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Wastewater Math Concepts Book 2

Intermediate Level Problems

Table of Contents

Page

Flow Problems 1

Grit Channel Problems 4

Sedimentation Basin, Tank, and Clarifier Problems

Detention Time 10

Surface Loading Rate 12

Weir Overflow Rate 15

Solids Loading 18

Trickling Filter Problems

Hydraulic Loading 21

Organic Loading 24

Removal Efficiency 27

Rotating Biological Contactors


Organic Loading 33

Activated Sludge Problems

Sludge Volume Index (SVI) 36

Pounds of Solids in Aeration Basin 39

Pounds of BOD Applied to Aeration Basin 42

Sludge Age 45

Pond Problems

Detention Time 48

Population Loading 51


Organic Loading 57

Chlorination Problems

Residual 60

Chlorinator Setting 62

Chemical Dose Problems

Polymer dose 64

Feed Pump Calibration and Setting 72

Blueprints 80

Final Exam 84

EQUIVALENTS AND FORMULAS

EQUIVALENTS 1 acre = 43,560 square feet

1 cubic foot of water = 7.48 gallons 1 gallon of water = 8.34

pounds

1 day = 1,440 minutes = 86,400 seconds

1 million gallons/day = 694 gallons/minute = 1.547 cubic feet/second = 3.069 acre-feet/day

1% = l0,000 mg/L π = 3.14

1 inch of mercury = 1.133 feet of water 1 pound/square inch = 2.31 feet of

water

I HP = 0.746 Kw = 550 ft-lb/sec = 33,000 ft-lb/min

FORMULAS Area of rectangle = Length x Width

Area of circle = π x Diameter2 = 0.785 x Diameter

2

4

Volume of rectangular or circular tank with uniform depth = Area x Depth

Volume of cone = 1/3 x Base Area x Depth

Circumference = π x Diameter

Velocity = Distance Flow = Velocity x Area

Time

Detention time = Volume

Flow

Pounds/day = 8.34 x Flow, mgd x Concentration, mg/L

F/M = Pounds of BOD or COD applied per day

Pounds of MLVSS under aeration

MCRT = Pounds of MLSS in secondary system (aeration tank + clarifier)

Pounds of MLSS leaving secondary system per day (effluent + WAS)

Water HP = Flow, gpm x Total Head, ft

3960 gpm-ft

HP

Brake HP = Power to electric motor x Motor efficiency

Volatile Solids Reduction, % = In – Out x 100%

In - (In x Out)

1

Flow Problems

Convert between gpm and MGD:

1. 850 gpm = _____________ MGD

2. 1200 gpm = _____________ MGD

3. 775 gpm = _____________ MGD

4. 350 gpm = _____________ MGD

5. 1150 gpm = _____________ MGD

6. 1525 gpm = _____________ MGD

2

Convert between MGD and CFS:

7. 2.3 MGD = _____________ CFS

8. 8.5 MGD = _____________ CFS

9. 17 MGD = _____________ CFS

10. 4.3 MGD = _____________ CFS

11. 9.7 MGD = _____________ CFS

12. 3.2 MGD = _____________ CFS

Grit Channel Problems

3


1. Estimate the velocity in feet/second of wastewater flowing through a grit channel

if a stick travels 18 feet in 43 seconds.



4


if a stick travels 120 feet in 2 minutes.




5




if a stick travels 30 feet in 1 minute.

6

7. A grit channel removed 2.9 cubic feet of grit during a 24 hour period when total

flow was 0.7 MGD. How many cubic feet of grit are removed per million

gallons?

8. A grit channel removed 4 cubic feet of grit during a 24 hour period when total


gallons?


7



gallons?


flow was 10 MGD. How many cubic feet of grit are removed per million gallons?

8



gallons?


flow was 1 MGD. How many cubic feet of grit are removed per million gallons?

Clarifier Problems

9

Clarifier Problems

Detention time

1. A round clarifier handles a flow of 1 MGD and suspended solids of 3,400 mg/L.

The clarifier is 52 feet in diameter and has a depth of 8 feet. Find the clarifier

detention time in hours.

2. A round clarifier handles a flow of 2.9 MGD and suspended solids of 3,400 mg/L.



10

3. A round clarifier handles a flow of 0.75 MGD and suspended solids of 3,200

mg/L. The clarifier is 48 feet in diameter and has a depth of 10 feet. Find the

clarifier detention time in hours.




