FREE WW Wastewater Mathematics Questions and Answers

Question 1

A circular clarifier with a diameter of 80 feet treats a flow of 2.5 MGD. What is the surface overflow rate (SOR) in gpd/ft²?

Accepted Answer

497 gpd/ft²

Answer

31,250 gpd/ft²

Answer

995 gpd/ft²

Answer

1,243 gpd/ft²

Question 2

An aeration basin has a volume of 1.2 million gallons and the MLVSS concentration is 2,800 mg/L. If the plant influent flow is 4.0 MGD with a BOD of 220 mg/L, what is the Food to Microorganism (F/M) ratio?

Accepted Answer

0.26

Answer

0.15

Answer

0.52

Answer

1.20

Question 3

What is the detention time in hours for a sedimentation tank that is 100 feet long, 30 feet wide, and has a water depth of 12 feet, if the flow rate is 3.0 MGD?

Accepted Answer

2.15 hours

Answer

4.31 hours

Answer

1.55 hours

Answer

3.60 hours

Question 4

A pump is delivering 600 GPM against a total dynamic head (TDH) of 50 feet. What is the water horsepower (WHP)?

Accepted Answer

7.58 WHP

Answer

12.12 WHP

Answer

5.05 WHP

Answer

9.45 WHP

Question 5

Calculate the Mean Cell Residence Time (MCRT) in days given the following: Aeration Tank Volume = 2.5 MG, MLSS = 3,000 mg/L, WAS Flow = 0.06 MGD, WAS Conc. = 8,000 mg/L, Effluent TSS = 12 mg/L, and Plant Flow = 5.0 MGD.

Accepted Answer

13.9 days

Answer

8.5 days

Answer

15.6 days

Answer

11.2 days

Question 6

A secondary clarifier receives a flow of 3.5 MGD containing 3,200 mg/L of MLSS. If the clarifier has a diameter of 90 feet, what is the solids loading rate (SLR) in lbs/day/ft²?

Accepted Answer

14.7 lbs/day/ft²

Answer

22.5 lbs/day/ft²

Answer

10.1 lbs/day/ft²

Answer

28.9 lbs/day/ft²

Question 7

An anaerobic digester is fed raw sludge with 72% volatile solids and produces digested sludge with 55% volatile solids. What is the percent volatile solids reduction?

Accepted Answer

52.5%

Answer

23.6%

Answer

61.3%

Answer

48.9%