(430f) A Molecular Marker Approach for Characterization of RO Membranes and Solute Transport in Spiral-Wound RO Membrane Systems

Over the last few decades, there has been a marked growth in the application and integration of reverse osmosis (RO) with conventional processes for water production. RO processes are now used not only for seawater and brackish water desalination, but are also finding use in agricultural drainage water desalting, nitrate and color removal from impaired groundwater, as well as in water reuse applications. Even though RO is effective in rejecting solutes as small as monovalent ions, there are factors that may impact membrane performance (e.g. flux and rejection). These include membrane fouling and mineral scaling due to concentration polarization, inadequate hydrodynamic mixing in membrane modules, as well as loss of membrane integrity (e.g., due to prolonged exposure to disinfectants such as chlorine, as well as physical damage caused by manufacturing defects, faulty installation and maintenance, failure of components, and stress and strain on membrane surface from operating condition). In order to ensure robust process performance, it is paramount to obtain real-time information on solute transport parameters, hydrodynamics conditions, and membrane integrity. Accordingly, in the present study, an online fluorescent marker-based approach was developed for spiral-wound RO membrane systems for real-time monitoring of: (a) membrane mass transfer coefficient on the feed-side channel which enables assessment of concentration polarization conditions; (b) solute residence time distribution which provides information regarding hydrodynamic conditions in membrane modules and thus inference regarding potential structural changes within membrane elements, as well as membrane fouling and mineral scaling; and (c) transport parameters (e.g., solute solution-diffusion transport parameter and reflection coefficient) that enable characterization of membrane integrity. The approach involved a controlled introduction of a fluorescent marker dose to the feed stream and online monitoring of the marker concentration in the permeate and concentrate streams. Experimental studies were carried out, with an especially-designed online fluorescent marker detection system, using both intact and compromised (by exposure to chlorine and via mechanically induced damage). Results from the present study demonstrated the technical feasibility for real-time online assessment of concentration polarization, marker transport parameters, and highly sensitive detection of membrane integrity in spiral-wound RO membrane systems.