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Table 6.2 :
Comparison of minimum sticking efficiencies ( mi Α ) obtained from this study
(left two columns) and from Lutterodt et al. (2009b, 2011; Chapters 4 and 5 )
Strain
Strain
Α
min ( )
Α
min ( )
(Lutterodt et al.,
2009b)
Α
min ( )
(Lutterodt et al.,
2011)
SL03
1.34x10 -5
UCFL-71
4.70x10 -2
1.72x10 -4
6.06x10 -6
1.68x10 -7
FR08
UCFL-94
1.83x10 -4
9.44x10 -3
6.75x10 -8
FR02
UCFL-131
8.13x10 -5
1.73x10 -1
FA03
UCFL-167
4.72x10 -5
3.39x10 -2
SL20
UCFL-263
~0.1
FR05
UCFL-348
≥1
6.5 Discussion
From our experiments we concluded that the segment sticking efficiency, Α, was not a
constant, but reduced with increasing transport distance. Furthermore, power law distribution
functions were capable of adequately describing the relation between
F
and
Α, and
minimum sticking efficiencies (
Α
), calculated from these power law distribution functions
min
usually ranged from 10 -5 to 10 -4 .
6.5.1 Attachment variation within and among bacteria strains
Our observation that the six E. coli strains revealed variation in their interaction with quartz
sand, as witnessed by the varying segment sticking efficiencies, Α, is consistent with
observations made for E. coli strains isolated from different sources (Schinner et al., 2010,
Bolster et al., 2009, Bolster et al., 2006, Lutterodt et al., 2011, 2009b). Such reductions in Α
with increasing transport distance have been explained in literature (Lutterodt et al., 2009a,
2009b, 2011; Chapters 2 , 4 and 5 of this thesis; Tufenkji and Elimelech, 2005b, 2004b;
Simoni et al., 1998; Baygents et al., 1998) by heterogeneity in cell surface characteristics.
Many workers have attributed higher sticking efficiencies obtained at transport distances near
influent end of a column to preferential removal of cells with characteristics that promote
their attachment to collector surfaces (Foppen et al., 2007a, 2007b; Bolster et al., 1999, 2000;
Li et al., 2004). The low aspect ratio between the average collector grain size and average
size of the strain used enabled us to rule out the possibility of straining (see Methods
Section). The observed Α variations of 1.1 log-unit within the E. coli strains are consistent
with our previous work, despite the fact that growth conditions of the E. coli strains applied
in the two studies differed. We can conclude from this that for E. coli strains isolated from
different sources, though the magnitude of cell attachment differed; the transport behavior
was similar with respect to intra-strain attachment variations.
 
 
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