Mechanisms implied in Escherichia coli removal during wastewater treatment
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Fecha
2011-08Autor
Garaizabal Ruiz, Idoia
Oruño Beltrán, Maite
Bravo, A.
Parada Morais, Claudia Bruna
Barcina López, María Isabel
Metadatos
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12th Symposium on Aquatic Microbial Ecology (SAME12)
Resumen
The wastewater treatment reduces the assimilable organic fraction and the number
of microorganisms of the effluents due to biological treatment and to the concentration
of bacteria in sludge after settling. Recycling of sludge as an organic
fertilizer is environment friendly but some pathogens could be concentrated in it.
To make an integral tracing of E. coli during the activated sludge treatment, the fate
of gfp-tagged cells were analysed in batch and pilot plant experiments.
The exposure of E. coli to wastewater in absence of microbial population did not
induce the entry into the viable but nonculturable state. The wastewater microbial
populations showed a different relation with E. coli survival process. The presence
of bacteriophages did not affect the survival while decrease in population was
related with the presence of protozoa. Moreover, the wastewater bacteria behaved
as predation-escaping prey and maintained their population density, while the E.
coli were predated.
Wastewater pilot plants prove an accurate model of a large scale plant. In our
experiments, when pilot plant reached equilibrium, E. coli counts in aqueous
fractions were stabilised about 104 cells ml-1 and in flocs or in sludge about
108 cells g-1. When addition of inoculated wastewater was stopped, the plant
continued working with non-inoculated influent. Number of gfp-tagged E. coli in
aqueous fraction diminished progressively and, after 2 d, it was below the detection
limit. However, for the same period, 106 cells g-1 remained adhered to flocs and
sludge.
In conclusion, despite the efficacy of the protozoa removing E. coli from
wastewater, this bacterium is not totally eliminated by treatment but mainly
concentrated in sludge.