Novel draw solutes of iron complexes easier recovery in forward osmosis process

Forward osmotic (FO) membrane is a new process for producing fresh water from salt water. The study of draw solute is essential in the development and application of FO technology; draw solution should be good at drawing water and easy at recovery. In this paper, three complex draw solutes such as ammonium iron (II) sulfate, ammonium iron (III) sulfate and ammonium iron (III) citrate with different concentrations were studied. The physical properties such as pH, conductivity and total dissolved solids (TDS) have simultaneously been investigated. The pH of most ammonium complexes was decreased whereas TDS increased with increasing of draw solution concentrations. We found that high water flux of these iron complexes was reported in the range of 8.88–11.24 LMH which was higher than the ammonium bicarbonate draw solution. In addition, more than 90% iron complexes draw solutions were recovered by NF-90 membrane, which plays an important role in the FO process to produce fresh water. This study provides direct evidence for the ability of permeate water from feed solution to draw solution, which shows the potential applications of iron complexes in FO process to produce fresh water from sea-, brackish or river water.