ENV4001_s10_hw7 - ENV 4001: ENVIRONMENTAL SYSTEMS...

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p. 1/4 ENV 4001: E NVIRONMENTAL S YSTEMS E NGINEERING Spring 2010 University of South Florida Homework #7 Civil & Environmental Eng. Due: Friday , Mar. 19 Prof. J.A. Cunningham 1. (26 pts) Imagine you are designing a water treatment system for the city of Mudville. The design flow rate is 10 million gallons per day. 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 μ m. These particles are approximately spherical in shape and they have a density ρ 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 π α G Ω N where N is the number concentration of particles, α is a collision efficiency assumed equal to 0.8, and Ω is the volume concentration of flocs in the basin, which depends on
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This note was uploaded on 06/12/2011 for the course ENV 4001 taught by Professor Staff during the Fall '08 term at University of South Florida - Tampa.

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ENV4001_s10_hw7 - ENV 4001: ENVIRONMENTAL SYSTEMS...

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