Clarifier Problems

11




Surface Loading Rate


The clarifier is 52 feet in diameter and has a depth of 8 feet. Find the surface

loading rate in GPD/ft2.

12







Clarifier Problems

13







14

Weir Overflow Rate


The clarifier is 52 feet in diameter and has a depth of 8 feet. What is the weir

overflow rate?




Clarifier Problems

15



overflow rate?



overflow rate?

16



overflow rate?



overflow rate?

Clarifier Problems

17

Solids Loading


The clarifier is 52 feet in diameter and has a depth of 8 feet. Find the solids

loading in this clarifier in lb/day/sq. ft.




18



solids loading in this clarifier in lb/day/sq. ft.




Clarifier Problems

19



solids loading in this clarifier in lb/day/sq. ft.




20


Hydraulic loading

1. A flow of 1.5 MGD is applied to a trickling filter with a 48 foot diameter and 5

foot depth. The incoming BOD is 130 mg/L. Calculate the Hydraulic loading on

the filter in gpd/ft2.

2. A flow of 5 MGD is applied to a trickling filter with a 60 foot diameter and 10


the filter in gpd/ft2

.


21

3. A flow of 3 MGD is applied to a trickling filter with a 55 foot diameter and 6 foot

depth. The incoming BOD is 140 mg/L. Calculate the Hydraulic loading on the

filter in gpd/ft2.

4. A flow of 2.5MGD is applied to a trickling filter with a 44 foot diameter and 8



22






the filter in gpd/ft2

.


23

Organic Loading


foot depth. The incoming BOD is 130 mg/L. Calculate the Organic loading on

the filter in lb/day/1,000 ft3 of media.

2. A flow of 5 MGD is applied to a trickling filter with a 60 foot diameter and 10



24

3. A flow of 3 MGD is applied to a trickling filter with a 55 foot diameter and 6 foot

depth. The incoming BOD is 140 mg/L. Calculate the Organic loading on the

filter in lb/day/1,000 ft3 of media.

4. A flow of 2.5MGD is applied to a trickling filter with a 44 foot diameter and 8




25







26

Removal Efficiency

1. The influent BOD of a trickling filter is 260 mg/L and the effluent BOD is 20

mg/L. What is the removal efficiency of this trickling filter?




27





28





RBC Problems

29

RBC Problems

Hydraulic Loading

1. A rotating biological contactor treats a flow of 1.2 MGD. The surface area of the

contactor is 350,000 square feet. The influent BOD is 180 mg/L and the

suspended solids is 200 mg/L. Assume a K value of 0.5 to calculate soluble

BOD. Find the hydraulic loading in gpd/ft2.





30

3. A rotating biological contactor treats a flow of 4 MGD. The surface area of the








RBC Problems

31









32

Organic Loading




BOD. Calculate the Organic loading in lb/day/1,000ft2 of media surface.





RBC Problems

33









34










35


Sludge Volume Index (SVI)

1. Lab results for a WWTP are listed below. Aeration tank volume is 0.4 MG.

MLSS 1600 mg/L

Mixed liquor volatile content 76%

Primary effluent BOD 130 mg/L

Primary effluent suspended solids 100 mg/L

Plant flow 2.1 MGD

30 minute Settleable Solids 190 ml/L

What is the Sludge Volume Index?

2. Lab results for a WWTP are listed below. Aeration tank volume is 1 MG.

MLSS 1800 mg/L




Plant flow 4 MGD



36


MLSS 1700 mg/L




Plant flow 6 MGD




MLSS 2000 mg/L




Plant flow 5.5 MGD




37


MLSS 1600 mg/L




Plant flow 2.1 MGD




MLSS 1700 mg/L




Plant flow 7.2 MGD



38

Pounds of Solids in Aeration Basin


MLSS 1600 mg/L




Plant flow 2.1 MGD

How many pounds of solids are in the aeration basin?


MLSS 1800 mg/L




Plant flow 4 MGD



39


MLSS 1700 mg/L




Plant flow 6 MGD



MLSS 2000 mg/L




Plant flow 5.5 MGD


40


MLSS 1600 mg/L




Plant flow 2.1 MGD



MLSS 1700 mg/L




Plant flow 7.2 MGD



41

Pounds of BOD Applied to the Aeration Basin Each Day


MLSS 1600 mg/L




Plant flow 2.1 MGD

Calculate the lb/day of BOD applied to the aeration basin.


