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Abstract
The use of reverse osmosis in the treatment of
solutions containing a single solute has been the subject
of a great deal of research, but very little attention has
been given to the question of whether the equations developed
to describe the behaviour of single-solute solutions
may be applied to solutions containing more than one
solute. The present work was aimed at testing the suitability
of previously derived transport equations when the solution
to be treated contained two solutes, one organic and
one inorganic. An important point to be decided was the
degree to which interactions between solutes would affect
their rate of transfer through the membrane.
A commercial reverse-osmosis unit was used in the
experimental work. Solution containing a single solute
were tested, as well as those containing two solutes; the
solutes used were sodium nitrate, sodium sulphate, urea and
glucose. Concentrations of ionic substances were measured
by conductivity 5 while liquid scintillation counting was
used to measure concentrations of organic solutes labelled
with radioisotopes. The results of the experiments with
single solutes were necessary for the analysis of the results
obtained with solutions containing two solutes.
The control over experimental conditions and the
accuracy of the measurements were superior to those which
could be achieved under industrial conditions, and were in
no way jeopardized by the use of a commercial unit for such
basic research.
It was found that the transport equations derived
by other workers could be improved upon. In particular, the
equations previously suggested to describe the transfer of
ionic solutes within the membrane were found to be quite inaccurate.
The reason for this inaccuracy seems to be that a
certain amount of the electrolyte solute moves through the
membrane in an undissociated form. A revised set of transport
equations has been suggested.
The interaction between solutes was found in most
cases to be too small to measure. In cases where interaction
was detected it had relatively little effect on the rate of
transfer of the solutes.