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Escherichia coli
for geochemically heterogeneous sediment, based on a number of studies,
ranged from 0.002 to 0.2.
Because of the importance of knowing the characteristics of a sticking efficiency distribution of a
biocolloid population for long transport distances, the present work aimed at determining types
of sticking efficiency distributions of 6
Escherichia coli
strains and their minimum sticking
efficiencies in relatively high columns (5 m) of saturated quartz sand. To enhance comparison
with environmental conditions, we only used
E. coli
strains isolated from the environment.
Furthermore, the strains were grown for environmentally realistic conditions, and the chemical
quality of the bacteria suspensions we used was close to environmental conditions
4.2 Materials and methods
4.2.1 Bacteria growth and column experiments
Six
Escherichia coli
(
E. coli
) strains (UCFL-71, UCFL-94, UCFL-131, UCFL-167, UCFL-263
and UCFL-348) were obtained from the soil of a pasture used for cattle grazing (Yang et al.,
2004),
E. coli
isolates were grown in an extract of filter-sterilized (mesh size: 0.45 m) cow
manure to mimic environmental conditions. To do this, fresh cow manure was collected from a
farm (biological farm Ackersdijk, Delft), and stored at -20 °C in batches of 50 gram. Prior to
every experiment, a batch of 50 gram cow manure was defrosted and mixed with de-mineralized
(DI) water at a 1:20 ratio (EPA - 1312 Leach Method). Manure extraction was facilitated by
acidifying the mixture to a pH of 5±0.05 with concentrated sulphuric acid and nitric acid at 60/40
weight percent mixture, and extraction was performed for 2 hours. The mixture was then
centrifuged (IEC Centra GP 8- rotar 218/18cm) for 10 min at 4600 rpm, and then at 9000 rpm for
10 min (MSE high speed 18). The supernatant was sequentially filtered through a 0.45 m and a
0.2 m mesh size cellulose acetate membrane filter (47mm diameter)
. E. coli
isolates were
activated from a holy tube (pepton agar stock) in Luria Bertani Broth (DifcoTM LB Broth,
Miller) for 6 hours at 37 °C while shaking at 120 rpm on an orbital shaker. The inoculum was
then diluted 10
5
fold in the cow manure extract and incubated, while shaking on the orbital
shaker at 120 rpm, for 72 hours at 21 °C until a stationary growth phase was reached at a
concentration of ~10
8
cells/ml.
To study the distributions in sticking efficiency the
E. coli
strains, column experiments were
conducted in demineralised (DI) water and in artificial groundwater (AGW). AGW was prepared
by dissolving 526 mg/L CaCl
2
.2H
2
O and 184 mg/L MgSO
4
.7H
2
O, and buffering with 8.5 mg/L
KH
2
PO
4
, 21.75 mg/L K
2
HPO
4
and 17.7 mg/L Na
2
HPO
4
. The final pH-value ranged from 6.6 to
6.8 and the Electrical Conductivity (EC)-value ranged from 1025 to 1054 S/cm. The porous
media comprised of 99.1% pure quartz sand (Kristall-quartz sand, Dorsilit, Germany) with sizes
ranging from 180 to 500 m, while the median of the grain size weight distribution was 356 m.
With this grain size, we excluded straining as a possible retention mechanism in our column:
assuming a bacteria equivalent spherical diameter of 1.5 m, the ratio of colloid and grain
diameter was 0.004, which was well below the ratio (0.007) for which straining was observed by
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