Rejection of nine haloacetic acids and coupled reverse draw solute permeation in forward osmosis

• Forward osmosis rejects haloacetic acids (HAAs) well.
• The active-layer facing feed water (AL-FW) orientation is preferred.
• The solution-diffusion model predicts HAA rejection better for AL-FW.
• The solution-diffusion model accurately predicts reverse draw solution permeation.

The rejection of haloacetic acids (HAAs) by forward osmosis (FO) and the coupled reverse draw solute permeation were experimentally determined and mathematically modeled by using the solution-diffusion model for both the AL-FW (active layer facing the feed water) and the AL-DS (active layer facing the draw solution) orientations. The rejection ratio for each HAA increased with the increase of draw solute concentration for the AL-FW orientation. In contrast, the HAA rejection ratio could reach its maximum under a medium osmotic pressure difference for the AL-DS orientation. The rejection ratios for all HAAs were higher than 94.6% for the AL-FW orientation and ranged from 73.8% to 89.1% for the AL-DS orientation under a draw solute concentration of 1 mol/L NaCl. The reverse draw solute flux for the AL-FW orientation was lower than that for the AL-DS orientation. The model-predicted HAA rejection results matched well with the experimental rejection ratios for the AL-FW orientation. However, the model over-estimated the rejection ratios for the AL-DS mode, likely due to the adoption of inaccurate mass transfer coefficient for internal concentration polarization. Regarding the reverse draw solute permeation, a general agreement between the model prediction and experimental data was observed for both orientations.

The behaviors of haloacetic acid (HAA) rejection by forward osmosis are obtained by experiments and predicted by the solution-diffusion model combined with concentration polarization for both the AL-FW (active layer facing the feed water) and the AL-DS (active layer facing the draw solution) orientations.Figure optionsDownload as PowerPoint slide