hw-18

CENE 599 Sp16 Lecture 19 1

CENE 599 Sp16 Lecture 19 2

Aerated Pond Example Problem Use the data below to design a partial mix aerated pond with three cells of equal volume.

Parameter Value Design flow rate = 3,850 m3/day Influent BOD5 = 310 mg/L Effluent BOD5 = 30 mg/L Reaction rate at 20 oC = 0.204 day-1 Influent temperature oC = 17 oC Summer air temp. oC = Ta = 31 oC Winter air temp. oC = Ta = 11 oC Temperature correction coefficient = 1.03

a. Design for winter conditions. b. Estimate the reaction rate k using Equation 3-5 and a temperature higher

than the winter air temperature, but lower than the influent water temperature.

CENE 599 Sp16 Lecture 19 3

b. Estimate the reaction rate k using Equation 3-5 and a temperature higher than the winter air temperature, but lower than the influent water temperature.

Aerated Pond Design Example

Use T = 14oC as a first trial value.

CENE 599 Sp16 Lecture 19 4

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 5

c. Calculate the total detention time using Equation 3-7. Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 6

d. Calculate the volume of each reactor using the flow rate, number of cells, and detention time.

Aerated Pond Design Example

e. Calculate the surface area of each cell using L:W=3, and a depth of 4.0 m. For this problem, assume the ponds have vertical walls.

CENE 599 Sp16 Lecture 19 7

f. Check the pond temperature using the temperatures provided for this problem, the surface area you just calculated, and Equation 3-6. If this temperature is more than 10% different than your assumed temperature, then use the calculated temperature from Equation 3-6 and start over from Step b above.

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 8

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 9

g. Calculate the effluent from Cell 1 using the equation we derived on Lecture 18 Page 2.

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 10

h. For the second cell, calculate the water temperature (Tw) and rate constant k at that temperature, then calculate the BOD. The volume, surface area, and HRT stay the same for all cells.

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 11

i. For the third cell, make the same calculations using the temperature of the influent water from Cell 2.

Aerated Pond Design Example

j. The concentration is slightly higher than 30 mg/L because of the decreasing k values as temperature decreased in the cells.

CENE 599 Sp16 Lecture 19 12

k. Prepare a summary table showing the volume, length, width, and depth of your ponds and provide a sketch.

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 13

If you set this up as a spreadsheet it is easy to alter the HRT for the cells and adjust the outflow concentration of the last cell to <= 30 mg/L.

Aerated Pond Design Example

CENE 599 Sp16 Lecture 19 14

If you set this up as a spreadsheet it is easy to alter the HRT for the cells and adjust the outflow concentration of the last cell to <= 30 mg/L.

Aerated Pond Design Example