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reduction in fluid phase colloid concentration as travel distance increases. A characteristic of the
classical theory is the use of the sticking efficiency, which is defined by the ratio of the number
of particles that strike and stick to a collector to the number of particles striking a collector and is
mainly determined by electro-chemical forces between the colloid and surface of the collector.
Contrary to the classical theory, research results over the last two decades have indicated that the
sticking efficiency of a biocolloid population is not a constant, and the variations have been
attributed to variable cell 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,b). The variation of the deposition rate coefficient has been attributed to a number of
reasons, including geochemical heterogeneity on collector grain surfaces (Johnson and
Elimelech, 1996; Bolster et al., 2001; Loveland et al., 2003; Foppen et al., 2005), straining
(Bradford et al., 2002 and 2003; Bradford and Bettahar, 2005; Foppen et al., 2007a,b), and
heterogeneity of the colloid population due to variability in surface properties (Albinger et
al.,1994; Baygents et al., 1998.; Simoni et al., 1998; Li et al., 2004; Tufenkji and Elimelech,
2005a,b; Tong and Johnson, 2007). The variability in bacteria surface properties has been
attributed to variations in lipopolysaccharide (LPS) coating (Simoni et al.,1998), distribution of
the interaction potential within the bio-colloid population (Li et al., 2004), variations in surface
charge densities (Baygents et al.,1998; Tufenkji and Elimelech, 2004b), and differences in
energy needed to overcome the energy barrier (Tufenkji and Elimelech, 2004b). Some group of
workers (Redman et al., 2001a, b; Tufenkji et al. 2003) have demonstrated that a power-law best
describes the distribution of sticking. Others found a log-normal distribution (Tufenkji et al.,
2003; Tong and Johnson, 2007) or a dual distribution (Tufenkji and Elimelech, 2004b, 2005b;
Foppen et al 2007a). The deviation of bacteria deposition patterns from the CFT has resulted in
the inability to accurately predict transport distances in aquifers, with consequences of polluting
drinking water sources (springs, boreholes and wells).
1.4.
Escherichia coli
Escherichia coli
(
E. coli
), a gram-negative, facultative non-spore forming, rod shaped bacterium
is commonly used as indicator of faecal contamination of drinking water supplies, because
E.
coli
is a consistent, predominantly facultative inhabitant of the human gastrointestinal tract. In
addition,
E. coli
is easy to detect and quantify. Furthermore, the net negative surface charge and
low inactivation rates of
E. coli
ensure that they may travel long distances in the subsurface and
these characteristics make them a useful indicator for fecal contamination of groundwater (e.g.
Foppen and Schijven, 2006). Due to the importance of
E. coli
, 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). This thesis is looking into more detail at the
transport of
E. coli
in saturated porous media.
1.5
Problem statement and objectives
Experimental results over the past decade-and-a-half have indicated that biocolloid interactions
with saturated porous media vary within and among bacterial populations (Section 1.3). Results
over the period revealed a transport distance dependent sticking efficiency, sticking efficiency
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