Homework -
Q1. A natural water with a flow of 3800 m3/d is to be treated with an alum dose of 60 mg/L. Determine the chemical feed rate for the alum, the amount of alkalinity consumed by the reaction, and the amount of precipitate produced in mg/L and kg/day.
Q2. A first-stage flocculator uses a six-bladed Rusthon turbine 2 m in diameter rotating at 25 rev/min. What is the Reynolds number? How much power must be applied to the shaft to rotate it? What flow does the impeller pump?
Q3. The impeller in Q2 is in a tank 4 m square and 4 m deep. Calculate the tank turnover time and G values.
Q4. Design a flocculation compartment for a horizontal-shaft flocculator with two paddles like that. How fast must the paddle wheel rotate in that compartment to generate a G value of 30 s-1?
Q5. For the rectangular horizontal-flow sedimentation basin and influent particle-settling characteristics given (use data set A), calculate the particle removal efficiency and plot the influent and effluent particle concentrations as a function of particle size.
|
Parameter
|
A
|
|
Flow rate, m3/d
|
7,570
|
|
Length, m
|
30
|
|
Width, m
|
5
|
|
Settling Velocity, m/h
|
A
|
|
0-0.4
|
511
|
|
0.4-0.8
|
657
|
|
0.8-1.2
|
876
|
|
1.2-1.6
|
1168
|
|
1.6-2.0
|
1460
|
|
2.0-2.4
|
1314
|
|
2.4-2.8
|
657
|
|
2.8-3.2
|
438
|
|
3.2-3.6
|
292
|
|
3.6-4.0
|
292
|
|
Total
|
7665
|
Q6. Determine the area of a clarifier required for solids thickening for the parameters given below (use data set A). The settling velocity of the sludge blanket follows the data given in Table and plotted on Fig. Also determine JL, CL, and Qu.
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Parameter
|
A
|
|
Influent flow rate, m3/h
|
3,000
|
|
Influent solids conc., mg/L
|
500
|
|
Underflow solids conc., mg/L
|
10,000
|
Q7. A filter is designed with the following specifications. The anthracite and sand have density of 1700 and 2650 kg/m3, respectively, and the design temperature is 10 C. For a given sample (use data set C), calculate the clean-bed head loss.
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Item
|
C
|
|
Bed type
|
Dual media
|
|
Filtration rate (m/h)
|
15
|
|
Anthracite specifications:
|
|
|
Effective size (mm)
|
1.0
|
|
Depth (m)
|
1.5
|
|
Sand specifications:
|
|
|
Effective size (mm)
|
0.5
|
|
Depth (m)
|
0.3
|
Q8. Given a backwash flow rate of 45 m/h and temperature of 20 C, calculate the largest (a) sand particle (density = 2650 kg/m3) and (b) floc solid particle (density = 1050 kg/m3) that can be washed from a filter bed.
Note: Questions are from Crittenden et al., MWH Water Treatment Fundamentals and Design 3/e.