(279g) Integrating Tunable Anion Exchange with Reverse Osmosis for Inland Brackish Water Desalination

Ion Exchange (IX) and Reverse Osmosis (RO) are universally recognized as two fundamentally different processes for treating water. While RO uses semi-permeable membranes to separate dissolved electrolytes from water, IX uses functionalized polymeric materials, mostly in the form of beads or granules, to remove dissolved ions from water. Although seemingly unrelated, we present here the results of an investigation that acts as a bridge between the RO and IX processes to mitigate the problems associated with brackish water desalination. Most brackish water desalination plants are located inland and must resort to expensive concentrate disposal methods like deep well injection or evaporation ponds. Increasing the recovery of RO process would obviously reduce the volume of concentrate to be disposed of but cannot be implemented due to scaling of sulfate salts (CaSO₄, BaSO₄, etc.) and consequent fouling of RO membranes. Similar fouling is likely to occur in the presence of phosphate and aggravated by concentration polarization at the membrane-water interface. We have developed a hybrid Ione Exchange-Reverse Osmosis (HIX-RO) process where tunable anion exchange resins can eliminate sulfate precipitation without addition of external regenerants or anti-scaling chemicals. At the same time permeate recovery is enhanced and the volume of the concentrate can be cut in half or even lower. Results of the experimental study from a five-year long investigation will be presented.