Influence of concentration polarization on flux behavior in forward osmosis during desalination using ammonium bicarbonate

Forward osmosis is recognized as one of the promising membrane based desalination process and viable alternative to reverse osmosis as a lower cost and more environmentally friendly desalination technology. The solution of ammonium bicarbonate was used as a draw solution to extract water from a feed containing 0.5 M sodium chloride. The water was transported from feed to draw solution and it can be recovered upon moderate heating of the draw solution, which is decomposed into ammonia and carbon dioxide gases producing pure water. The mechanism of water transport in the case of feed containing pure water or sodium chloride has been elucidated depending upon the orientation of the membrane. The concentrative and dilutive internal concentration polarizations played a major role in a situation when feed was towards support layer and feed was towards active layer, respectively. For the desalination applications, the feed towards support layer was found to be best mode to achieve higher flux. An increase in draw solution concentration from 1.0 to 3.6 M, resulted in an increase in flux values from 0.58 to 1.39 × 10− 6 m3m− 2 s− 1 at 30 °C. Further, an increase in temperature of the draw solution from 30 to 45 °C resulted in increase in transmembrane flux from 1.39 to 2.11 × 10− 6 m3m− 2 s− 1 at the highest draw solution concentration. It was concluded that forward osmosis can prove to be a feasible technique for the recovery of water from saline water.

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► Mechanism of water transport for two different modes has been elucidated.
► Resistivity values have been determined for two different modes.
► Feed towards support layer was found to be the best mode for desalination.
► Forward osmosis was found to be a feasible technique for recovery of water.