Hybrid Ion Exchange Desalination (HIX-Desal) of Impaired Brackish Water Using Pressurized Carbon Dioxide (CO2) as the Source of Energy and Regenerant

Reverse osmosis and electrodialysis are truly the only water desalination processes currently in practice for the entire range of total dissolved solids (TDS) from 400-40,000 mg/L. For high recovery of 80% or more, membrane processes are energy intensive even for a feedwater with a TDS of 1000 mg/L and demand significant pretreatment to avoid precipitation and consequent membrane fouling. In this study, we present for the first time a hybrid ion exchange desalination (HAIX-Desal) process that does not require any semipermeable membrane and can desalinate lean brackish water (TDS <= 1500 mg/L) using CO2 as the sole source of energy and chemical regenerant. A hybrid anion exchanger with dispersed ZrO2 nanoparticles (HAIX-NanoZr) and a shell core weak-acid cation exchange (SC-WAC) resin form the heart of the process. Carbon dioxide or CO2 at 10 atm pressure is the only chemical needed to sustain the process. In contrast to a conventional deionization plant, the anion exchanger, i.e., HAIX-NanoZr, precedes the cation exchanger or SC-WAC to take advantage of the unique carbonate chemistry for desalination. CO2 serves concurrently as both an acid (i.e., H2CO3) and a base (HCO3-) for the HIX-Desal process. Municipal secondary wastewater (Bethlehem, PA) and synthetic brackish water were used in the experimental study to validate the basic premise of the process.