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Measurement of Normalized
Water Permeability (NWP)
The normalized water permeability (NWP) for Pellicon
®
Cassette
membranes should be established prior to the first use of each
filter. New membranes should be cleaned, flushed, and integrity
tested before measuring NWP. The NWP measured at this point is
used as a benchmark against subsequent NWP measurements to
determine cleaning efficacy.
1. Direct the permeate and retentate lines to the drain. Close
the tank drain valve and open the retentate valve. Open the
permeate valve if present.
2. Fill the tank with filtered deionized water, water for injection, or
reverse osmosis water. The flush water must be extremely pure to
avoid fouling the membranes or introducing other contaminants
into the system. The NWP may be measured with solutions other
than water (i.e., storage solution or buffer) as long as the same
conditions and solution are used for each measurement.
3. Turn on the feed pump and pump water into the feed port of
the Pellicon
®
holder at a flow rate of 1–4 L/min/m
2
.
4. When flow is established, partially close the retentate valve, if
necessary, to achieve a conversion of approximately 30–90%.
The same feed flow rate and pressure conditions MUST be used
each time NWP is measured to ensure accuracy.
5. Flush water for a minimum of ten minutes. Ensure that the
pressure and the temperature conditions are stable.
6. Record the feed and permeate flow rates, feed, retentate, and
permeate pressures, and the temperature of the water.
7. After the NWP measurement is complete, continue pumping
until the flow path lines are drained.
NOTE: NWP measurement for individual sections:
For Pellicon
®
2 0.1 m² and Pellicon
®
3 88 cm² and 0.11 m²
cassette installations, NWP can be measured for the
individual cassettes with all other cassettes installed in the
holder with diverter plates by measuring the pressures and
permeate flows of each section independently.
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