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within 5 m. This order of magnitude corresponded well with the values found by Foppen and
Schijven (2006), who indicated that the range of sticking efficiencies of
Escherichia coli
for
geochemically heterogeneous sediment, based on a number of studies, ranged from 0.002 to 0.2.
However, one strain, UCFL-94, deviated from this general trend (minimum sticking efficiency =
6.06 ×10
-6
). We believe that this deviation was due to differences in surface characteristics of
UCFL-94 compared to the other strains, although we do not know what the differences were
exactly. This deviation most likely showed the importance of surface characteristics in the initial
attachment of
E. coli
cells, as was discussed above.
For the DI set of experiments, which we considered to be a worst case, with maximum transport
of
E. coli
cells, the minimum sticking efficiencies were much lower (as low as 10
-9
) than for the
AGW set. In literature, we could not find another example that presented such low sticking
efficiencies.
4.5 Conclusions
From the experimental results and observations the following conclusions can be drawn:
•
In both DI and AGW, for all
E. coli
strains we used, the computed lower values of Α from
the column experiments were in the same order of magnitude (10
-3
-10
-2
). However, for the DI
experiments, 1-36% of the initial bacteria mass must have had an
Α value less than the
lowest
Α values determined for the most distant column segments.
•
Our results showed that the power-law distribution described best the variations of Α -values
within the strains in both solutions (DI and AGW), although in AGW, the exponential
distribution was equally well capable of describing the distribution of
Α values.
Calculated minimum sticking efficiency values ranged from as low as 10-9 for UCFL-94 to
10
-2
for UCFL-348 in the DI water experiments, and from 10
-6
for UCFL-94 to
•
≥
1
for
UCFL-348 in the AGW experiments.
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