MLSS 1800 mg/L




Plant flow 4 MGD


42


MLSS 1700 mg/L




Plant flow 6 MGD



MLSS 2000 mg/L




Plant flow 5.5 MGD



43


MLSS 1600 mg/L




Plant flow 2.1 MGD



MLSS 1700 mg/L




Plant flow 7.2 MGD


44

Sludge Age


MLSS 1600 mg/L




Plant flow 2.1 MGD

Calculate the sludge age in days.


MLSS 1800 mg/L




Plant flow 4 MGD



45


MLSS 1700 mg/L




Plant flow 6 MGD



MLSS 2000 mg/L




Plant flow 5.5 MGD


46


MLSS 1600 mg/L




Plant flow 2.1 MGD



MLSS 1700 mg/L




Plant flow 7.2 MGD


Pond Problems

47

Pond Problems

Detention Time

1. The treatment pond is 4 feet deep and has an average length of 500 feet.

The average width is 350 feet. Flow through the pond is 0.4 MGD. BOD

in the pond is 120 mg/L. The treatment pond services 4,500 people.

Calculate the detention time in days.


The average width is 300 feet. Flow through the pond is 0.45 MGD.

BOD in the pond is 130 mg/L. The treatment pond services 4,000 people.


48





4. The treatment pond is 4.5 feet deep and has an average length of 700 feet.




Pond Problems

49









50

Population Loading




Calculate the population loading in persons/acre.





Pond Problems

51









52









Pond Problems

53

Hydraulic loading




Calculate the hydraulic loading in inches per day.





54









Pond Problems

55









56

Organic Loading




Calculate the organic loading on the pond in lb BOD/day/acre.





Pond Problems

57









58









Disinfection Problems

59


Residual

1. Find the chlorine demand of an effluent if the chlorine dose is 8.6 mg/L and the

residual is 1.3 mg/L





60








61

Chlorinator Setting (lb/day)

1. In order to maintain a satisfactory chlorine residual, the chlorine dose must be at 9

mg/L when flow is 0.4 MGD. Find the chlorinator setting in lb/day.



3. In order to maintain a satisfactory chlorine residual, the chlorine dose must be at

7.5 mg/L when flow is 0.8 MGD. Find the chlorinator setting in lb/day.

62

4. In order to maintain a satisfactory chlorine residual, the chlorine dose must be at

10 mg/L when flow is 0.9 MGD. Find the chlorinator setting in lb/day.






63


Polymer dose

1. The optimum polymer dose as shown by a jar test is 11 mg/L. Determine the

setting on the liquid polymer chemical feeder in ml/minute when plant flow is 5

MGD. The liquid polymer delivered to the plant contains 640 mg/ml of liquid

solution.




solution.

64




solution.


setting on the liquid polymer chemical feeder in ml/minute when plant flow is 2.2


solution.


65

5. The optimum polymer dose as shown by a jar test is 8.8 mg/L. Determine the



solution.




solution.

66


setting on the liquid polymer chemical feeder in gallons/day when plant flow is 5

MGD. The liquid polymer delivered to the plant contains 5.3 pounds per gallon

of liquid polymer solution.






67






setting on the liquid polymer chemical feeder in gallons/day when plant flow is

3.5 MGD. The liquid polymer delivered to the plant contains 5.5 pounds per

gallon of liquid polymer solution.

68










69

13. Find the chemical feed in lb/day of polymer from a chemical feed pump. The

polymer solution is 1.4 % (14,000 mg/L). Assume that the specific gravity of the

polymer solution is 1.0. During a pump catch, the feed pump delivered 850 ml

over a 5 minute period.



polymer solution is 1.0. During a pump catch, the feed pump delivered 1,200 ml


70







polymer solution is 1.0. During a pump catch, the feed pump delivered 1,000 ml



71

Chemical Feed Pump Calibration and Setting

1. Determine the actual chemical feed in lb/day from a dry chemical feeder. A

bucket placed under the chemical feeder weighs 0.25 lb empty. After 30 minutes,

the bucket and the chemical weigh 2.3 lb.




72








73

5. A chemical feed pump lowered the chemical tank level 1 foot, 4 inches over an 8

hour shift. The tank is round with a 3 foot diameter. Find the feed rate in gallons

per minute and gallons per day.

