The residence time distribution of a cross-baffled serpentine chlorination tank was determ...

The residence time distribution of a cross-baffled serpentine chlorination tank was determined by injecting a pulse of 200 g of dissolved rhodamine dye into the influent. The tank is 9.4 m long and 6.7 m wide, with a longitudinal wall in the center. Each side has three baffle walls extending 2.5 m in from the outside wall and two extending in from the center wall to direct the serpentine flow pattern. The wastewater effluent enters through a channel near the top of the lank and discharges over an outlet weir. At the operating water depth of 2.55 m, the liquid volume is 137 m3 (excluding the volume occupied by the concrete walls). The test was conducted at the peak hourly flow rate of 10,100 m3/d. Effluent sampling times in minutes after injecting the dye and corresponding dye concentrations arc listed below. The dye concentrations were determined by measuring absorbance with a spectrophotometer at a wave-length of 550 μm. From these data, plot the tracer response curve C (mg/l) versus t (min). Calculate and locate the mean residence time  and the theoretical mean residence lime tR. In order to normalize the concentration lest data, the value of CΔ must be determined. A portion of the dye adsorbed onto the walls of the tank and became trapped in stagnant water in the corners and near the bottom at the inlet and outlet. Therefore, CΔ must be based on the calculated quantity of dye recovered in the effluent rather than on the amount injected. To estimate the milligrams of dve discharged, determine the area under the C-versus t tracer - response curve in milligrams • minutes/liter and multiply this value by the flow rate in liters/minute. The CΔ value is this amount of dye divided by the volume of water in the lank, which is equal to 137 m3. Calculate  and the peak normalized concentration Cpeak/CΔ.