equipped by a combined sewer network, urban runoff waters
significantly increase the flow entering the WWTP during
rain events. It may become unable to handle the entire
flow of wastewater and untreated or partially treated
(bypass certain stages of purification treatment) waters
that are released into the environment. The content of
microorganisms and indicators of CSO is generally lower
than those of raw sewage entering the WWTP during dry
weather due to the dilution of domestic waters by runoff
waters less rich in microorganisms (Marsalek and Rochfort
2004). However, the sudden and important flow increase
occurring during storm events can cause resuspension of
fecally contaminated sediments accumulated in the pipes
of the sewer during dry weather periods. The type of situation encountered depends on network characteristics (size,
slope, etc.) and those of the rainy event (intensity, duration,
etc.). In the case of urban areas with separate sewer
networks, runoff waters are commonly discharged directly
into the receiving water without any treatment. In both
scenarios, the intake flow of pathogenic microorganisms is
increasing in rainy conditions. These observations explain
why the most critical situations of microbiological environmental water quality are monitored just after storm or rain
periods (e.g., degraded microbiological quality of bathing
waters after summer storms).
15.6.2 Diffuse Sources
The inputs of microorganisms from fecal origin via nonpoint
sources are relatively difficult to quantify. The
concentrations of FIB has been determined in small streams
upstream of any source of domestic contamination in order
to get a rough estimate of the levels of contamination due to
runoff waters and soil leaching. These studies have shown
that the measured concentrations were very different
depending on the landuse of the watershed. Streams whose
catchment area is mainly covered with pastures presented
contamination levels one order of magnitude higher than the
streams whose catchment area is covered mainly by forest or
crops. For example, in a study conducted in the Seine river
watershed (France), average E. coli concentrations around
400/100 mL were found in small rivers flowing in pastured
areas, while they were around 40/100 mL in streams flowing
in forest and culture areas (Garcia Armisen and Servais
2007). This clearly highlights the importance of manure
grazing livestock as a source of fecal contamination of
surface waters in agricultural areas.
It was also shown that the contribution of fecal bacteria in
grazing areas depended on the intensity of precipitation.
In rainy periods, the flux exported to aquatic systems is
increasing due to the greater contribution of runoff waters
that are richer in fecal microorganisms than baseflow fed by
water that seeped through the ground. Indeed, the
percolation of water through the soil leads to a natural
removal of microbial contamination. Indeed, the technique
to infiltrate water through soil horizons is also used in some
countries for the production of drinking water.
15.7 Fate and Transport of Enteric
Microorganisms in the Environment
The fate of enteric microorganisms in the environment is
very difficult to assess because current methods (cf. Sect. 14.
10) make it difficult to follow them from their natural reservoir to another point. In addition, their fate is variable
depending on the nature and intensity of environmental
pressures experienced throughout their route to the point
of contact with humans. Environmental factors that may
influence the fate of a pathogen into the environment are
multiple (Fig. 15.8). They contribute to the self-purification
of the natural environment, and they are sometimes used to
purify water, as in the case of waste stabilization ponds.
The transport of enteric microorganisms in aquatic
environments is controlled by the hydrodynamics of the
system in which they are released and in some cases by
settling. Concerning the fate of fecal microorganisms, it is
quite usual to distinguish two types of controlling factors:
the biotic and the abiotic factors.
15.7.1 The Hydrodynamical Factors
Enteric microorganisms released in rivers (e.g., by the effluent of a WWTP) are diluted by the river water, and their
transport is mainly controlled by the river flow. The impact
of dilution, diffusion, and transport is much more complex in
coastal areas. It is thus sometimes necessary to conduct
tracing operations to locate the point of discharge of sewage
and understand their fate in the ecosystem. Figure 15.9
shows aerial tracing with rhodamine* in a coastal area.
Rhodamine is a red dye. It is injected in high concentration
at a given point (here it was mixed in the effluent of a
WWTP) and then emerges a few minutes later at sea outfall
(end of the pipe often equipped with a vertical diffuser) and
diffuses into coastal waters. Measurements of the color
intensity over time and at various points are used to determine the diffusion parameters and thus to better understand
the impact of wastewater in the coastal environment.
