Summary, conclusions and recommendations - Transport of Multiple Escherichia Coli Transport in Saturated Porous Media - page 115

strains exhibited remarkably similar transport characteristics, with some 82 % having a
maximum relative breakthrough concentration between 0.5 and 1, while some 75% of the 40
E. coli strains had similar attachment efficiency values in the order 10 -3 and 10 -4 . This is
even though the attachment variation between two strains with the least (10 -7 ) and highest
(10 -2 ) sticking efficiencies resulted in a 5 log unit variation. The observed homogeneity is
attributable to the way in which the strains were harvested: from springs, and therefore at the
termination points of flow lines. 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.

Intra-strain attachment variations were observed for all E. coli strains used, regardless of the
source of isolation and growth medium. A general trend of reduction in sticking efficiencies
with increasing transport distances was observed. A summary of the long column results is
presented in Table 8.1 .

Table 8.1: Lowest measured values of sticking efficiencies ( Α L , Α I ) values and

extrapolated minimum sticking efficiency ( Α ) for long column (L ≥1.47)

min

transport experiments in artificial groundwater

Strain Source

of
isolation

Growth
medium

Column
length
(m)

Fraction
exiting the
column
(-)

Lowes Α L
(-)

Lowest Α I
(-)

Α

min

(-)

UCFL-71 Soils manure extract 4.83 2.6 × 10 -1 8.5 × 10 -2 4.7 × 10 -2 4.5 × 10 -6

UCFL-94 Soils manure extract

nutrient broth

4.83
25.65

2.5 × 10 -1
1.2×10 -3

6.0 × 10 -3
8.2 × 10 -6

6.1 × 10 -6
1.7 × 10 -7

2.1 × 10 -1
1.9 × 10 -1

UCFL-131 Soils manure extract

nutrient broth

4.83
25.65

3.5 ×10 -1
2.3×10 -4

2.8 × 10 -1
1.6 × 10 -5

9.4 × 10 -3
6.8 × 10 -8

<1 × 10 -6
8.7 × 10 -1

3.5×10 -1 1.4 × 10 -1 1.7 × 10 - 1 <1 × 10 -6

UCFL-167 Soils manure extract 4.83

3.6 ×10 -1 2.0 × 10 -1 3.4 × 10 - 2 <1 × 10 -6

UCFL-263 Soils manure extract 4.83

≥ 1 UCFL-348 Soils manure extract 4.83 >1 >1 n.d.

SL03 Spring nutrient broth 1.47 2.8 ×10 -2 1.2 × 10 -2 1.3 × 10 -5 3.4 × 10 -1

2.5 ×10 -2 1.3 × 10 -2 1.7 × 10 -4 4.2 × 10 -1

FR08 Spring nutrient broth 1.47

1.1 ×10 -2 2.0 × 10 -3 1.8 × 10 -4 2 .0 × 10 -2 FR02 Spring nutrient broth 1.47

FA03 Spring nutrient broth 1.47 5.5 ×10 -2 1.0 × 10 -2 8.1 × 10 -5 1.3 × 10 -1

SL20 Spring nutrient broth 1.47 1.5 ×10 -2 3.0 × 10 -3 4.7 × 10 -5 6.6 × 10 -1

9.3 ×10 -2 7.0 × 10 -2 3.0 × 10 -2

FR05 spring nutrient broth 1.47 ~0.1

Both segment sticking efficiency ( Α I ) and sticking efficiency measured over total transport
distances (Α L ) reduced with increasing column lengths and indicated intra-strain attachment
variations for all strains used for our long column transport experiments. In addition, we
concluded that environmentally relevant low values of sticking efficiencies in the order 10 -3
to 10 -6 were measurable in the laboratory, and the results demonstrated the importance of the
use of long columns. The measured low values of sticking efficiency show that, for bacterial
populations leaked into groundwater environments, sub-populations may posess non-
attaching characteristics and therefore increases their chances of being transported over
considerable distances.

Differences in cell attachment to quartz grains resulted in power-law distributions describing
the relation between E. coli sub-populations and corresponding sticking efficiencies. From
power-law equations, the minimum sticking efficiency defined above and in Chapters 3 and 4