Page 418 - Water and wastewater engineering

SEDIMENTATION 10-35

Operation and Maintenance. To facilitate maintenance, modules must be sufficiently inde-
pendent to allow removal of individual units. An overhead crane must be provided. Stainless
steel modules are preferred.

High-Rate Settler Module Design Criteria
Typical design criteria for horizontal-flow rectangular sedimentation basins are summarized in
Table 10-6 . Example 10-5 illustrates the design of a high-rate settler in a rectangular sedimentation
basin.

TABLE 10-6
Typical design criteria for high-rate settler modules

Parameter Typical range of values Comment
Inlet zone
Distance to diffuser 2 m
Diffuser hole diameter 0.10–0.20 m
Settling zone
3 2
Overflow rate 60–180 m /d · m Alum floc
Side water depth (SWD) 3–5 m
Length 60 m Chain-and-flight
Width 0.3 m increments Chain-and-flight
6 m maximum per train Chain-and-flight
24 m maximum 3 trains per drive Chain-and-flight
Settler
Fraction of basin covered < 0.75 For plates 0.95
Height 0.5–2.0 m For plates 1.0 m
Plate angle 55
Tube angle 60
Tube hydraulic diameter 0.05–0.08 m
Tube velocity 0.0025–0.0033 m/s
Approach velocity 0.010 m/s Horizontal, mean
Reynolds number < 50
Froude number > 10 5
Outlet zone
Launder length Equal to length of settler
Launder spacing 1.5 m on centers
Launder elevation 0.6–1.0 m above top of settler For plates to top
3
Launder weir loading < 300 m /d · m
Sludge zone
Depth 0.6–1 m Equipment dependent
Slope 1:600 Mechanical cleaning
Sludge collector speed 0.3–0.9 m/min
Sources: Kawamura, 2000, MWH, 2005, Willis, 2005.