The study of the fate of bacteria in Coastal water shows that their concentrations can be
reduced by different processes such as physical dilution, floc sédimentation, and die-off.
Mathematical modeling allows the prédiction of bacterial dispersion in the Coastal zone.
Die-off processes were studied onEscherichia coli and Salmonella (classical fecal coliforms
used as indicator) ; results show the importance of Coastal water quality on the process and,
in poor water - Mediterranean sea -, bacteria die quickly ; by contrast, in the Atlantic and
the English channel, sédiments and suspended matter improve the survival of bacteria
1 because dissolved and particulate organic matter contains osmoprotectors and nutrients,
assimilated by fecal bacteria.
Moreover bactericidal solar radiation is attenuated by suspended matter. T90 (time for
disappearance of 90 % of bacteria) were calculated on two sites ; in clear water, with high
sunlight energy, these times are between 1 and 4 hours, whereas in estuarine zones, T90 are
' about several days. These results generalize some studies on mediterranean sea, which gave
1 lower value of T90.
Low die-off rates must be take into account to establish waste water disposai criteria in
4 shellfishing areas, because oysters and mussels can very quickly accumulate several ten
1 times fecal bacteria.
The improvement of waste water treatment and disposai must focus on :
1 - choice of disposai point using mathematical models of Coastal dilution,
f(
0 - maintenance of a high rate of micropollutant élimination,
ti
- réduction of micro-organism inputs in sensitive areas by spécifie treatments, like
1 filtration, infiltration or wastewater lagoons ; Chemical treatment such as chlorination
could be used, but high organic matter, suspended matter or ammonia concentrations
decrease the disinfection efficiency ; the disinfection rate may be measured using fecal
ni
•
•
indicator bacteria which may be more sensitive than pathogen micro-or gamsms,
12 - réduction, by spécifie treatment, of phosphorus and/or nitrogen inputs in eutrophicated
ei areas, where urban waste water disposai is greater than river inputs.
te
n
D
u
1
u
9
reduced by different processes such as physical dilution, floc sédimentation, and die-off.
Mathematical modeling allows the prédiction of bacterial dispersion in the Coastal zone.
Die-off processes were studied onEscherichia coli and Salmonella (classical fecal coliforms
used as indicator) ; results show the importance of Coastal water quality on the process and,
in poor water - Mediterranean sea -, bacteria die quickly ; by contrast, in the Atlantic and
the English channel, sédiments and suspended matter improve the survival of bacteria
1 because dissolved and particulate organic matter contains osmoprotectors and nutrients,
assimilated by fecal bacteria.
Moreover bactericidal solar radiation is attenuated by suspended matter. T90 (time for
disappearance of 90 % of bacteria) were calculated on two sites ; in clear water, with high
sunlight energy, these times are between 1 and 4 hours, whereas in estuarine zones, T90 are
' about several days. These results generalize some studies on mediterranean sea, which gave
1 lower value of T90.
Low die-off rates must be take into account to establish waste water disposai criteria in
4 shellfishing areas, because oysters and mussels can very quickly accumulate several ten
1 times fecal bacteria.
The improvement of waste water treatment and disposai must focus on :
1 - choice of disposai point using mathematical models of Coastal dilution,
f(
0 - maintenance of a high rate of micropollutant élimination,
ti
- réduction of micro-organism inputs in sensitive areas by spécifie treatments, like
1 filtration, infiltration or wastewater lagoons ; Chemical treatment such as chlorination
could be used, but high organic matter, suspended matter or ammonia concentrations
decrease the disinfection efficiency ; the disinfection rate may be measured using fecal
ni
•
•
indicator bacteria which may be more sensitive than pathogen micro-or gamsms,
12 - réduction, by spécifie treatment, of phosphorus and/or nitrogen inputs in eutrophicated
ei areas, where urban waste water disposai is greater than river inputs.
te
n
D
u
1
u
9