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In the membrane filtration processes the fouling phenomena are considered as the major problems in many applications and are caused by various components existing in the feed stream. Countermeasures against the fouling have been studied in terms of the development of anti–fouling membrane materials 1~ 4), pretreatments of feed solution for removing or altering the foulant 5~ 7), and the optimizing of designs of membrane module, processes, and operating and cleaning conditions 8~ 10). The fouling will be caused by physico–chemical interactions between the membrane and foulant and the main interactions are recognized as hydrophobic and electrostatic interactions. The water layer adjacent to the hydrophobic surface has a higher value of free energy than that of the bulk water and adsorption of foulants is favorable because it reduces the total free energy of the system. A water layer next to hydrophilic surface can have a lower value of free energy than the bulk water and it interferes the adsorption of foulants on the surface. The hydrophilic surface modification of membranes has been attempted for applying anti–fouling property to membrane 1~ 4). Electrostatic interactions arise from the interaction between fixed charge and/or fixed dipoles of membrane surface and foulant in aqueous solution. The origin of these surface charges is considered as the adsorption of specific positive or negative ions and/or ionization of specific chemical group on their surface. The charge property of porous membrane can be characterized by zeta potential and the trans–membrane streaming potential (SP) method. Helmholtz– Smoluchowski (HS) equation has been usually used for determination of the zeta potential assuming that the pore has a cylindrical capillary with laminar flow and the surface conductivity and the electro double layer (EDL) overlapping in the pore are negligible 11), *Corresponding author Tel: +81-45-339-3980 Fax: +81-45-339-4012 E-mail: naka1@ynu.ac.jp The response of zeta potential,ζobs, to membrane surface condition and surfactants in solution was investigated from the viewpoint of the interaction between surfactant and membrane surface. Theζobs of three polyvinylidene difluoride (PVDF) microfiltration membranes, which had non–ionic hydrophilic, hydrophobic, and positively charged pore surfaces, with nominal pore size of 0.22μm were measured over wide range of the surfactants concentration. N–Dodecyltrimethyl ammonium chloride (DTAC) and Sodium Dodecyl Sulfate (SDS) were used as cationic and anionic surfactants, respectively. At the lower surfactant concentration (the conductivity below 20mS/m) the behaviors ofζobs mainly depended on the combination of membrane and surfactant used and they can be explained by the interaction between surfactant and pore surface. At the higher surfactant concentration the behaviors ofζobs mainly depended on type of surfactant rather than on membrane used. In the case of SDS the severe flux decline was observed at a certain concentration in all the membranes and the absolute value ofζobs decreased and approached to zero reflecting the flux decline.

【Original Contribution】 Response of Zeta Potential to the Fouling during Microfiltration of Surfactants