NAMS 2002 Workshop - ICOM 2008

membrane surface characteristics due to the formation of an organic fouling layer
were clearly confirmed by the observed increased hydrophobicity and decreased
surface charge, which could explain the rejection mechanisms of compounds
detected in this study: (1) the main rejection mechanism for the hydrophilic nonionic
compounds was size exclusion, as their rejection remains relatively
constant throughout the experiments. (2) In the case of the hydrophilic ionic
chemicals, the initial rejection mechanism was electrostatic exclusion, which
became offset by size exclusion as fouling occurred. This was explained by the
rejection performances of small compounds declining by 10%, while rejection of
larger chemicals decreased only by 2%. (3) Hydrophobic non-ionic compounds
presented high initial rejection due to their adsorption on the membrane surface.
During long-term operation, their rejection decreased as they were able to diffuse
through the hydrophobic fouling layer.