Design a flocculation basin for water at 10°C flowing at Q = 49,200 m3/day for a typical process. train in a drinking water treatment plant. The basin shall be a cross-flow, horizontal-shaft, paddlewheel type with an average velocity gradient of G = 26.7 sec−1
1) Design a flocculation basin for water at 10°C flowing at Q = 49,200 m3/day for a typical process.
train in a drinking water treatment plant. The basin shall be a cross-flow, horizontal-shaft, paddlewheel type with an average velocity gradient of G = 26.7 sec−1
, a detention time τ = 45 minutes,
and a Gτ value of 50,000 to 100,000. Tapered flocculation shall be used in three compartments of
equal depth in series. Compartments shall be separated by slotted, redwood baffle fences and
have a level basin floor. G-values shall be 50, 20, and 10 sec−1 as the water passes through each
compartment sequentially. The flocculation basin shall have a width of 27.43 m matching the
adjacent sedimentation basin width. Paddle wheels shall have blades with a 150-mm width and a
length of 3.05 m. Outer blades should clear the floor by 305 mm and be 305 mm below the water
surface. Six blades shall be used per paddle wheel with a clear spacing of 305 mm between the
blades. There shall be a clear spacing of 760 to 915 mm between the blades of adjacent paddle
wheels, and an end wall clearance of 305 to 460 mm. Specifically determine:
a. Basin dimensions to nearest 0.01 meters.
b. Optional (zero points): Sketch a preliminary design for the paddle wheels – this is a
much time on it.
c. Power input to the water in each compartment (watts), and the total power (watts).
d. Optional (zero points): Range in rotational speed for each compartment using 1:4
variable speed drives – this is a mechanical engineering drive unit problem, again, if you
decide to give it a try do not spend too much time on it.
Hint: Clearly, for housing circular paddle-wheel mixers, each flocculator compartment should
have a length in the direction of flow that equals the liquid depth, i.e., compartments shall have a
square cross-section in any plane parallel to the fluid velocity
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