Brackish water desalination by a hybrid forward osmosis–nanofiltration system using divalent draw solute

In the last decade osmotically driven membrane processes have attracted growing interest in wastewater treatment, desalination and power generation. A hybrid forward osmosis–nanofiltration (FO–NF) system designed for brackish water desalination was systematically investigated in this study. The hybrid FO–NF process was also compared with a stand-alone reverse osmosis (RO) process in brackish water desalination. It is found that the hybrid FO–NF process has many advantages over the stand-alone RO process in brackish water desalination, such as lower hydraulic pressure, less flux decline caused by membrane fouling and higher flux recovery after cleaning. Other benefits like no pre-treatment requirement, higher permeate quality and no need for chemical cleaning in brackish water desalination can also be achieved by the hybrid FO– NF system. Therefore, the proposed FO–NF system using a divalent draw solute (e.g. Na2SO4 or MgSO4) can be a useful alternative to stand-alone RO processes in brackish water desalination. © 2011 Elsevier B.V. All rights reserved.

Brackish water desalination by a hybrid FO–NF system was systematically investigated in the current study. It is demonstrated that the hybrid FO–NF system using Na2SO4 draw solution can be used in brackish water desalination. The hybrid FO–NF process was also compared with a stand-alone RO process in brackish water desalination. It is found that the hybrid FO–NF process has many advantages over the stand-alone RO process in brackish water desalination, such as lower hydraulic pressure, less flux decline caused by membrane fouling and higher flux recovery after cleaning. Other benefits in brackish water desalination like no pre-treatment requirement, -1 Flux recovery after cleaning 0.8 Permeate TDS (mgL ) Flux decline 0.9 Normalized Flux -2 -1 -1 Specific Water Flux (Lm h bar ) Brackish water, NF270, 8.5bar 0.06M Na 2SO 4, NF270, 8.5bar Brackish water, BW30LE, 30bar 1000 1200 1400 1600 Time (min) Fig. 7. Comparison of permeate quality using different membranes for desalting brackish water and the diluted Na2SO4 draw solution.