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p. 1/3 ENV 4001: E NVIRONMENTAL S YSTEMS E NGINEERING Spring 2011 University of South Florida Homework #3 Civil & Environmental Eng. Due: Wed., Feb. 2, 2011 Prof. J.A. Cunningham Each homework assignment will be graded on a 100-point scale. For this assignment, point values of each problem are indicated. 1. (20 pts) Municipal wastewater (sewage) is usually treated by a method called “activated sludge.” We’ll learn more about that later in the semester. Below is a schematic diagram that shows the process. Plant influent Q I = 100 m 3 /hr X I = 130 mg/L Aeration basin V = 1200 m 3 X = ?? mg/L Clarifier Plant effluent Q E = 95 m 3 /hr X E = 15 mg/L Sludge recycle Q R = 30 m 3 /hr Waste sludge Q W = ?? m 3 /hr X W = 9500 mg/L The aeration basin is a completely-mixed flow reactor (CMFR) where the sewage is degraded by bacteria. It has a high concentration of suspended solids; we use the symbol X to indicate the concentration of suspended solids in the aeration basin. Because we don’t want to release a lot of suspended solids into the environment, the effluent from the aeration basin goes to a clarifier . In the clarifier, the suspended solids settle to the bottom under the influence of gravity. Therefore, the plant effluent that comes out of the top of the clarifier has a low concentration of suspended solids (denoted X E ). The sludge that comes out the bottom of the clarifier has a very high concentration of suspended solids. A fraction of the
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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.

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