Desalination process using super hydrophilic nanoparticles via forward osmosis integrated with ultrafiltration regeneration

For the first time, a potentially sustainable integrated FO–UF (forward osmosis–ultrafiltration) system for water reuse and desalination with the aid of super hydrophilic nanoparticles as draw solutes has been proposed. The system uses an FO membrane as the semi-permeable membrane to reject salts, super hydrophilic nanoparticles as draw solutes to induce water across the FO membrane, and UF membranes to regenerate the draw solutes. For comparison, a magnetic separator was also used to recycle super hydrophilic magnetic nanoparticles but agglomeration was observed. Ultrasonication proved to effectively reduce the size of agglomerated magnetic nanoparticle and the FO performance was partially restored. However, the resultant magnetic properties were weakened under ultrasonic processes and thus jeopardized regeneration efficiency in magnetic fields. The novel FO–UF process was tested for 5 continuous runs for the purpose of desalination without increasing nanoparticle draw solute size or reducing osmotic functionality. UF membranes of small pore diameter and narrow pore size distribution can enhance the recovery efficiency of nanoparticle draw solution. The proposed FO–UF integrated system using super hydrophilic nanoparticles as draw solutes is believed to be a promising technology to desalinate both seawater and brackish water and to reclaim water from wastewater.

Highlights
► A FO–UF system using hydrophilic nanoparticles as draw solute was demonstrated.
► PAA-NPs draw solution can be recycled in FO-UF 5 times for desalination.
► Proper UF membranes can improve recovery efficiency of nanoparticle draw solution.