0813, Japan
****Water Treatment Plant Engineering Department, Environmental Control Plant Division 1, Kawasaki Heavy Industries, Ltd., Kobe Crystal Tower, 1-3 Higashi Kawasaki-cho, 1-chome, Chuo-ku, Kobe 650-91, Japan
*****Department of Urban and Environmental Engineering, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku Sapporo 060-0813, Japan


ABSTRACT
The fouling mechanism of the hollow fiber UF membrane with a pretreatment by coagulation/sedimentation process was investigated. The experiments were carried out in three different feed water conditions: river surface water, coagulated water containing micro flocs and clarified water from the coagulation/sedimentation process. The river water contained a lot of suspended particles (high turbidity) and natural organic matter (NOM) such as humic substances. From analysis of the data obtained in the three membrane processes, the mathematical model expressing the change of the filtration resistance is proposed and proved, which includes the pore size distribution of the membrane. The effect of DOC and DOC/E260 on the membrane fouling was also discussed. The analysis of the pore size distribution change with increasing filtration time suggests that the primary mechanism of the fouling is the decrease in the pore number by the high molecular weight humic substances. As a result of experiments and mathematical model analysis, it could be concluded that the coagulation/sedimentation pretreatment process was very effective for expanding ultrafiltration membrane life, because the coagulation/sedimentation process could remove the primary foulants such as high molecular weight humic substances.

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