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4.5.1 Remove Air from Cassette and System
Caution: It is important to completely remove air from the feed channels to wet out
the membrane before determining NWP20 °C. Both permeate ports should be open
for determining NWP20 °C. Closing one port can cause a significant error in TMP
measurement due to internal pressure drops.
Direct the retentate and permeate lines back to the feed tank to minimize the volume
of water needed.
Figure 20
System Setup for Determining Membrane Water Permeability
Procedure
1. Check the water level in the feed tank and refill if necessary.
2. Open the permeate and retentate valve completely.
3. Adjust the pump speed to deliver the recommended cross flow flux. Refer to
Table 3.
(i) If required, set the pump flow rate to the required retentate flow rate.
(ii) Adjust the permeate valve till retentate and permeate flow rates are
approximately equal.
(iii) Readjust the pump speed to deliver the required retentate flow rate.
4. Close the retentate valve till the feed pressure increases by 0.7 to 1 barg
(10 to 15 psig) or the valve is completely closed, then open immediately.
Caution: Do not exceed a feed pressure of 3 barg (45 psig).
5. Repeat previous step at least three times to remove air.
4.5.2 Determine Initial Water Permeability (Dead-end Method)
Procedure
1. Close the retentate valve and open the permeate valve.
2. Adjust the feed pump flow rate to generate the desired transmembrane pressure
(TMP). Start at the lowest TMP.
Retentate
Permeate
Feed
Tank
Feed
Pump
Rp
Pp
Fp
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