The MBR Book: Principles and Applications of Membrane

Table 2.6 Effect of pore size on MBR hydraulic performances
Membranes tested Optimum Test duration Other Reference
Fundamentals 65
0.1, 0.22, 0.45 �m 0.22 �m 20 h – Zhang et al. (2006)
20, 30, 50, 70 kDa 70 kDa 110 min Concentrated He et al. (2005)
50 kDa 110 days feed, anaerobic
70 kDa, 0.3 �m 70 kDa 8 h – Choi et al. (2005a)
30 kDa, 0.3 �m 30 kDa 2 h CFV � 0.1 m/s Choi et al. (2005b)
0.3 �m CFV � 3.5 m/s
0.1, 0.2, 0.4, 0.8 �m 0.8�m n/a – Lee et al. (2005)
200 kDa, 0.1, 1 �m 1�m 3 h Flux-step test Le-Clech et al. (2003c)
0.3, 1.5, 3, 5 �m 5�m 25 min – Chang et al. (2001b)
0.3 �m 45 days
0.4, 5 �m 0.4�m 1 day – Gander et al. (2000)
No effect From 50 days
0.01, 0.2, 1 �m No effect A few hours Flux-step test Madaeni et al. (1999)
200 kDa, 0.1, 1 �m 0.1�m n/a Anaerobic Choo and Lee (1996a)
0.05, 0.4 �m 0.05 �m n/a – Chang et al. (1994)
separation. The pore size of commercial MBR materials tends to be in the coarse UF
to fine MF region (Section 4.7), since experience indicates that this pore size range
offers sufficient rejection and reasonable fouling control under the conditions
employed. The range of organic membrane materials employed is also, in practice,
limited to those polymers which are:
(a) sufficiently mechanically and chemically robust to withstand the stresses
imposed during the filtration and cleaning cycles,
(b) readily modified to provide a hydrophilic surface, which then makes them
more resistant to fouling, particularly by EPS (Section 2.3.6.5),
(c) readily attached to a substrate to provide the mechanical integrity required, and
(d) manufactured at a relatively low cost.
Point (d) is especially important in the case of iMBRs, since these operate at relatively
low fluxes and so demand much larger membrane areas than sMBRs.
2.3.5.1 Physical parameters
Pore size The effects of pore size on membrane fouling are strongly related to the
feed solution characteristics and, in particular, the particle size distribution (Section
2.3.6.1). This has led to conflicting trends reported in the literature (Table 2.6), with
no consistent general trend noted between pore size and hydraulic performance.
This can, in part, be attributed to the complex and changing nature of the biological
suspension in MBR systems and the comparatively large pore size distribution the
membranes used (Chang et al., 2002a; Le-Clech et al., 2003c), along with operational
facets such as the system hydrodynamics and the duration of the test. A direct
comparison of MF and UF membranes at a CFV of 0.1 m/s has shown an MF membrane