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A PROTOCOL FOR DETERMINING WWF SETTLING VELOCITIES FOR TREATMENT PROCESS DESIGN ENHANCEMENT
Citation:
O'Connor*, T P., J. Cigana, AND D. Fischer**. A PROTOCOL FOR DETERMINING WWF SETTLING VELOCITIES FOR TREATMENT PROCESS DESIGN ENHANCEMENT. Preparing for the 21st Century; Proceedings of the 26th Annual Water Resources Planning and Management Conference; June 6-9, 1999, Tempe, Arizona. Wilson, E.M. (Ed.). Reston, VA: American Society of Civil Engineers, 1999, 11 p, Tempe, AZ, 6/6-9/1999.
Description:
Urban wet weather flows (WWF) contain a high proportion of suspended solids (SS) which must be rapidly reduced before release to receiving waters. Site specific, storm-event data evaluations for designing WWF-treatment facilities differs from dry-weather flow design. WWF-settleable solids tend to build up in the sewer system as a function of the length of the antecedent dry-weather period, sewer slope, and drainage area soil characteristics. Thus, accurate assessment of settling velocity is essential for characterizing WWF and correctly designing control technologies. An innovative settling test was developed using a newly designed settling column configuration. The performance of the new configuration was compared to a traditional settling test in side-by-side measurements of SS and associated settling velocity distributions. Results from 15 laboratory bench-scale test are presented. The limitations and advantages (e.g., cost, setup requirements) of each approach will be presented.
One traditional method for determining SS-settling velocity uses a six- to eight-foot high, eight inch diameter column with samples withdrawn from side ports. This apparatus requires a large volume of analyte and many samples which require further analysis. The initial concentration is difficult to measure, due to the time lag required to fill the column prior to the first samples. This column test may also be inadequate for capturing larger, denser, faster settling particles.
Several European particle-settling-velocity methods which were specifically designed for the heavier particles in storm-generated flows require smaller testing volumes and apparatuses. The Centre d,Enseignement et de Recherche pour la Gestion des Ressources Naturelles et de l,Environnement (CERGRENE) of France developed a test that uses several small columns to analyze particle-settling velocities. This method was adapted for North American application. This project compares the CERGRENE method to a traditional column in a side-by-side evaluation.
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1 Environmental Engineer, Wet Weather Flow Research Program, Urban Watershed Management Branch, Water Supply and Water Resources Division, U. S. Environmental Protection Agency (EPA), Edison, New Jersey, 08837
2 John Meunier, Inc., Montreal, Quebec H4K 1K5
3 Oak Ridge Institute of Science and Education, Research Scientist, Edison, New Jersey 08837.