Forward osmosis (FO) is a promising technology for efficient water reclamation at low operating costs. It has shown potential in producing fresh water from seawater; however, the regeneration of the diluted draw solution (DS) still holds back further development. Thermo-responsive polymers, especially polyalkylene glycol (PAG) based copolymers with hydrophilic ethylene oxide and hydrophobic propylene oxide units, have shown suitability as DSs in FO using low-temperature waste heat to regenerate the DS. In this study, we explored five commercially available copolymers: Pluronic® PE 6400, Pluronic® L-35, Pluronic® RPE 1740, Unilube® 50 MB-26, and Polycerin® 55GI-2601 as DSs in a laboratory FO setup, with DI water as the feed solution (FS). The water
flux and reverse solute flux varied from 1.5 to 2.0 L⋅m􀀀 2⋅h􀀀 1 and from 0.04 to 0.4 g⋅m􀀀 2⋅h􀀀 1, respectively.

Furthermore, all polymer solutions showed the ability to be recovered and reused using temperatures below 100◦C. Therefore, the tested PAGs turned out to be promising as draw solutions for FO systems that utilize low-grade waste heat. The re-usage in FO was shown for regenerated Pluronic® L-35 through a three-step experiment where its recovery was 91.1 %, 93.1 %, and 91.9 % for each FO cycle, respectively.

Keywords: Forward osmosis, Draw solution, Osmotic pressure, Polyalkylene glycols, Lower critical, solution temperature, Reuse of polymer.

Authors: Irena Petrinic, Natalija Jancic, Ross D. Jansen van Vuuren, and Hermina Buksek.