6. A chemical feed pump lowered the chemical tank level 2 feet over an 8 hour shift.

The tank is round with a 4 foot diameter. Find the feed rate in gallons per minute

and gallons per day.

74

7. A chemical feed pump lowered the chemical tank level 3 feet, 6 inches over a 10

hour shift. The tank is round with a 4.5 foot diameter. Find the feed rate in

gallons per minute and gallons per day.

8. A chemical feed pump lowered the chemical tank level 3 feet over a 24 hour

period. The tank is round with a 3 foot diameter. Find the feed rate in gallons per

minute and gallons per day.


75


hour shift. The tank is a cube with a length and width of 4 feet. Find the feed rate

in gallons per minute and gallons per day.

10. A chemical feed pump lowered the chemical tank level 1 foot, 6 inches over a 4

hour period. The tank is a 5 foot cube. Find the feed rate in gallons per minute

and gallons per day.

76

11. Determine the setting in percent stroke on a chemical feed pump to deliver 3.0

mg/L of polymer. The flow is 450 gpm. The polymer strength is 4.5%. The

pump has a maximum capacity of 90 gallons per day at a setting of 100%

capacity.




capacity.


77



pump has a maximum capacity of 100gallons per day at a setting of 100%

capacity.




capacity.

78




capacity.




capacity.

Blueprint Problems

79

Blueprints

1. A set of blueprints for a treatment plant has a scale of ¼ inch = 1 foot. On the

prints, the primary clarifier measures 8 ¾ inches by 15 ½ inches. What is the

surface area of the clarifier in square feet?




80







Blueprint Problems

81

5. The blueprints for a treatment plant are ¼ inch = 1 foot scale. Find the volume in

gallons of a round chemical storage tank that measure 3 inches in diameter and 2

inches tall on the blueprints.




82







Final Exam

83

Final Exam

1. 635 gpm = _____________ MGD

a. 2.135 MGD

b. 0.850 MGD

c. 1.213 MGD

d. 0.914 MGD

2. 1.34 MGD = _____________ CFS

a. 0.5 CFS

b. 2.1 CFS

c. 1.8 CFS

d. 3.2 CFS



a. 96%

b. 93%

c. 91%

d. 89%


84

MLSS 1800 mg/L




Plant flow 10 MGD


a. 6,000 lb

b. 5,000 lb

c. 7,000 lb

d. 2,000 lb



a. 4.3 mg/L

b. 2.3 mg/L

c. 6.2 mg/L

d. 9.8 mg/L



Final Exam

85

a. 135 lb/day

b. 113 lb/day

c. 121 lb/day

d. 100 lb/day



a. 0.4 ft/sec

b. 0.6 ft/sec

c. 0.7 ft/sec

d. 1.4 ft/sec

86

8. A grit channel removed 5 cubic feet of grit during a 24 hour period when total


gallons?

a. 6.25 ft3/MG

b. 7.25 ft3/MG

c. 5.25 ft3/MG

d. 4.25 ft3/MG



overflow rate?

a. 22,562 gpd/ft

b. 4,750 gpd/ft

c. 58,917 gpd/ft

d. 42,615 gpd/ft

Final Exam

87




a. 1,433 gpd/ft2

b. 1,230 gpd/ft2

c. 1,610 gpd/ft2

d. 2,763 gpd/ft2





a. 3.6 gpd/ft2

b. 5.2 gpd/ft2

c. 4.4 gpd/ft2

d. 6.4 gpd/ft2

88





a. 4.2 lb/day/1,000ft2

b. 5.1 lb/day/1,000ft2

c. 1.5 lb/day/1,000ft2

d. 2.3 lb/day/1,000ft2


MLSS 1500 mg/L




Plant flow 4.3 MGD



a. 96

b. 116

c. 133

d. 124

Final Exam

89


MLSS 1600 mg/L




Plant flow 2.6 MGD


a. 5,250 lb/day

b. 3,250 lb/day

c. 2,250 lb/day

d. 4,250 lb/day


MLSS 1500 mg/L




Plant flow 3.2 MGD


a. 0.5 days

b. 2.3 days

c. 3.1 days

d. 1.9 days

90

16. The treatment pond is 5 feet deep and has an average length of 400 feet. The

average width is 300 feet. Flow through the pond is 0.6 MGD. BOD in the pond

is 130 mg/L. The treatment pond services 4,800 people. Calculate the detention

time in days.

