Energy-efficient desalination by forward osmosis using responsive ionic liquid draw solutes

Abstract

We demonstrate a class of thermally responsive ionic liquids (ILs) as novel draw solutes for forward osmosis (FO) seawater desalination with electrical energy consumption significantly lower than that of seawater reverse osmosis (RO). These draw solutes can draw water from feed solutions of up to 1.6 M NaCl and hence have potential to treat high salinity feed streams including RO brine. Draw solution regeneration can be achieved energy-efficiently via a thermally stimulated phase separation process using less expensive low grade heat in combination with electrically driven nanofiltration. The electrical energy consumption is estimated to be as low as 16% of that needed for the state-of-the-art RO desalination leading to significant reduction of energy cost and carbon footprint.