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  Testing Solids-Settling Apparatuses for Design and Operation of Wet-Weather Flow Solids/Liquid Separation Processes, Research Report (160 pp, 2.05 MB) (EPA/600/R-02/090) October 2002

This study was a side-by-side comparison of two settling column tests: one traditional and one new. The new apparatus was developed by the Centre d'Enseignement et de Recherche pour la Gestion des Ressources Naturelles et de l'Environnement (CERGRENE) of France and uses several small columns to sequentially measure particle-settling velocities. The new apparatus was compared with a larger, more traditional column, which has been widely used as a research and academic tool but is difficult to transport and set up in a field location due to its size. The new method was thought to be more amenable to field use because of ease of transport and sampling and the limited number of samples generated.

The study was conducted in three phases: fabrication and preliminary testing, laboratory testing, and field testing. Equipment for the two testing methods was fabricated and laboratory tested and preliminary evaluations were made. Laboratory tests were conducted with two well-characterized settling media, microsand and clay soil, in order to measure suspended solid concentrations and develop settling distributions of known substances in the columns prior to testing actual wet-weather flow, which exhibits variable suspended solid concentrations and settling distributions. Field tests were conducted at a combined sewer control structure to compare the performance of the two columns when filled with combined sewage.

A summary of the performance, as measured by predicted percent removal of both columns for 15 laboratory tests and 3 field tests, is presented, as well as a comparison of the advantages and disadvantages of the two methods. The new testing method (CERGRENE) did not perform up to the anticipated theoretical expectations of the method. The report ends with conclusions and recommendations regarding the two specific methods and the settling column tests in general.


Thomas O'Connor

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