Effect of high and low molecular weight compounds on the behaviour of flux in forward osmosis.

Forward osmosis is a non-thermal membrane process employed for the concentration
of liquid foods at ambient pressure and temperature without deterioration of product as well
as less energy intensive. In the present work, possible mechanism of water transport from
feed to osmotic agent side during forward osmosis in a situation when feed contains high or
low molecular weight compounds and their combination has been presented. Forward
osmosis asymmetric membrane consisted of a very thin semi-permeable nonporous active
layer and a porous support layer. The effects of membrane orientation, mode l (active layer
towards draw solution) and mode 2 (active layer towards feed solution), osmotic agent
concentration on trans-membrane flux during the concentration of pectin and sucrose were
studied. The concentrations of draw solution (sodium chloride) and feed solution (consisting
of pectin and sucrose) were studied. The orientation of membrane was found to significantly
influence the transmembrane flux. The concentration (1.5 to 6M) of osmotic agent solution
when feed solution (pure water) were studied. The mode 1 was found to result in higher flux
values compared to mode2 due to negligible concentration polarization. There was increase
in flux in mode 2 when the feed solution (pectin and sucrose) containing high molecular
weight compounds.