TECHNOLOGY
| 30 | Desalination & Water Reuse | May-June 2014
The obtained MFI value is corrected
for temperature and pressure and shows
a linear relation with colloidal/suspended
matter concentration (Figure 4, page 29).
Predicting the rate of fouling in RO
systems based on the MFI-0.45 is possible,
assuming that cake/gel filtration is the
dominant mechanism. However, the
predicted rate of fouling turns out to be
very low for an MFI of 1 s/L
2
, (equivalent
to SDI
15
1 to 3). A pressure increase of
1 bar is predicted to occur in more than
100 years with RO feedwater with an MFI-
0.45 = 1 s/L
2
. This calculation is based
upon equation 2 (see
9-11
for its derivation).
TECHNOLOGY
Figure 5: Scanning electron micrograph of the
MFI-UF PAN 13 kDa membrane showing pore size
comparison to MFI-0.45 membrane pore
(× 100,000 magnification)
12
.
Figure 6: MFI-UF (PAN 13 kDa) as a function of pressure for different sources
13
Figure 7: Filtration set-up to measure MF-UF at constant flux
10
Figure 8: MFI-UF (PES, 10 kDa and 100 kDa) of seawater as a function of flux
10,11
Figure 9: "Safe MFI" as a function of deposition factor and flux
10
Equa on 2
MOdifiEd fOuLiNG iNdEx –
uLTrafiLTraTiON (Mfi-uf)
Based on the above, it was concluded that
particles much smaller than 0.45 µm were
MFI-UF,
s/L
2
MFI,
s/L
2
Deposi on factor (Ω )
Safe MFI value based in
1 bar increase in 6 months
J=10 L/m2-h
J=20 L/m2-h
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
5,000
4,000
3,000
2,000
1,000
0
Flux, L/m
2
h
0.0 50 100 150 200 250 300 350 400
25,000
20,000
15,000
10,00
5,000
0
10 kDa
100 kDa
