The MBR Book: Principles and Applications of Membrane

Fouling relative distribution (%)
100
80
60
40
20
0
[Bae and Tak, 2005]
[Grelier et al., 2005] (1)
[Jang et al., 2005b] (3)
[Grelier et al., 2005] (2)
Suspended solids Colloid Soluble
[Li et al., 2005b] (4)
[Itonaga et al., 2004] MBR
[Lee et al., 2003] (5)
[Itonaga et al., 2004] Hybrid MBR
Colloid
�
Soluble
[Lee et al., 2001a]
[Lee et al., 2003] (6)
[Defrance et al., 2000]
[Bouhabila et al., 2001]
Fundamentals 73
[Wisniewski and Grasmick, 1998]
Figure 2.28 Relative contributions (in %) of the different biomass fractions to MBR fouling
(1–2): For SRT increase from 8(1) to 40 days (2)
(3): F:M ratio of 0.5, results based on modified fouling index
(4): Based on flux reduction after 600 min of each fraction filtration
(5–6): For SRT increase from 20 (5) to 60 days (6).
less than that of the supernatant. The latter is generally regarded as comprising soluble
microbial product (SMP), which is soluble and colloidal matter that derives
from the biomass (Section 2.3.6.5). With respect to fouling mechanisms, soluble and
colloidal materials are assumed to be responsible for membrane pore blockage, whilst
suspended solids account mainly for the cake layer resistance (Itonaga et al., 2004).
However, since iMBRs are typically operated at a modest flux, the cake tends not to
form and deposition of physically smaller species is more likely to take place.
2.3.6.3 Biomass (bulk) parameters
MLSS concentration Whilst suspended solids concentration may seem intuitively to
provide a reasonable indication of fouling propensity, the relationship between
MLSS level and fouling propensity is rather complex. If other biomass characteristics
are ignored, the impact of increasing MLSS on membrane permeability can be either
negative (Chang and Kim, 2005; Cicek et al., 1999), positive (Defrance and Jaffrin,
1999; Le-Clech et al., 2003c), or insignificant (Hong et al., 2002; Lesjean et al.,
2005), as indicated in Table 2.9. The existence of a threshold above which the MLSS