E

I: Influent

PC: Primary clarifiers FC: Final clarifiers E: Effluent

FIG. 7.24.2 Typical arrangements of RBCs. A, Compartmentalization in a single basin using baffles; B, Basins arranged in series.

sulting design equations for a single-stage RBC are as follows:

where:

Q = wastewater flowrate, m3/day Si = influent BOD, mg/l Se = effluent BOD, mg/l

A = required wetted surface area to achieve the required BOD reduction from Si to Se, m2 K = half-velocity constant, mg/l (see Section 7.25) k = maximum BOD removal rate, l/day (see Table 7.25.4)

XA = dry density of the film layer, mg/l S = film layer thickness, m Do = diameter of the disk, m

Di = diameter of the circle that is never submerged (see

Figure 7.24.1), m N = number of disks per stage (compartment)

Environmental engineers can determine both P and Ks by performing a laboratory- or pilot-scale treatability study using the same wastewater. With an equal wetted surface area per stage for an n-stage RBC system, the following equation applies:

The solution of Equation 7.24.5 requires a trial-and-er-ror approach (McGhee 1991). The total wetted surface area required to achieve a given BOD reduction in a multistage RBC system is less than that in a single-stage RBC system.

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