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Abstract
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The present study aims to investigate the properties, identification, and comprehension of the obstacles
encountered in the forward osmosis process when utilizing a hydrogel drawing agent (FO-HG). Furthermore, a
comparison is made between the FO-HG system and conventional forward osmosis systems employing a salt
solution drawing agent. The comparison and evaluation of the swelling process of hydrogel and the kinetics of
water penetration are conducted in both un-constrained and constrained states. Furthermore, the investigation
and analysis are carried out to determine the presence or absence of internal concentration polarization (ICP) and
external concentration polarization (ECP) phenomena. These phenomena are studied in situations with and
without mixing, as well as in different orientations of the membrane (FO-mode and PRO-mode). The impact of
these phenomena on the water flux of the systems FO-HG and FO-NaCl is also examined. An evaluation is
conducted to determine the influence of the amount and size of hydrogel used as a draw agent in the FO-HG
system on the water flux. The results of the study reveal that smaller hydrogel particles in the FO-HG system
exhibit a higher flux compared to larger particles. Additionally, it is observed that the water flux in PRO-mode is
unexpectedly higher when salt water is used as feed solution. This phenomenon can be ascribed to a counterosmotic
effect, originating from the FO state. Despite the high water absorption capacity of hydrogel and its
potential as an ideal drawing agent in the forward osmosis process, the results demonstrate that the flux of the
FO-HG system is inferior to that of the FO-NaCl system. Finally, the focus is on resolving the low flux issue by
suggesting a process involving multiple cycles throughout day and night. We investigate the influence of
hydrogel particle size, membrane surface, hydrogel layer thickness, as well as swelling and deswelling time in
one cycle. The swelling time displays a peak at
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