a. 1.2 days

b. 7.5 days

c. 6.4 days

d. 3.5 days


average width is 375 feet. Flow through the pond is 1 MGD. BOD in the

pond is 120 mg/L. The treatment pond services 6,000 people. Calculate the

population loading in persons/acre.

a. 1,463 persons/acre

b. 1,221 persons/acre

c. 1,565 persons/acre

d. 1,318 persons/acre

Final Exam

91


average width is 450 feet. Flow through the pond is 1.4 MGD. BOD in the pond

is 110 mg/L. The treatment pond services 7,500 people. Calculate the hydraulic

loading in inches per day.

a. 9.5 in/day

b. 8.8 in/day

c. 7.2 in/day

d. 4.8 in/day


average width is 390 feet. Flow through the pond is 0.55 MGD. BOD in the

pond is 120 mg/L. The treatment pond services 5,500 people. Calculate the

organic loading on the pond in lb BOD/day/acre.

a. 23 lb BOD/day/acre

b. 54 lb BOD/day/acre

c. 46 lb BOD/day/acre

d. 96 lb BOD/day/acre

92




solution.

a. 425 ml/min

b. 395 ml/min

c. 260 ml/min

d. 140 ml/min





a. 142 gpd

b. 157 gpd

c. 137 gpd

d. 162 gpd

Final Exam

93





a. 10 lb/day

b. 11 lb/day

c. 15 lb/day

d. 16 lb/day




a. 312 lb/day

b. 112 lb/day

c. 172 lb/day

d. 212 lb/day

94


hour shift. The tank is round with a 4 foot diameter. Find the feed rate in gallons

per minute and gallons per day.

a. 0.34 gpm, 494 gpd

b. 0.25 gpm, 360 gpd

c. 0.55 gpm, 792 gpd

d. 0.75 gpm, 999 gpd




a. 562 lb/day/1,000ft3

b. 450 lb/day/1,000ft3

c. 373 lb/day/1,000ft3

d. 674 lb/day/1,000ft3

Final Exam

95




a. 34 lb/day/ft2

b. 39 lb/day/ft2

c. 41 lb/day/ft2

d. 29 lb/day/ft2




capacity.

