Select an appropriate aerator and aerator configuration for the equalization basin volume calculated in Example 20-6. Assume that the aerators in Table 20-14 are available and that Figure 20-18 applies.

Question

Accepted Answer

a. From Example 20-6, the required storage volume is 1,080 m³ . Using the low end of the recommended range for mixing, estimate the total power required.
Power = (0.004 kW/m³)(1, 080 m³) = 4.32 kW

b. Assume four aerators will be used. Each aerator must supply
[latex]\frac{4.32 kW}{4}= [/latex] 1.08 kW

c. From Table 20-14, the smallest size that will supply enough power is the 1.5 kW aerator. Use this aerator as a first trial.

d. From Table 20-14, the nominal operating depth is 1.8 m. From Figure 20-18, the range of depths for normal operation is from 1.2 to 2.9 m. Use a depth of 2.9 m to estimate the surface area of the equalization basin.

[latex]A = \frac{\sout{V}}{depth}= \frac{1,080 m^{3}}{2.9 m} [/latex] = 372.41 m²

e. Assume a square equalization basin and compute the dimensions.
Length = [latex](372.41 m^{2})^{1/2}[/latex] = 19.30 m

f. Assume each aerator is placed in one quadrant as shown in the sketch below.

g. The diagonal across the equalization basin is the hypotenuse of the triangle formed by the sides. The length of the hypotenuse is
[latex]L_{hypotenuse}= [(19.30)^{2} + (19.30)^{2}]^{1/2}[/latex] = 27.29 m

h. Check the zone of complete mixing. The specified complete mix zone is 8 m for the 1.5 kW aerator. With the aerator placed in the center of the quadrant as shown above, this aerator must completely mix a diameter of
[latex]\frac{24.29 m}{2} =[/latex] 13.64 m

if there are to be no dead spots. Therefore, a larger aerator is required.

i. For another trial, select a 3.5 kW aerator as it has a complete mix zone of 14 m.

j. Check the depth. From Figure 20-18, the depth is satisfactory for the 3.5 kW aerator.

Comments:

1. Multiple aerators are selected to provide redundancy.

2. Alternate solutions that require less power are possible, but power requirements to prevent the deposition of solids may be greater than that required for blending. The actual power supplied from the four large aerators is 0.013 kW/m³ .

3. Because the envelope for complete mixing is fixed by the diagonal, the zone of complete mixing of each aerator will overlap the edges of the basin. This may present erosion problems.

Table 20-14 Selection table for floating mechanical aerators $^{a}$
Size, kW	OTR $^{b}$ , kg/MJ	Nominal operating, depth, m	Complete mix zone, m	Complete O $_{2}$ dispersion zone, m
0.75	0.20	1.8	6	20
1.5	0.23	1.8	8	30
2.5	0.23	1.8	12	45
3.5	0.23	1.8	14	50
5.5	0.22	2.4	15	50
7.5	0.20	3.0	15	55
10	0.21	3.0	19	60
15	0.19	3.0	22	70
20	0.20	3.0	24	80
25	0.21	3.0	26	85
$^{a}$ These aerators are representative but do not represent actual choices. Actual manufacturers’ data must be used for real-world design. $^{b}$ OTR = oxygen transfer rate.

Question 20.7: Select an appropriate aerator and aerator configuration for ...

Related Answered Questions

Determine the equalization basin volume required for the following cyclic flow pattern. Provide a 25% excess capacity for equipment, unexpected flow variations, and solids accumulation. Evaluate the impact of equalization on the mass loading of BOD5 . ...

Verified Answer:

Verified Answer:

Design a screw pumping system for Waterloo’s WWTP that has the following characteristics: Interceptor sewer Minimum sewage elevation = 514.75 m Maximum sewage elevation = 515.00 m Discharge elevation to stilling well = 519.17 m Average flow rate at design capacity = 37,000 m³/d ...

Verified Answer:

Continuing with the headworks design for Waterloo (Example 20-1), design a Parshall flume by specifying the throat width and estimating the maximum depth of the flume. Assume free-flow conditions and 0.6 m freeboard above the maximum depth. ...

Verified Answer:

Estimate the headlosses for a bar rack for Waterloo (Examples 20-1, 20-2, and 20-3) with a clean bar rack and with partial blockage of the screen. Use the following assumptions: 1. Mechanically cleaned bar rack. 2. Bar width = 15 mm. 3. Bar spacing = 20 mm. 4. Angle from vertical = 30°. 5. ...

Verified Answer:

Verified Answer: