ENV4001_s11_hw7 - ENV 4001 ENVIRONMENTAL SYSTEMS ENGINEERING Spring 2011 Homework#7 Due Wed March 9 2011 University of South Florida Civil

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p. 1/4 ENV 4001: E NVIRONMENTAL S YSTEMS E NGINEERING Spring 2011 University of South Florida Homework #7 Civil & Environmental Eng. Due: Wed., March 9, 2011 Prof. J.A. Cunningham Assignment for 2011: Problems 1–4 (skip problem 5) Imagine you are designing a water treatment system for the city of Mudville. The design flow rate is 10 million gallons per day, which is equivalent to 0.438 m 3 /s. 1. (26 pts) One of your colleagues already designed a rapid-mix system to add alum to the water as a coagulant. Now, you need to design the flocculation basin. You decide to implement flocculation in three stages, i.e., in three completely-mixed flow reactors operated sequentially. This is a pretty typical design for flocculation. In each of these three basins, you aim to reduce the particle concentration by 85%. The residence time in each of the three basins is 10 minutes. The influent water has a concentration of particles equal to N 0 = 3.6 10 11 particles/m 3 , and the diameter of the particles is d = 0.5 m. These particles are approximately spherical in shape and they have a density s = 2.5 g/cm 3 = 2500 kg/m 3 . a. (4 pts) Calculate the concentration of particles (in number of particles per m 3 ) exiting the third flocculation basin. How much overall reduction did you achieve in terms of the number concentration? b. (13 pts) Calculate the average velocity gradient, G , in each of the three basins. Report your answer in units of sec –1 . You can get G if you know that the rate of particle flocculation (in units of particles per volume per time) is given by R 4 G N where N is the number concentration of particles, is a collision efficiency assumed equal to 0.8, and is the volume concentration of flocs in the basin, which depends on the dose of coagulant. You may assume that is equal to 1.0 10 –4 in the first basin, 1.6 10 –4 in the second basin, and 2.6
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This note was uploaded on 01/02/2012 for the course ENV 4001 taught by Professor Staff during the Spring '08 term at University of South Florida - Tampa.

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ENV4001_s11_hw7 - ENV 4001 ENVIRONMENTAL SYSTEMS ENGINEERING Spring 2011 Homework#7 Due Wed March 9 2011 University of South Florida Civil

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