The forward osmosis application: using the secondary effluent as makeup water for cooling water dilution

This study evaluated the feasibility of using the secondary effluent as makeup water for cooling water. The secondary effluent and the simulated cooling water were used as feed solution (FS) and draw solution (DS) in FO process. Ammonium bicarbonate was added into the simulated cooling water to promote the osmotic pressure. The tests were studied under different membrane orientations, temperatures and flow rates using both TFC-FO and CTA-FO membranes, and determined in terms of water flux, the permeate recovery and membrane fouling. The considerable permeate recovery (18.9% at 20 h) and reversible membrane fouling indicated that the feasibility of using FO for cooling water reuse. CTA- and TFC-PRO modes had higher initial water flux, but more significant flux decline compared to CTA- and TFC-FO modes. The optimal conditions were determined to be 25 degrees C and 17.0 cm/s in which the water flux was highest. The results showed that water flux did not increase with the temperature when it was above than 30 degrees C. The same situation occurred at the cross flow velocity above than 17 cm/s. The fouling of TFC membrane was serious after running 20 h, but it could be cleaned well by 1 h simple surface flushing and the water flux could restore nearly 93.8%.