The successful application of high-pressure membrane
processes as effective barriers to pathogens requires the
use of online methods for monitoring and controlling membrane
integrity during process operation. Currently available
integrity monitoring methods involving conductivity and total
organic carbon have a resolution of only ~99% (2 log removal), but
intact nanofiltration (NF) and reverse osmosis (RO) membranes
and systems can provide much greater pathogen removal (>4 logs).
Reliable and cost-effective integrity methods having equivalent
resolution are needed in order for regulatory agencies to permit
(and utilities to realize) the pathogen-removal credits for which
membranes are capable.
This research evaluated two new integrity monitoring methods
that use nonmicrobial viral surrogates, fluorescent microspheres
and fluorescent Rhodamine WT dye (RWT), to measure NF/RO
membrane and system integrity under both intact and compromised
conditions. Microsphere dosing to feedwater demonstrated
viral removal at greater than the target level of 4 logs, but given
the current cost of such microspheres and the required analytical
sophistication, such resolution is only cost-effective at pilot scale.
In contrast, RWT proved a practical full-scale viral surrogate for
RO, and to a lesser extent, NF system integrity. RWT is inexpensive,
easy to dose, and can accurately measure ~4 log removal at
a feed concentration of <2 mg/L.
The study also found that quality assurance/quality control
(QA/QC) measures currently used by manufacturers are insufficient
and that membranes passing normal QA/QC tests vary
widely in their viral removal ability. However, membrane imperfections
that allow significant virus passage can be "healed" through
fouling from normal operation. This operational benefit should be
considered by regulators when granting log-removal credits for
membranes. Includes 13 references, tables, figures.
| Edition : | Vol. 95 - No. 12 |
| File Size : | 1
file
, 200 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 15 |
| Published : | 12/01/2003 |
