Civil Engineering PE Water and Wastewater Treatment 2

Question 1

A water treatment plant uses rapid sand filtration. The design filtration rate is 4 gpm/ft². If the filter box is 20 ft × 30 ft, what is the design flow through this single filter?

Accepted Answer

2,400 gpm

Answer

Flow = rate × area = 4 gpm/ft² × (20 × 30) ft² = 4 × 600 = 2,400 gpm.

Question 2

Which disinfection byproduct (DBP) is primarily formed when chlorine reacts with natural organic matter (NOM) in drinking water?

Accepted Answer

Trihalomethanes (THMs)

Answer

Trihalomethanes (THMs) such as chloroform are the primary DBPs formed when free chlorine reacts with NOM.

Question 3

In a conventional activated sludge system, the sludge volume index (SVI) is 120 mL/g and the MLSS is 3,000 mg/L. What is the settled sludge volume after 30 minutes?

Accepted Answer

360 mL/L

Answer

SVI = (settled volume mL/L × 1,000) / MLSS mg/L, so settled volume = SVI × MLSS / 1,000 = 120 × 3,000 / 1,000 = 360 mL/L.

Question 4

A clarifier has a surface overflow rate of 800 gpd/ft². If the flow is 1.5 MGD, what is the required surface area?

Accepted Answer

1,875 ft²

Answer

Area = Q / SOR = 1,500,000 gpd / 800 gpd/ft² = 1,875 ft².

Question 5

Which of the following best describes the purpose of alkalinity in coagulation during water treatment?

Accepted Answer

It provides bicarbonate/carbonate ions that react with coagulant to form floc

Answer

Alkalinity (bicarbonate/carbonate) reacts with alum or ferric coagulants to form hydroxide floc and release CO₂.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Water and Wastewater Treatment 2