Two-stage FO-BWRO/NF treatment of saline waters

Abstract

Two-stage forward osmosis (FO)–reverse osmosis (RO)/BWRO and conventional RO/BWRO processes were evaluated for saline water treatment. Three different salts, NaCl, MgCl₂ and MgSO₄, were used as a draw solution. The performance of FO, RO and BWRO regeneration processes was simulated using predeveloped software. The simulation results showed that the water and solute flux across the FO membrane decreased with increasing the FO recovery rate. The highest water flux was in case of 1.2 mol NaCl draw solution for seawater desalination. The total power consumption for seawater desalination was lower in the RO process than in the FO–RO process. However, as the RO recovery rate increased, the difference in total power consumption between the conventional RO process and 0.65 mol MgCl₂ FO–RO processes was insignificant. In case of brackish water desalination, the lowest specific power consumption and permeate TDS were in case of the conventional BWRO process and then followed by 0.32 mol MgSO₄, 0.22 mol MgCl₂ and 0.33 mol NaCl FO-BWRO processes. However, the specific power consumption of RO-BWRO process dropped to less than that in the conventional BWRO process when NF membrane was used for MgSO₄ regeneration and water extraction. In general, the high recovery rate can be achieved by the FO–RO/BWRO process which is particularly important especially in case of inland desalination.

Keywords:

• Forward osmosis
• Desalination
• Reverse osmosis
• Brackish water desalination
• Two-stage desalination

Acknowledgement

Authors would like to acknowledge the Carnegie Trust [grant number 31823] to support this research study.