Two settling devices treating rainwater from urban drainage areas and equipped with secondary sludge treatment were monitored over a period exceeding one year. The two devices differ in their design and in the quantity and quality of effluents received. Full analyses over approximately 30 mean samples of the intake and discharge effluents allowed judgment of the mean efficiency of pollution control and the reduction in impact of the storm water. The observed settlement was compared to measurements of settling velocity during several rainfalls. From analyses of the settled or extracted sludge it was possible to characterize the pollutants retained in the sludge. Particular attention was paid to the functioning and operation of the devices.

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