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Membrane Filtration Regulations and Determination of Log Removal Value 161
Table 4.5
Example challenge test solution volume for various types of modules
Module Example
membrane area
[ft 2 (m 2 )]
Example
maximum flux
[gal/ft 2 /d
(L/m 2 /h)]
Test
duration
(min)
Recovery
(%)
Volume (V test)
[gal (L)]
Cartridge filter 5 (0.46) 1,364 (2,316) 30 100 155 (586)
Spiral-wound 4" diameter 75 (7.0) 17.8 (30.2) 30 85 36.1 (137)
8" diameter 350 (32.5) 17.8 (30.2) 30 85 168 (635)
Hollow-fiber Outside-in 350 (32.5) 53.5 (90.8) 30 100 429 (1623)
Inside-out 1,400 (130) 107 (182) 30 100 3,438 (13,013)
The duration of the challenge test, Tmin as given in Eq. (3), does not include the time
required for the test solution to come to equilibrium, as this is taken into account by the
parameter Veq. Thus, Tmin represents the time necessary to implement the sampling program
associated with the challenge test, which typically requires less than 1 h.
Table 4.5 provides examples of the challenge test solution volumes (i.e., Vtest) required as
calculated using Eq. (3) for various membrane configurations under the listed conditions, in
these cases assuming the system hold-up volume (Vhold) and volume required to achieve
equilibrium (Veq) are negligible and a safety factor of 1.1. The filtrate flow (Qp) is not shown
specifically in the table but is calculated simply by multiplying the membrane area and
maximum flux. Table 4.5 is intended to be illustrative only. Thus, it is recommended that the
solution volume requirements for a specific challenge test be determined according to
the procedure described above. Also, note that the values listed in Table 4.5 are examples
only and that particular product specifications will vary by module manufacturer.
4.8.3. Test Solution Concentration
The concentration of the test solution is based on the target LRV to be demonstrated during
the challenge test (LRVt) and the detection limit for the challenge particulate in the filtrate
samples. Since challenge testing is intended to be a one-time, product-specific requirement,
it is generally advantageous to select a LRVt at or near the maximum of 6.5 log removal that
can be demonstrated under the LT2ESWTR. The detection limit is a function of the analytical
technique used to enumerate the challenge particulate and the filtrate sample volume. For
example, if the method can detect 1 particle in a sample, and the filtrate sample volume is 1 L,
the detection limit is 1 particle/L. The detection limit and maximum 6.5 LRV are used
to calculate the maximum feed concentration that can be used during a challenge test, as
shown in Eq. (4)
Cf max ¼ 3:16 10 6 DL; (4Þ
where Cf-max is the maximum feed concentration, number or mass/volume, DL is the
detection limit in the filtrate, number or mass/volume.