The MBR Book: Principles and Applications of Membrane

Table 2.11 Concentration of SMP components (in mg/L and *mg/gSS)
SMPp SMPc Other Operating conditions Reference
Fundamentals 81
8 25 Humic substance: 36 R, (10) Cabassud et al. (2004)
TOC: Up to 8 mg/L S, (�) Gao et al. (2004b)
0.5–9* n.d. –10* 4–37* (TOC) Four pilot-scale Brookes et al. (2003b)
plants, Municipal
0.5–1* n.d. 11* Three full-scale
plants, Municipal
0.5* n.d. 1.5* Full-scale plant,
Industrial
TOC: 30–70 mg/L S, (�), MLSS 15 g/L Liu et al. (2005)
23 7 R, (not available) Evenblij and van der
Graaf (2004)
DOC: 5 mg/L S, (20) Shin and Kang, 2003
TOC: 8–10 mg/L R, (21) Tao et al. (2005)
10–34 5–33 R, (from 40 to 8) Grelier et al., (2005)
4.5–6 4.5–3.7 S, (20) Ji and Zhou (2006)
n.d.: Non detected; S: Synthetic wastewater; R: Real wastewater; SRT are given in days in bracket,
�: infinite SRT (i.e. no wastage).
characterisation pertaining to flocculation, settling and dewatering in conventional
ASP technologies (Liu and Fang, 2003; Yin et al., 2004) may therefore be germane
to MBR technologies.
Since the EPS matrix features in floc formation (Liu and Fang, 2003) and specifically
the hydrophobic interactions between microbial cells, a decrease in EPS levels
may be expected to cause floc deterioration, as indicated by the results from a comparative
study of nitrification/denitrification in an MBR (Jang et al., 2005a). This
would seem to imply that too low an EPS level is detrimental to MBR performance,
though there is no firm experimental evidence to prove this.
Many operating parameters including gas sparging, substrate composition
(Fawehinmi et al., 2004) and OLR (Cha et al., 2004; Ng et al., 2005) appear to affect EPS
characteristics in the MBR, but SRT is probably the most significant (Hernandez Rojas
et al., 2005). A decrease in EPS levels has been observed for extended SRTs, with this
reduction becoming negligible at SRTs greater than 30 days (Brookes et al., 2003b).
Lee and co-workers (Lee et al., 2003) observed an increase in protein concentration
(along with stable carbohydrate levels) when SRT was increased.
Soluble microbial products Whilst the impact of dissolved matter on fouling has been
studied for over a decade, the concept of SMP fouling in the MBR is a relatively new
one (Chang et al., 2002a), with available data being reported within the last few
years (Table 2.11). Experiments recently conducted with a dual compartment MBR,
where the membrane was challenged ostensibly with the mixed liquor supernatant
(i.e. the SMP) rather than the whole biomass (Ng et al., 2005), have revealed greater filtration
resistance from the SMP than from the biomass at 4 g/L MLSS concentration.
This implies that SMP characteristics have a significant impact on membrane permeability.
During filtration, SMP materials are thought to adsorb onto the membrane
surface, block membrane pores and/or form a gel structure on the membrane