Biology Reference
In-Depth Information
8.1 Point of departure and scope
Groundwater, one of the most important sources of water for drinking water supplies in many
regions of the world is under threat by microbial pathogenic contamination due to
anthropogenic activities. An effective way of protecting the resource from contamination,
especially, by pathogenic microorganisms leaking into an aquifer, is by delineating protection
areas around a drinking source. Surface water can also be effectively treated by passage
through sand to remove pathogens provided travel distances and times are adequate (e.g.
Tufenkji et al., 2003, Schijven, 2001). These strategies rely upon effective natural attenuation
of microorganisms by soils over set back distances (e.g. Taylor et al., 2004), and it is
dependent on the interaction between cells and aquifer media resulting in cell retention. Even
though natural processes may assist in the reduction of pollution and it is widely utilized in
soil aquifer treatment sites, most biological contaminants can travel long distances through
soils and aquifers until they are discharged into streams or wells (Corapcioglu and Haridas,
1985).
To predict the presence of pathogens in water, a separate group of microorganisms, generally
known as faecal indicator organism are used; one of the most important indicators used
worldwide is
Escherichia coli
. Due to the importance of
E. coli
as faecal indicator bacteria,
considerable attention has been given to understanding their transport and fate in saturated
porous media (e.g. Foppen et al, 2007a.b, Schinner et al., 2010, Bolster et al., 2010). Even
though column experiments have the disadvantage of the inability to simultaneously study the
various factors that influence
E. coli
transport in the subsurface, a unique advantage
associated with using columns is the provision of a great degree of control (Shani et al., 2008,
Harvey and Harms, 2002), and this allows the possibility of isolating and studying specific
factors affecting colloid transport. Results from column experiments are traditionally
modeled using the CFT (Yao et al., 1971), which provides an important framework for
predicting transport of
E. coli
in saturated porous media (Foppen, 2007). A unique
characteristic of the theory is the application of the sticking efficiency to predict colloid
transport distances in aquifers, the sticking efficiency is defined in
Chapter 1
as the ratio of
the rate of particles striking and sticking to a collector to the rate of particles striking a
collector, and is mainly determined by electro-chemical forces between the colloid and the
surface of the collector. According to the theory, the sticking efficiency is constant in time
and distance (Yao et al., 1971; Tufenkji and Elimelech, 2004a).
Contrary to the CFT, research results have indicated that the sticking efficiency of a bio-
colloid population varies due to variable surface properties of individual members of the
population, resulting in differences in affinity for collector surfaces (Albinger et al., 1994;
Baygents et al., 1998.; Simoni et al., 1998; Li et al., 2004; Tufenkji and Elimelech, 2005a;
Tong and Johnson, 2007; Foppen et al., 2007a) and contribute to distributions in bacteria
attachment efficiency.
This research involved the study of the transport of various
E. coli
strains isolated from
different sources of the environment (feces and different parts of zoo animals, soils of a
pasture used for animal grazing, and springs). In addition, prior to experiments, strains were
grown in cow manure at 21
o
C (
Chapters 2
and
4
) to mimic environmental conditions (Yang
et al., 2006) or in nutrient broth at 37
o
C (
Chapters 3
, and
5
-
7
) comparable to intestinal
conditions, the optimal growth temperature for
E. coli
. E
xperiments were conducted under
laboratory controlled conditions with a constant range of quartz grain sizes saturated with low
and high ionic strength solutions in columns of lengths up to 25 m. In addition, a constant
Search WWH ::
Custom Search