Sedimentation is an important factor contributing to the
removal of some pathogens from the water column of
aquatic environments and to the accumulation of these
microorganisms in the sediments. Protozoa but also viruses
and pathogenic bacteria associated with particles can settle
in areas with little turbulence. They accumulate on the
bottom where they constitute a secondary reservoir which
can be a source of water contamination in some of the
15 Environmental and Human Pathogenic Microorganisms
645
significantly increase the flow entering the WWTP during
rain events. It may become unable to handle the entire
flow of wastewater and untreated or partially treated
(bypass certain stages of purification treatment) waters
that are released into the environment. The content of
microorganisms and indicators of CSO is generally lower
than those of raw sewage entering the WWTP during dry
weather due to the dilution of domestic waters by runoff
waters less rich in microorganisms (Marsalek and Rochfort
2004). However, the sudden and important flow increase
occurring during storm events can cause resuspension of
fecally contaminated sediments accumulated in the pipes
of the sewer during dry weather periods. The type of situation encountered depends on network characteristics (size,
slope, etc.) and those of the rainy event (intensity, duration,
etc.). In the case of urban areas with separate sewer
networks, runoff waters are commonly discharged directly
into the receiving water without any treatment. In both
scenarios, the intake flow of pathogenic microorganisms is
increasing in rainy conditions. These observations explain
why the most critical situations of microbiological environmental water quality are monitored just after storm or rain
periods (e.g., degraded microbiological quality of bathing
waters after summer storms).
15.6.2 Diffuse Sources
The inputs of microorganisms from fecal origin via nonpoint
sources are relatively difficult to quantify. The
concentrations of FIB has been determined in small streams
upstream of any source of domestic contamination in order
to get a rough estimate of the levels of contamination due to
runoff waters and soil leaching. These studies have shown
that the measured concentrations were very different
depending on the landuse of the watershed. Streams whose
catchment area is mainly covered with pastures presented
contamination levels one order of magnitude higher than the
streams whose catchment area is covered mainly by forest or
crops. For example, in a study conducted in the Seine river
watershed (France), average E. coli concentrations around
400/100 mL were found in small rivers flowing in pastured
areas, while they were around 40/100 mL in streams flowing
in forest and culture areas (Garcia Armisen and Servais
2007). This clearly highlights the importance of manure
grazing livestock as a source of fecal contamination of
surface waters in agricultural areas.
It was also shown that the contribution of fecal bacteria in
grazing areas depended on the intensity of precipitation.
In rainy periods, the flux exported to aquatic systems is
increasing due to the greater contribution of runoff waters
that are richer in fecal microorganisms than baseflow fed by
water that seeped through the ground. Indeed, the
percolation of water through the soil leads to a natural
removal of microbial contamination. Indeed, the technique
to infiltrate water through soil horizons is also used in some
countries for the production of drinking water.
15.7 Fate and Transport of Enteric
Microorganisms in the Environment
The fate of enteric microorganisms in the environment is
very difficult to assess because current methods (cf. Sect. 14.
10) make it difficult to follow them from their natural reservoir to another point. In addition, their fate is variable
depending on the nature and intensity of environmental
pressures experienced throughout their route to the point
of contact with humans. Environmental factors that may
influence the fate of a pathogen into the environment are
multiple (Fig. 15.8). They contribute to the self-purification
of the natural environment, and they are sometimes used to
purify water, as in the case of waste stabilization ponds.
The transport of enteric microorganisms in aquatic
environments is controlled by the hydrodynamics of the
system in which they are released and in some cases by
settling. Concerning the fate of fecal microorganisms, it is
quite usual to distinguish two types of controlling factors:
the biotic and the abiotic factors.
15.7.1 The Hydrodynamical Factors
Enteric microorganisms released in rivers (e.g., by the effluent of a WWTP) are diluted by the river water, and their
transport is mainly controlled by the river flow. The impact
of dilution, diffusion, and transport is much more complex in
coastal areas. It is thus sometimes necessary to conduct
tracing operations to locate the point of discharge of sewage
and understand their fate in the ecosystem. Figure 15.9
shows aerial tracing with rhodamine* in a coastal area.
Rhodamine is a red dye. It is injected in high concentration
at a given point (here it was mixed in the effluent of a
WWTP) and then emerges a few minutes later at sea outfall
(end of the pipe often equipped with a vertical diffuser) and
diffuses into coastal waters. Measurements of the color
intensity over time and at various points are used to determine the diffusion parameters and thus to better understand
the impact of wastewater in the coastal environment.
Sedimentation is an important factor contributing to the
removal of some pathogens from the water column of
aquatic environments and to the accumulation of these
microorganisms in the sediments. Protozoa but also viruses
and pathogenic bacteria associated with particles can settle
in areas with little turbulence. They accumulate on the
bottom where they constitute a secondary reservoir which
can be a source of water contamination in some of the
15 Environmental and Human Pathogenic Microorganisms
645