Seawater desalination: nanofiltration—a substitute for reverse osmosis?

Abstract

We present the possibility to replace the first-stage reverse osmosis (RO) seawater by nanofiltration (NF) membranes. Then, we tested few membranes in the laboratory (NF200, NF2540, MPS44, and MPS34) on synthetic and natural seawater, for 2.6 m² membrane area pilot. We observed that the membrane NF200 is the best membrane from all tested due to its higher productivity with 1.8 L h⁻¹ m⁻² bar⁻¹ and its higher salt rejection with 60%. Furthermore, as expected, NF200 filtration of natural seawater permits to decrease SDI₃ to a value of 4 ± 2%/min and total organic carbon under 0.1 mg/L, eliminating totally the risk of biofouling development on second-stage RO treatment. The configuration NF200-SW30 gave the best energy gain with 29%. The permeate obtained presents a total dissolved solids of 324 ppm and the flow yield ratio increase of 16%, in reference to SW30-SW30 configuration. Also, we tested the limits of ROSA^TM simulation, especially for NF membranes. We observed lots of flaws, especially for high pressures and high salts concentrations. As a consequence, each simulation realized for NF must be validated by experiments on real seawater to a sufficient scale and during sufficient time of experiments.

Keywords:

• Membrane
• Reverse osmosis
• Nanofiltration
• Mass transfer modeling
• Simulation
• Pretreatment
• Seawater

Notes

Presented at the International Conference on Desalination for the Environment, Clean Water and Energy, European Desalination Society, 23–26 April 2012, Barcelona, Spain