Fouling is the main problem in most applications of membrane technologies for water and wastewater treatment. Fouling can be defined as a decline in flux with time of operation. The flux decline related to fouling is best observed when all other parameters are set to constant values. When the system is operated under constant pressure mode, fouling is indicated by flux decline. On the other hand, transmembrane pressure increase will represent the degree of fouling when the system is operated in a constant flux mode. Resistance and fouling are closely related and the factors affecting resistance also play an important role in membrane fouling. According to most definitions, however, membrane fouling is different from concentration polarization effects and means a decline in flux or an increase in transmembrane pressure that is irreversible unless the membrane is cleaned. This research was to study the treatment of surface water (Bahlui river, Iasi, Romania) using membranes, and fouling process. Two selected membrane types, cellulose acetate membrane with pore size 0.2 µm and polyurethane membrane with pore size 1 µm were used in this study.