a. 40%

b. 70%

c. 80%

d. 20%

96




a. 1,895 gpd/ft2

b. 1,575 gpd/ft2

c. 1,430 gpd/ft2

d. 1,835 gpd/ft2

Answer Key

97

Flow Problems Grit Channel Problems

1. 1.2 MGD 1. 0.4 ft/sec

2. 1.7 MGD 2. 2 ft/sec

3. 1.1 MGD 3. 1 ft/sec

4. 0.5 MGD 4. 1.7 ft/sec

5. 1.66 MGD 5. 4.3 ft/sec

6. 2.2 MGD 6. 0.5 ft/sec

7. 3.6 CFS 7. 4.1 ft3/MG

8. 13.1 CFS 8. 2.2 ft3/MG

9. 26.3 CFS 9. 1.9 ft3/MG

10. 6.7 CFS 10. 0.45 ft3/MG

11. 15 CFS 11. 4 ft3/MG

12. 5 CFS 12. 1.6 ft3/MG

98

Clarifier Problems Trickling Filter Problems

1. 3 hr 1. 829 gpd/ft2

2. 2.1 hr 2. 1,769 gpd/ft2

3. 4.3 hr 3. 1,263 gpd/ft2

4. .7 hr 4. 1,645 gpd/ft2

5. 0.9 hr 5. 3,594 gpd/ft2

6. 471 gpd/ft2 6. 917 gpd/ft

2

7. 1,887 gpd/ft2 7. 180 lb/day/1000ft

3

8. 3,110 gpd/ft2 8. 192 lb/day/1000ft

3

9. 7,962 gpd/ft2 9. 246 lb/day/1000ft

3

10. 2,548 gpd/ft2 10. 214 lb/day/1000ft

3

11. 6,124 gpd/ft 11. 809 lb/day/1000ft3

12. 54,140 gpd/ft 12. 199 lb/day/1000ft3

13. 7,962 gpd/ft 13. 92%

14. 22,293 gpd/ft 14. 92%

15. 35,386 gpd/ft 15. 88%

16. 42,849 gpd/ft 16. 91%

17. 13.4 lb/day/ft2 17. 96%

18. 41.9 lb/day/ft2 18. 95%

19. 11.1 lb/day/ft2

20. 126 lb/day/ft2

21. 90.3 lb/day/ft2

22. 114 lb/day/ft2

Answer Key

99

RBC Problems Activated Sludge Problems

1. 3.4 gpd/ft2 1. 119 13. 2,277 lb/day

2. 3.1 gpd/ft2 2. 100 14. 4,670 lb/day

3. 5 gpd/ft2 3. 100 15. 6,005 lb/day

4. 7.4 gpd/ft2 4. 95 16. 5,963 lb/day

5. 5 gpd/ft2 5. 100 17. 2,452 lb/day

6. 2.5 gpd/ft2 6. 124 18. 9,007 lb/day

7. 2.3 lb/day/1000ft2 7. 5,338 lb 19. 3 days

8. 2.1 lb/day/1000ft2 8. 15,012 lb 20. 4 days

9. 2.9 lb/day/1000ft2 9. 19,849 lb 21. 4 days

10. 5.3 lb/day/1000ft2 10. 25,020 lb 22. 4.5 days

11. 2.7 lb/day/1000ft2 11. 6,672 lb 23. 3.5 days

12. 1.9 lb/day/1000ft2 12. 22,685 lb 24. 3 days

100

Pond Problems

1. 13 days

2. 10 days

3. 15 days

4. 16.5 days

5. 13 days

6. 13 days

7. 1,452 persons/acre






13. 3.7 in/day

14. 6 in/day

15. 4.8 in/day

16. 3.3 in/day

17. 4.5 in/day

18. 3.6 in/day

19. 100 lb/day/acre

20. 177 lb/day/acre

21. 151 lb/day/acre

22. 89 lb/day/acre

23. 134 lb/day/acre

24. 99 lb/day/acre


1. 7.3 mg/L

2. 7.7 mg/L

3. 6.8 mg/L

4. 6.2 mg/L

5. 5.5 mg/L

6. 9.3 mg/L

7. 30 lb/day

8. 33.4 lb/day

9. 50 lb/day

10. 75 lb/day

11. 81.7 lb/day

12. 50 lb/day


Answer Key

101

1. 226 ml/min

2. 334 ml/min

3. 583 ml/min

4. 86.8 ml/min

5. 127 ml/min

6. 84 ml/min

7. 86.5 gal/day

8. 122.5 gal/day

9. 80.5 gal/day

10. 90.2 gal/day

11. 108.4 gal/day

12. 233 gal/day

13. 7.5 lb/day

14. 15.2 lb/day

15. 9 lb/day

16. 7.4 lb/day

17. 98.4 lb/day

18. 120 lb/day

19. 183.6 lb/day

20. 128.4 lb/day

21. .146 gpm

210.9 gpd

22. .391 gpm

563.7 gpd

23. .694 gpm

99.8 gpd

24. .110 gpm

158.5 gpd

25. .332 gpm

477.5 gpd

26. 1.17 gpm

1,683 gpd

27. 48%

28. 34.4%

29. 55.5%

30. 33.3%

31. 53.2%

32. 47%

Blueprints

102

1. 2,170 ft2

2. 1,950 ft2

3. 1,566 ft2

4. 2,046 ft2

5. V = 6,764 gal

6. 18,038 gal

7. 46,974 gal

8. 65,764 gal

Final Exam

1. d. 0.914 MGD

2. b. 2.1 CFS

3. b. 93 %

Answer Key

103

4. a. 6,000 lb

5. c. 6.2 mg/L

6. b. 113 lb/day

7. c. 0.7 ft/sec

8. a. 6.25 ft3/MG

9. c. 58,917 gpd/ft

10. a. 1,433 gpd/ft2

11. d. 6.4 gpd/ft2

12. a. 4.2 lb/day/1,000ft2

13. c. 133

14. b. 3,250 lb/day

15. d. 1.9 days

16. b. 7.5 days

17. a. 1452 persons/acre

18. c. 7.2 in/day

19. d. 96 lb BOD/day/acre

20. b. 395 ml/min

21. a. 142 gpd

22. a. 10 lb/day

23. d. 212 lb/day

24. a. 0.34 gpm, 493 gpd

25. d. 674 lb/day/1,000ft3

26. b. 39 lb/day/ft2

27. b. 70 %

28. d. 1,835 gpd/ft

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