Civil Engineering PE Water and Wastewater Treatment 5

Question 1

The F/M (food-to-microorganism) ratio in activated sludge is calculated as:

Accepted Answer

Influent BOD load (lb/day) / mass of MLVSS in aeration basin (lb)

Answer

Effluent BOD (mg/L) / MLVSS (mg/L)

Answer

Influent flow (MGD) / sludge wasting rate (MGD)

Answer

MLSS (mg/L) / HRT (days)

Question 2

Phosphorus removal in a biological nutrient removal (BNR) system is achieved by:

Accepted Answer

Alternating anaerobic and aerobic conditions to select for polyphosphate-accumulating organisms (PAOs)

Answer

Nitrification followed by denitrification in anoxic zones

Answer

Adding alum to the anaerobic zone

Answer

Increasing sludge age beyond 20 days

Question 3

A sedimentation basin has a detention time of 4 hours and a flow of 3 MGD. What is the volume of the basin in gallons?

Accepted Answer

500,000 gal

Answer

750,000 gal

Answer

1,000,000 gal

Answer

2,000,000 gal

Question 4

In water treatment, what is the purpose of breakpoint chlorination?

Accepted Answer

To add enough chlorine to oxidize all ammonia-nitrogen and achieve free chlorine residual

Answer

To form chloramines for distribution system residual

Answer

To reduce chlorine to below 0.2 mg/L for taste control

Answer

To lower the pH before coagulation

Question 5

Which of the following best describes the difference between primary and secondary clarifiers in a conventional activated sludge plant?

Accepted Answer

Primary clarifiers remove settleable solids from raw sewage; secondary clarifiers separate biological floc from treated effluent

Answer

Primary clarifiers remove dissolved BOD; secondary clarifiers remove suspended solids only

Answer

Primary clarifiers use chemicals; secondary clarifiers are gravity-only

Answer

Primary clarifiers follow biological treatment; secondary clarifiers precede it

Question 6

What is the typical volatile suspended solids (VSS) to total suspended solids (TSS) ratio for municipal wastewater biosolids, indicating the organic fraction?

Accepted Answer

0.7–0.8

Answer

0.2–0.3

Answer

0.4–0.5

Answer

0.95–1.0

Question 7

The dissolved oxygen (DO) in an aeration basin of an activated sludge system is typically maintained at:

Accepted Answer

1.0–3.0 mg/L

Answer

0.0–0.5 mg/L (anoxic)

Answer

5.0–8.0 mg/L

Answer

10–12 mg/L