NAMS 2002 Workshop - ICOM 2008

of feed water ionic strength) on rejection was also investigated and incorporated
into the mathematical model. Results suggest that, in contrast to the rejection of
inorganic solutes, the Donnan-exclusion mechanism does not seem to play a role
in the rejection of charged organic solutes. The models for uncharged and
charged solutes were then combined into a general rejection model for organic
solutes in aqueous solutions. Using mass balances, this general rejection model
was then extended to a mathematical expression for the rejection of organic
solutes in full-scale installations.
The full-scale rejection model was tested and validated by spiking a cocktail of 25
pharmaceutically active compounds and pesticides on a 2 stage pilot installation.
The pilot scale installation contained 18 4-inch membrane elements (12 in the
first stage, 6 in the second stage) and was operated during 2 different runs at
75% and 83% recovery. During these runs, permeate samples of the different
stages and of the first and last membrane element were collected and analysed
for pharmaceuticals and pesticides. This way, rejection values at different
recoveries could be determined and compared to the modelled rejection values.
The modelled rejections seemed to correspond to the measured full-scale
rejection values at different recoveries quite well.
Results obtained in this study may prove to be very useful for future applications
of membrane filtration for potable water purposes. The derived models may
provide an a priori evaluation of the performance of a full-scale membrane
filtration plant: based on selected parameters of solute and membrane, the
rejection of an organic solute with a full-scale NF/RO plant can be estimated.