Freshwater production by solar desalination of seawater using two-ply dye modified membrane system

Freshwater production from seawater using solar energy is now an essential technology as a countermeasure of global water shortage. We have previously reported a seawater desalination process by membrane permeation of the water. In this process, seawater put on dye modified hydrophobic membrane is vaporized by irradiated light with the modified dyes. The water vapor thus formed penetrates through the membrane, and desalinated water is recovered under the membrane. This paper reports our latest approaches to enhance the performance of the solar desalination of seawater by the membrane permeation. Solvent black 5 (SB5) that absorbs the wide range of sunlight including near-infrared light was effective as a dye used for the desalination process. For scaling-up this process, dye modified membranes were tightly sandwiched between two flanges for holding a large volume of seawater on the membrane. The two-ply membrane system consisting of SB5 modified cellulose membrane on non-modified polytetrafluoroethylene membrane was found to be the best combination for freshwater production from seawater by the irradiation of simulated sunlight. Desalination of actual seawater using natural sunlight was also achieved by the two-ply membrane system. These results indicated that the freshwater production by the solar desalination of seawater with the membrane permeation is a practical countermeasure for global water shortage.