A tracer test was performed in a 3,000 m3 and 1 m deep maturation pond located in the south of France. A retention time distribution was determined on the basis of tracer study. Tracer distribution into the pond was also monitored. Physico-chemical parameters and faecal coliform contents were measured at pond inlet and outlet and at 4 points in the pond. During the same period, two 20 m3 and 1 m deep pilot pools were set close to the pond and filled with inlet water. A die-off constant was calculated after the variations of feacal coliform contents observed in the pilot pools. The objective was to verify whether faecal coliform removal can be predicted from observed retention time distribution, assuming a first-order faecal coliform decay with a die-off constant determined in pilot pools. A very good prediction was achieved despite some uncertainties in the experimental data mainly due to pond operation and climatic conditions.

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