The performance of the spiral wound and flat sheet forward osmosis elements with thin film composite membrane

摘要

The two different types (flat sheet and spiral wound) of commercial forward osmosis (FO) elements with thin film composite membrane were tested to understand the effects of concentrations and cross-flow velocities of feed solution (FS) and draw solution (DS) on the performance of the element. An FO element tester was customized for reliable measurements of water flux and reverse solute flux during operation time when the concentration difference between DS and FS was decreased. The test results reveal that: (1) the water flux and reverse solute flux increases at higher concentration differences between FS and DS, (2) the higher crossflow velocity increases water flux by decreasing the effects of external concentration polarization, (3) the pressure differential between the inlet and the outlet of the FO element increases at higher crossflow velocities, which may limit the crossflow velocity in a full-scale FO design, (4) the flat sheet element exhibits up to 25 LMH of water flux comparable to the water flux (30-35 LMH) in the coupon tests, and (5) the spiral wound FO element shows a peculiar flux pattern in which the increasing rate of water flux becomes retarded when water flux exceeds a critical value maybe because the DS channel in the FO membrane envelop may not allow a flow rate higher than a critical value due to complexity in the DS flow direction.