Innovative use of lamella clarifiers for central storm- water treatment in separate sewer systems Utilisation innovante des décanteurs lamellaires pour le traitement des eaux pluviales dans les réseaux sépara- tifs

In the past years, lamella settlers have been used as devices for treatment by sedimentation also for storm water. Instead of just equipping a sedimentation basin with numerous lamella modules, an innovative approach for traditional separate systems is proposed. Basically, storm water is stored in a basin or tank during a rain event, while treatment is done in a small but continuously operated lamella clarifier unit. The advantages are a low throughput flow of the lamella clarifier, yielding a small-footprint unit having a good efficiency, moreover the possible use of existing storage volume, e.g. in an existing storm sewer, and also the structural flexibility of the arrangement. Finally, also the water volume which is fed together with the sludge to a treatment plant may be minimized. A simulation method is proposed in order to assess an equivalent degree of stormwater treatment, either by achieving an equal annual volume of treated storm water or, more directly, an equal amount of spilled pollutant load, expressed as Total Suspended Solids (TSS), both if compared with a conventional settling tank according to current German design rules. Finally, a project example is also demonstrated.