Water desalination by forward osmosis: dynamic performance assessment and experimental validation using MgCl2 and NaCl as draw solutes

Abstract Although the FO process steady state performance has been extensively investigated, there is a huge gap in forward osmosis dynamic studies especially for water desalination applications. In this paper, an appropriate dynamic model was developed based on the phenomena involved in the FO process. For its validation, an experimental study was carried out using a FO test bench and flat-sheet membrane for two draw solutes (MgCl2 and NaCl), to measure the water flux, J w , and the reverse solute flux (RSF), J s . The time evolution of these two experimentally obtained fluxes were compared to those calculated using a dynamic model developed using Python language for both draw solute. This comparison shows that the mean absolute error did not exceed 5.25 % for water flux and 5.63% for RSF. The dynamic model can thus be considered reliable when considering experimental errors. The resulting model can thus analyze the influence of the initial draw solute (DS) concentration on both water flux and reverse solute flux dynamics, and subsequently compare the osmotic performances of MgCl2 and NaCl based on the specific RSF ratio. The water flux obtained with MgCl2 is on average 8.23 % lower than for NaCl. MgCl2 nevertheless performed better in terms of reverse solute flux and has been demonstrated to be 28.87 % lower than NaCl. The calculated specific RSF ratio is shown to be independent of both time and DS concentration.