Modal Contact Time Tracer Studies in Two Chlorine Contact Tanks

Author: Porter Benjamin   Josse Juan   Spangenberg Carl   Hafner Keith  

Publisher: Water Environment Federation

ISSN: 1938-6478

Source: Proceedings of the Water Environment Federation, Vol.2010, Iss.16, 2010-01, pp. : 1268-1278

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Abstract

Chlorine contact tank (CCT) design is crucial for proper disinfection of treated wastewater effluent (recycled water). Appropriate dimensions must be utilized in order to ensure that contact times are adequate for complete disinfection. Tracer tests are conducted as required by the California Department of Public Health (DPH) Title 22 regulations to determine that the chlorine contact tank, as constructed, does indeed provide the minimum modal contact time (MCT) of 90 minutes for all anticipated flow rates. Similar Rhodamine dye tracer tests were performed on two CCTs. At each facility, the MCTs were obtained for several different flow rates, and these values were plotted to create curves from which the MCTs at a given flow rate for each facility could be obtained by interpolating from the given data points. The ratio of modal contact time to hydraulic retention time (efficiency) varied between the two CCTs and was apparently the result of tank geometry.