Zinc sulfate as a draw solute in forward osmosis and its regeneration by reagent precipitation

Abstract

Forward osmosis (FO) is an emerging membrane technology that has gained huge interest for water treatment and reclamation, owing to its low energy consumption. Nevertheless, the lack of ideal draw solutions and efficient membranes hinder its large-scale applications. In this study, the potential of zinc sulfate draw solute to recover water from different brackish waters by FO was evaluated in terms of permeate water flux, reverse solute flux, and rate of water recovery. Product water having 9.8 and 360 ppm of total dissolved solids (TDS) was recovered from the diluted draw solution by employing a reagent precipitation (RP) and nanofiltration (NF) process, respectively. The draw solution was regenerated by adding a stoichiometric amount of sulfuric acid to the precipitates obtained in RP. In addition, the specific energy consumption (SEC) and water production cost for the water desalination using an FO-RP process were calculated and compared to the FO-NF and a stand-alone RO process. The SEC and water production cost for the FO-RP process were found to be about 0.5 kWh·m−3 and 0.09 $·m−3, respectively. Finally, it is suggested that zinc sulfate could be an excellent choice as a draw solute for water desalination by FO when coupled with reagent precipitation.