(255e) Role of Ion Exchange Fundamentals In Membrane Processes

Scientific principles governing pressure-driven reverse osmosis (RO) membrane processes and ion exchange (IX) separation processes are seemingly different; equipment configurations and operational protocols are also quite dissimilar. RO is essentially a non-selective process for separation of electrolytes from water. However, different ions, even with identical valences, get rejected to a different degree during RO processes under similar operating conditions. For environmentally regulated ions (e.g., nitrate, bromide, perchlorate, barium), such rejections (or salt passages) are important for compliance with statutory regulations. Our research shows that readily available ion exchange selectivity can be used as surrogate indicators to predict the relative permeability of different ions through RO and NF membranes. Also, potential precipitation of calcium and barium sulfates at the RO membrane interface caused by concentration polarization is a problem that disallows higher water recovery and requires continuous dosing of anti-scaling agent. By appropriately introducing a reversible IX process that is self-regenerating, the membrane fouling caused by sulfate salts can be eliminated altogether. Experimental results and supporting data will be presented.