Microbial Removal and Integrity Monitoring of High-Pressure Membranes

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High-pressure (HP) membranes, reverse osmosis, and nanofiltration are used increasingly to treat brackish and organic laden surface waters as water purveyors are forced to utilize lower quality source waters to meet potable water demands. In addition, reverse osmosis has become an integral part of the advanced reclamation process for the indirect potable reuse of domestic wastewaters. In these applications, HP membranes are expected to serve as a positive barrier to pathogens. To date, integrity methods for full-scale HP membrane systems have been limited to conductivity and total organic carbon monitoring, approaches that can only assess pathogen removals to two logs (99%). The first objective of this research was to determine the integrity of RO and NF membrane systems with respect to viral passage using both particulate (MS2 viruses and fluorescent microspheres) and soluble (Rhodamine WT) surrogates. The second objective was to compare the capability of these surrogates for use in assessing integrity of intact and compromised RO and NF membranes when evaluated in a number of configurations. Intact (uncompromised) RO membranes, whether in flat-leaf or spiral-wound- element form, demonstrated 6 logs virus removal (MS-2 phage). Intact NF membranes in element form showed lower removals ranging from 3 to 5.5 logs. Good correlations were observed between MS-2 phage and the two non-biologic viral surrogates evaluated, Rhodamine WT and fluorescent microspheres, when used to indicate loss of integrity in spiral wound HP membrane systems when such systems were compromised by inducing imperfections in both membrane sheet and in o-ring connectors. Of the non-biologic surrogate viral integrity methods evaluated, only Rhodamine WT is currently practical for application at full-scale, although as a solute, it's application does have limitations.