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vulnerability of the springs to fecal contamination. The lack of direct correlation between EC
and thermotolerant coliforms suggested the possibility of multiple sources
of fecal pollution
leaching into the aquifers and polluting ground- and springwaters.
Based on the column experiments, an important second conclusion from our work was that
maximum peak relative breakthrough and modeling results revealed an overall transport
homogeneity among the
E. coli
strains: some 82 % of the strains had a maximum relative
breakthrough concentration between 0.5 and 1, while some 75% of the 40 strains we tested
had similar attachment efficiency values in the order of 10
-3
and 10
-4
. Such observed sticking
efficiency homogeneity is in sharp contrast with our previous works (Foppen et al., 2010;
Lutterodt et al., 2009a,b) and observations made by other workers (Schinner et al., 2010;
Yang et al., 2008; Bolster et al., 2009, 2010), who observed significant variations in transport
among the various
E. coli
strains used in their experiments. Though it is difficult to explain
such observed homogeneity from
E. coli
surface characteristics (
Table 7.3
), the strains used
in this work were isolated from flow lines at their termination points (springs), and such
strains may therefore possess certain cell characteristics that might have influenced their
selective transport in the subsurface giving rise to their similar transport characteristics in our
columns.
In contrast to some workers (e.g. Bolster et al., 2006, 2010, Jacobs et al., 2007, Walker et al.,
2005), who reported that hydrophobicity and zeta potential play an important role in bacteria
transport, but consistent with our previous observations (Lutterodt et al., 2009a, Foppen et al.,
2010) and observations made by Bolster et al. (2009, 2010), our results demonstrated that
there was no statistically significant correlation between measured cell properties (zeta
potential, motility, cell size, cell aggregation, and hydrophobicity) and transport parameters (
f
,
Ω
and
k
and (C/C
0
)
max
). Bolster et al. (2010) explained that additional confounding
factors may be present when correlating
E. coli
transport to surface properties. In this work,
the lack of correlation between cell properties and bacteria attachment can be ascribed to the
homogeneity in Α
and the observed large variation in cell properties. In contrast to Foppen et
al. (2010), there was no correlation between
Α
and (C/C
0
)
max
. We attributed this to the fact
that all strains were not only subject to kinetic attachment, but also to equilibrium sorption.
This type of sorption was absent in the
E. coli
strains obtained from the Rotterdam Zoo in the
work of Foppen et al. (2010). In addition, Foppen and Schijven (2006) reported that, based on
a number of studies, equilibrium sorption in
E. coli
transport was of little significance (Pang
et al., 2003; Powelson and Mills, 2001; Sinton et al., 1997; Sinton et al., 2000; Alexander and
Seiler, 1983; Havemeister and Riemer, 1985, both in: Matthess et al., 1985 and in Matthess et
al., 1988; Champ and Schroeter, 1988; Merkli, 1975). Although the role equilibrium sorption
plays in most of the strains we used in this work was indeed also rather limited, the role of
kinetic attachment was at least equally limited. We do not have a good explanation for this
equilibrium sorption phenomenon we observed. Possibly it was inherent to the approach we
took in collecting
E. coli
strains: isolated from flow lines at their termination points (springs),
and these strains may therefore have possessed certain typical transport characteristics that
became apparent in our columns.
Another conclusion from our work was that 58% of the strains were of the O21:H7 serotype.
The O antigen of
E. coli
consists of many repeats of an oligosaccharide unit and forms part of
the lipopolysaccharide (LPS) molecule protruding from the outer membrane of an
E. coli
cell
into its immediate environment. The O antigen determines the serogroup of an
E. coli
and the
specific combination with the flagellar (H) antigen determines the serotype of an isolate
(Stenutz et al., 2006). LPS is anchored in the outer membrane of
E. coli
and occupies 75% of
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