U sing Phages for Characterization of Effluent Quality in a Stabilization Pond
413
Despite their operational simplicity, the pathogen removal mechanisms in WSP
are not well established yet. The mechanisms involve a series of complex
physical, chemical and biological interactions and despite a considerable amount
of research the results are conflicting. However, the main environmental factors
are thought to be sunlight, pH and dissolved oxygen (Maynard et aI., 1999).
Residence time is considered to be among the most important parameters, which
influence pond performance with respect to the removal and elimination of
pathogenic and parasitic microorganisms (Frederick and Lloyd, 1996). Waste
stabilization reservoirs (WSR) are especially useful in arid and semi-arid areas.
They were developed in Israel to store the effluent from a WSP system when it is
not required for irrigation, but soon the polishing treatment performed by the
reservoirs (i.e. extra BOD and coliform removal) became clear (Juanico and
Shelef, 1994).
1.3 Pathogen Indicators in Wastewater
The wastewater may content a variety of pathogenic microorganisms. These
pathogens can be discharged into natural waters and constitute a risk of
transmission of waterborne disease to the human population. If the effluent is used
for irrigation, pathogenic microorganisms can survive for extended periods of time
in plants and soils, with the subsequent risk for human health (Campos, 1998;
Campos et aI., 1998). Suitable monitoring of the water supply for the presence of
pathogens can assist in preventing disease from these sources.
Since the pathogenic microorganisms appear at low concentrations in WSP
effluent and the techniques available for the selective recovery and enumeration
require specialized laboratories, are very expensive and time consuming, several
indicator microorganisms are commonly used to evaluate the fecal pollution
degree of the water for routine monitoring. Diverse criteria have been proposed
for an ideal microbial indicator of pathogens (Yates, 1992). There is no organism
that fulfills completely these criteria, but few are close to it and these are the one's
used as fecal and pathogen indicators in water quality analysis. Fecal coliforms are
the principal microbial indicator organisms used for waste treatment system
monitoring. However, the use of these organisms does not reflect the viral
pollution of the effluent due to the poor correlation with virus occurrence and
persistence in treatment processes. Therefore, bacteriophages have been proposed
as enteric virus pollution indicators, as their morphology and survival
characteristics closely resemble that of some of the important human virus groups
and their detection and enumeration is easy and rapid (Kott et aI., 1978; Havelaar
et aI., 1993).
Three groups of organisms are currently of interest, the somatic coliphages, the
F -specific bacteriophages and the phages of the anaerobic bacterium Bacteroides
fragilis.
Somatic coliphages are phages that infect E.coli by adsorbing to receptors
situated in the cell wall. The F-specific phages specifically adsorb to the F or sex
pilli of the cell. (IA WPRC, 1991). Phages infecting anaerobic bacteria such as
413
Despite their operational simplicity, the pathogen removal mechanisms in WSP
are not well established yet. The mechanisms involve a series of complex
physical, chemical and biological interactions and despite a considerable amount
of research the results are conflicting. However, the main environmental factors
are thought to be sunlight, pH and dissolved oxygen (Maynard et aI., 1999).
Residence time is considered to be among the most important parameters, which
influence pond performance with respect to the removal and elimination of
pathogenic and parasitic microorganisms (Frederick and Lloyd, 1996). Waste
stabilization reservoirs (WSR) are especially useful in arid and semi-arid areas.
They were developed in Israel to store the effluent from a WSP system when it is
not required for irrigation, but soon the polishing treatment performed by the
reservoirs (i.e. extra BOD and coliform removal) became clear (Juanico and
Shelef, 1994).
1.3 Pathogen Indicators in Wastewater
The wastewater may content a variety of pathogenic microorganisms. These
pathogens can be discharged into natural waters and constitute a risk of
transmission of waterborne disease to the human population. If the effluent is used
for irrigation, pathogenic microorganisms can survive for extended periods of time
in plants and soils, with the subsequent risk for human health (Campos, 1998;
Campos et aI., 1998). Suitable monitoring of the water supply for the presence of
pathogens can assist in preventing disease from these sources.
Since the pathogenic microorganisms appear at low concentrations in WSP
effluent and the techniques available for the selective recovery and enumeration
require specialized laboratories, are very expensive and time consuming, several
indicator microorganisms are commonly used to evaluate the fecal pollution
degree of the water for routine monitoring. Diverse criteria have been proposed
for an ideal microbial indicator of pathogens (Yates, 1992). There is no organism
that fulfills completely these criteria, but few are close to it and these are the one's
used as fecal and pathogen indicators in water quality analysis. Fecal coliforms are
the principal microbial indicator organisms used for waste treatment system
monitoring. However, the use of these organisms does not reflect the viral
pollution of the effluent due to the poor correlation with virus occurrence and
persistence in treatment processes. Therefore, bacteriophages have been proposed
as enteric virus pollution indicators, as their morphology and survival
characteristics closely resemble that of some of the important human virus groups
and their detection and enumeration is easy and rapid (Kott et aI., 1978; Havelaar
et aI., 1993).
Three groups of organisms are currently of interest, the somatic coliphages, the
F -specific bacteriophages and the phages of the anaerobic bacterium Bacteroides
fragilis.
Somatic coliphages are phages that infect E.coli by adsorbing to receptors
situated in the cell wall. The F-specific phages specifically adsorb to the F or sex
pilli of the cell. (IA WPRC, 1991). Phages infecting anaerobic bacteria such as