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Sample Problem. A town has been directed to upgrade its WWTP which can meet

an effluent standard of 30.0

BOD5 and 30.0

suspended solids (SS). Thetechnology selected was completely mixed activated sludge system.

Assuming that the BOD5 of the SS may be estimated as equal to 63% of the

SS concentration, estimate the required volume of the aeration tank. The ff data are

available from the existing plant:

Assume the following values for the growth constants: Ks=100

;

.Solution:

Assuming that the clarifier can produce an effluent with only 30.0

SS, we canestimate the allowable soluble in the effluent using the 63% assumption fromthe above and equation 10.

can be estimated with equation 9,

For the detention time, assuming a value of 2,000

for the MLVSS and equation11,

By equation 6, volume may be estimated as,

Sample Problem. Compute the F/M ratio for the plant from the preceding problem.

Solution:

Using data from the preceding problem and equation 12,

( )

Sample Problem. Considering the same conditions from the preceding problems, wenow wish to consider the return sludge design and given the ff data:

Design Data:

Solution:

From Figure 4. Given MLSS and temp, we can select SVI = 175

Using equation 17,

From equation 7,

From equation 14 and 16, respectively,

Which can be validated by using Figure 3

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Sample Problem. A lagoon having 3 cells, each 115,000 m2, a minimum operating

depth of 0.6 m and a maximum operating depth of 1.5 m, receives 1,900

of WW

having an average BOD5 of 122 . What is the BOD5 loading and what is thedetention time?

Solution:

(

)(

)

( )

Detention time working volume between the minimum and maximum operating

levels divided by the average flow

Sample Problem. If a wastewater has a soluble orthophosphate concentration of

4.00

as P, what theoretical amount of ferric chloride will be required to remove itcompletely?

Solution:

From the equation, one mole of ferric chloride is required for each mole of

phosphorous to be removed. The pertinent gram molecular weight are as follow: With a PO4-P of 4.00

, the theoretical amount of ferric chloride would be

Because of side reactions, solubility product limitations, and day-to-day variations,

the actual amount of chemical to be used must be determined by jar tests on the

wastewater. You can expect that the actual ferric chloride dose will be 1.5 to 3 times

the theoretically calculated amount. Likewise, the amount of alum dose will be 1.25to 2.5 times the theoretical amount.