Biology Reference
In-Depth Information
In an effort to improve the prediction of colloid transport distances in the environment, we
recently introduced the so-called minimum sticking efficiency (Lutterodt et al., 2009a,
chapter 2
),
defined as the sticking efficiency belonging to a bacteria fraction of 0.001% of initial bacteria
mass flowing into a column, after removal of 99.999% (5 log reduction) of the original bacteria
mass has taken place. The minimum sticking efficiency practically represents the sticking
efficiency of a minor fraction of bacteria cells. However, within this minor fraction of bacteria
cells, the sticking efficiencies are again not a constant, but they are distributed, and therefore,
within this sub-fraction, the minimum sticking efficiency is the
highest
possible sticking
efficiency. Within a bacteria population, the fraction of cells possessing the minimum sticking
efficiency are those lacking properties (e.g. cell motility, fimbriae, presence of antigen-43, an
outer membrane protein of
E. coli
-Lutterodt et al., 2009a,
chapter 2
), that influence cell
attachment to collector grain surfaces and therefore have a relatively good ability to be
transported over longer distances. This minimum sticking efficiency can be obtained through
extrapolations from equations generated from (power-law) distributions of fractions of cells
retained and their corresponding sticking efficiencies. These distributions have not been studied
for large intra-column distances over long transport distances (> 5 m).
In this paper, a new approach in conducting bacteria transport experiments in the laboratory is
introduced. This involves the use of a flexible helix column packed with quartz sand saturated in
water. The main objectives are to measure sticking efficiencies that can be considered as
environmentally realistic, and to determine the minimum sticking efficiencies of two
Escherichia
coli
strains over relatively long transport distances of 25 m.
5.2 Materials and methods
5.2.1 Column set up and tracer experiment
The porous media consisted of 99.1% pure quartz sand (Kristall-quartz sand, Dorsilit, Germany)
with grain sizes ranging from 180 to 500 m, and a median grain size of 356 m. Though the
removal of chemical impurities from the surface of quartz grains may expose physical
imperfections like cracks, edges and lattice defects which may produce variation in the surface
charge (Stumm and Morgan, 1996) and can increase the attachment efficiency of bacteria, the
quartz grains was washed with acetone, hexane and concentrated HCl followed by repeated
rinsing with de-mineralised (DI) water until the Elecetrical conductivity of the effluent was very
low (< 3µS/cm). This was to ensure interaction between bacteria cells and pure quartz grains
with negligible influence of polar organics and polar in-organics which may also affect bacteria
attachment rates.
To form a helix column, a 26 m flexible tube reinforced with stainless steel (Armovin HNA-
Food production, Italy) and of diameter 3.2 cm was sealed at one end with a 50µ m nylon mesh.
The column was filled with the cleaned quartz sand under saturated conditions, while the sides of
the flexible tube were continuously tapped with a plastic hammer to avoid layering and or
trapping of air. The saturated column was then coiled around a 2.33 m diameter circular flexible
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