Investigating the performance of ammonium sulphate draw solution in fertilizer drawn forward osmosis process

This work investigated the performance of ammonium sulphate as a draw solution in a fertilizer drawn forward osmosis (FDFO) desalination process using thin-film composite (TFC) membrane. Performance has been assessed by the water flux, reverse permeation and the forward rejection of the feed solutes. A logarithmic relation has been determined between flux and ammonium sulphate concentration. As water flux increased, the specific reverse solute flux (SRSF) of NH4+ and SO42− ions dropped, which is a favourable condition. Reverse permeation values obtained at flux less than 10 L/m2/h are significantly higher than that for flux more than 10 L/m2/h. Thus, it is recommended to operate the process at a flux higher than 10 L/m2/h to avoid loss of draw solute by reverse permeation. SRSF was almost constant irrespective of ammonium sulphate concentration. TFC membrane used in this study exhibited high rejection of feed solution ions for almost all draw solution concentrations except when operated at low ammonium sulphate concentration and high feed solution concentration. In conclusion, ammonium sulphate is an efficient draw solution for FDFO process when run at water flux more than 10 L/m2/h exhibiting high osmotic pressure, low reverse solute permeation and high rejection of feed solute.