20-200 3

Since the flow rate is 1,500 mVday, the required surface area of media is 84,600 nr. Because of the high influent substrate concentration, standard density media (9,300 m:) should be used, requiring 9.10 shafts. Since whole shafts must be used, fO shafts are required.

Given the low flux, it is unlikely that the SOL will be high enough to cause an oxygen limitation, but this can be easily checked by noting point C, the point at which the operating line intersects the ordinate. There it can be seen that the SOL is only 3.5 g BOD5/(nr • day), which is well below the maximum allowable.

b. How large would a multi-stage system have to be?

This analysis is presented in Figure E20.2, which is drawn with an expanded ordinate. The SOL on the initial stage is limited to 32 g BOD.,/(nr ■ day) to

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