IMPACT OF CELL SURFACE CHARACTERISTICS ON MEMBRANE FOULING Jang-Hyun Lee*, Seok-Tae Kang**, Yong-Tae Ahn***, and Hang-Sik Shin*** *Daewoo Institute of Construction Technology JangHLee@dwconst.co.kr 60 Songjuk-dong, Jangan-Gu, Suwon, Gyeonggi-Do 440-800, Korea **Department of Chemical Engineering, Environmental Engineering Program, Yale University ***Department of Civil and Environmental Engineering, KAIST ABSTRACT Initial deposition of S. cerevisiae particle to plate type membrane was conducted with direct observati on system(DOB). Solution chemistry was controlled by ionic strength variation(0mM ~ 50mM) with N aCl, MgCl 2 , CaCl 2 . Predictable tendency by DLVO theory was that increment of ionic strength make in teraction forces decrease and make it easier to be attached to membrane, finally. Although DLVO mod el missed the effect of ion valency, test results showed that divalent ion was more powerful than monov alent ion in reducing interaction forces between particles. Attachment test showed good agreement with model result, so increment of ionic strength make detach ment rate decreased. But existence of extracellular polymeric substance (EPS) resulted in difference bet ween detachment experiment and DLVO prediction values. EPS removed yeast exhibited somewhat slo wer detachment rate by increasing cross flow velocity when compared to the raw yeast cells Yeast parti cle has softness characteristics by Ohshima’s soft particle theory which can be applied almost microorg anisms. This DLVO theory modification help to predict the behavior of microorganism in membrane sy stems more precisely by including the effect of EPS structure. KEYWORDS biofouling, DLVO theory, direct observation(DOB), soft particle theory, initial deposition INTRODUCTION Membrane biofouling Biofilm growth is a major problem in membrane coupled water and wastewater treatment processes be cause it leads to higher pressure loss, chemical cleaning and shortened membrane life. Among the vario us stages of membrane fouling, initial deposition is the most important step as the formation of foulant layer on membrane surface is progressed in order of initial deposition, EPS growth and stabilization. 2725 WEFTEC®.06 Copyright 2006 Water Environment Foundation. All Rights Reserved ©