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Modal Contact Time Tracer Studies in Two Chlorine Contact Tanks

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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.

Keywords: chlorine; concentration; contact tank; design; disinfection; flow rates; hydraulic retention time; modal contact time; residual; tracer tests

Document Type: Research Article


Publication date: January 1, 2010

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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