Lamella Settler for Storm Water Treatment - Performance and Design Recommendations Traitement des eaux pluviales avec décanteur lamellaire - Performances et recommandations pour le dimensionnement

Three lamella settlers, two situated at the overflow of a combined sewer system and one at the outlet of a separate sewer system, were monitored over a period of four years. The main objective was to determine removal efficiencies for total suspended solids and associated pollutants. For this purpose a new sampling method based on large volume solid samplers was developed allowing a detailed analysis of solids. In regard to total suspended solids the average removal efficiency of the plants range from 49 up to 68 %. Similar values could be achieved for phosphorus and heavy metals mainly because of the high portion of fine particles in treatment plants influent. A clear dependency between solid removal efficiency and the parameters maximum surface load and influent concentration could be observed on single event basis. The aggregation of all findings of this study result in a recommended maximum design surface loading rate (SLR) of 4 m/h. According to the results of this study a solid removal rate of 50 % which is defined as minimum long-term efficiency can be achieved safely at this SLR. In addition to the definition of the maximum SLR a proper dissipation of the inflow energy and an equal collection and discharge of the clear water above the lamella turn out to be essential.