(539e) A Molecular Marker Approach for Real-Time Characterization of RO Membrane Integrity

The use of reverse osmosis (RO) processes has grown significantly over the past few decades in water treatment and reuse applications to safeguard water supplies against harmful pathogens and impurities, as well as reducing water salinity to enable indirect potable water reuse. Maintaining membrane transport characteristics (e.g., flux and rejection) are paramount to ensuring process performance, particularly with respect to the passage of organics and nanosize enteric viruses that may pose a potential health hazard. Loss of membrane integrity (e.g., due to exposure to oxidants such as chlorine) is of particular concern in water reuse applications where passage of nano-size contaminants (e.g., enteric viruses) can occur due to membrane integrity breaches. Accordingly, given the need for online membrane performance monitoring, an online fluorescent marker-based approach was developed for membrane integrity detection and characterization. The approach involves dosing the feed stream with a molecular marker and monitoring its concentration in the permeate and concentrate streams. The change in marker concentration in response to a controlled marker dose to the feed is then monitored online. Application of the relevant membrane solute flux model, along with analysis of the marker’s residence time distribution, then enables assessment of the detection of membrane integrity breaches, given previous characterization of the membrane with respect to the marker permeability. In the present study, detection and quantification of the effect of membrane breaches (induced by controlled exposure to sodium hypochlorite) on membrane transport characteristics was evaluated for commercial polyamide RO membranes. Membrane integrity breaches were first characterized by imaging via scanning electron microscope (SEM) and atomic force microscope (AFM) imaging. The characteristics of integrity breach were then correlated with the level and mode of chlorine exposure. Subsequently, experimental studies were carried out, with a specially-designed online fluorescent marker detection system, using both flat-sheet membranes (in a plate-and-frame RO cell) as well as in a spiral-wound membrane pilot. Results from the study demonstrated the technical feasibility for real-time online characterization of RO membrane integrity breaches as well as assessment of RO module performance.