The MBR Book: Principles and Applications of Membrane

74 The MBR Book
Table 2.9 Influence of shift in MLSS concentration (g/L) on MBR fouling
MLSS shift Details Reference
(g/L)
Fouling increase
0.09–3.7 Cake resistance: 21–54 1011 /m and
�: 18.5–0.7 10
Chang and Kim (2005)
8 m/kg
2.4–9.6 Total resistance: 9–22 1011 /m Fang and Shi (2005)
7–18 Critical flux: 47–36 LMH (for SRT
of 30–100 days)
Han et al. (2005)
2.1–9.6 Critical flux: 13–8 LMH Bin et al. (2004)
1–10 Critical flux: 75–35 LMH Madaeni et al. (1999)*
2–15 “Limiting flux”: 105–50 LMH Cicek et al. (1998)*
1.6–22
Fouling decrease
“Stabilized flux”: 65–25 LMH Beaubien et al. (1996)*
3.5–10
No (or little) effect
Critical flux: �80, �60 LMH Defrance and Jaffrin (1999)*
4.4–11.6 No impact between 4 and 8 g/L,
Slightly less fouling for 12 g/L
Le-Clech et al. (2003c)
4–15.1 Critical flux decreased from
25 to 22 LMH
Bouhabila et al. (1998)
3.6–8.4 Hong et al. (2002)
*sMBR
concentration has a negative influence has been reported (30 g/L, according to
Lubbecke et al., 1995). A more detailed fouling trend has been described (Rosenberger
et al., 2005), in which an increase in MLSS reduced fouling at low MLSS levels (�6 g/L)
whilst exacerbating fouling at MLSS concentrations above 15 g/L. The level of MLSS
did not appear to have a significant effect on membrane fouling between 8 and 12 g/L.
In another study of MLSS concentration impacts (WERF, 2005), it was concluded that
hydrodynamics (more than MLSS concentration) control the critical flux at MLSS levels
above 5 g/L.
Contradictory trends from data obtained in the same study are apparent. For
example, the cake resistance (R c) has been observed to increase and the specific cake
resistance (�, the resistance per unit cake depth) to decrease with increasing MLSS,
indicating that the bulk cake becomes more permeable. Bin et al. (2004) observed
the permeate flux to decrease (albeit at a reduced fouling rate) with increasing
MLSS. This was attributed to the rapid formation of a fouling cake layer (potentially
protecting the membrane) at high concentration, while progressive pore blocking
created by colloids and particles was thought to take place at lower MLSS concentrations
when the membrane was less well protected. This may well explain the subcritical
fouling behaviour depicted in Fig. 2.14.
Empirical relationships predicting flux from MLSS level have been proposed in
a number of papers (Fang and Shi, 2005; Krauth and Staab, 1993; Sato and Ishii,
1991; Shimizu et al., 1996). However, these equations have limited use as they are
generally obtained under very specific conditions and are based on a limited number
of operating parameters, whilst other parameters are disregarded. A mathematical
expression linking MLSS concentration, EPS and TMP with specific cake resistance