Evaluation of hydroacid complex in the forward osmosis–membrane distillation (FO–MD) system for desalination

Abstract The incorporation of membrane distillation (MD) into forward osmosis (FO) provides process sustainability to regenerate the draw solution and to produce clean water simultaneously. However, the reverse salt flux is the major hurdle in the FO–MD system because it not only reduces the effective osmotic driving force across the membrane but also increases the replenishment cost and scaling issue. For the first time, a hydroacid complex with abundant hydrophilic groups and ionic species is evaluated as the draw solutes in the hybrid FO–MD system consisting of multi-bore PVDF MD membranes for seawater/brackish desalination. In order to evaluate the practicality of the hydroacid complex in the FO–MD system, FO and MD experiments were conducted at elevated temperatures and concentrations. The hydroacid complex has displayed desired properties such as high solubility, low viscosity, excellent thermal stability and minimal reverse salt flux suitable for FO and MD operations. FO–MD desalination process was demonstrated with a highest seawater desalination flux of 6/32 LMH (FO/MD). This study may open up the prospective of employing the hydroacid complex as the draw solute in FO–MD hybrid systems for seawater /brackish desalination.