Flocculation: Design Example The ideal situation, according to Zurcher, is "tapered flocculation," where the velocity gradient slowly decreases through the basin. "As larger flocs form, they break apart more easily and are more likely to run into each other," he says. "So less mining becomes helpful." Problem #2 Please design a tapered flocculation system for a 13 mgd water treatment plant. The flocculation system will be designed using the following criteria: 1. The basin is to be a crossflow horizontal-shaft paddle-wheel type system with a mean velocity gradient of 27 sec1 The design parameter for flocculation is given by a dimensionless 2. Detention time = 45 minutes number Gt, where is the velocity gradient and is the detention time. Values of Gt ranging from 104 to 105 are commonly used, with tranging 3. GT value between 50,000 to 100,000 from 10 to 30 min 4. The values of the three compartment tapered flocculation system are 50, 20, and 10 sec ! 5. Width of flocculation basin (total) = 90-ft 6. The flocculation is carried out using paddle wheels that are 6-inches in width and 10-ft in length. Each paddle wheel has 6 paddles, with 12-inch spacing in between each paddle. The outside blade of the paddle wheel should be 1-ft beneath the water surface and 1-ft above the bottom of the mixing chamber. 7. Adjacent paddle wheels should have a clear spacing of 30-36 inches between the blades. 8. The wall clearance is 12-18 inches. 2. The paddle-wheel design (check % cross-sectional area), need to start with assuming a typical paddle wheel design