(148a) Hybrid Ion Exchange/nanofiltration (Hix-Nf) for Energy Efficient Desalination of Brackish and Sea Water

According to the Desalination and Water Purification Technology Roadmap (DWPTR) from the US Department of the interior, the cost-effectiveness of the reverse osmosis (RO) process for the desalination of brackish or sea water is adversely affected by high energy consumption and membrane fouling. To this end, we have conceived a new hybrid ion exchange/nanofiltration (HIX-NF) process at Lehigh University and carried out laboratory experiments under representative conditions. The HIX-NF process considerably reduces energy consumption for desalination and replaces RO with nanofiltration (NF) membranes that are less susceptible to fouling. The HIX-NF process rests on the three following scientific tenets: 1. Ion exchange processes work on equivalents (normality) of ions while the osmotic pressure of an aqueous solution is governed by molar concentrations of ions. 2. At higher ionic strength, polymeric ion exchange resins tend to offer identical selectivity for monovalent and divalent ions. 3. At the identical feed electrolyte concentrations with divalent ions, nanofiltration membranes offer significantly greater water flux with equally high salt rejection compared to RO membranes at identical transmembrane pressure. Sufficient laboratory data will be presented to validate the energy efficiency of the HIX-NF compared to traditional RO processes. Also, the challenges for lage-scale deployment of the the hybrid process will be emphasized.