Wastewater Operator Secondary Treatment and Microbiology Questions and Answers

Question 1

An operator observes a large population of stalked ciliates and rotifers during a microscopic examination of activated sludge. What does this MOST likely indicate about the treatment process?

Accepted Answer

A stable, mature sludge with a good settling quality and low effluent turbidity.

Answer

A recent toxic shock load has occurred.

Answer

The system has a high food-to-microorganism (F/M) ratio.

Answer

The dissolved oxygen level in the aeration basin is critically low.

Question 2

Which of the following is a key difference between the activated sludge process and a trickling filter?

Accepted Answer

In a trickling filter, microorganisms grow on a media surface, whereas in activated sludge, they are suspended in the mixed liquor.

Answer

Activated sludge is an anaerobic process, while trickling filters are aerobic.

Answer

Trickling filters use a suspended growth of microorganisms, while activated sludge uses attached growth.

Answer

Activated sludge processes typically require less operational control and skill.

Question 3

A wastewater treatment plant is required to remove nitrogen from its effluent. This is typically achieved through the biological processes of nitrification and denitrification. Which sequence and environmental condition is correct for this removal process?

Accepted Answer

Nitrification in an aerobic zone, followed by denitrification in an anoxic zone.

Answer

Denitrification in an anoxic zone, followed by nitrification in an aerobic zone.

Answer

Nitrification in an anoxic zone, followed by denitrification in an aerobic zone.

Answer

Denitrification in an aerobic zone, followed by nitrification in an anaerobic zone.

Question 4

An operator is troubleshooting an activated sludge system experiencing "bulking sludge," which is settling very poorly in the secondary clarifier. What is a common microbiological cause of this condition?

Accepted Answer

Proliferation of filamentous bacteria that interfere with floc compaction.

Answer

Excessive growth of amoebas and flagellates.

Answer

Over-predation by rotifers and nematodes.

Answer

A lack of floc-forming bacteria in the mixed liquor.

Question 5

In the context of secondary treatment, what is the primary role of protozoa?

Accepted Answer

To consume free-swimming bacteria, promoting floc formation and clarifying the effluent.

Answer

To convert ammonia directly into nitrogen gas.

Answer

To consume organic waste through anaerobic digestion.

Answer

To act as the primary decomposers of complex organic molecules.

Question 6

The conversion of ammonia (NH4+) to nitrite (NO2-) is the first step in nitrification. Which group of bacteria is primarily responsible for this specific conversion under aerobic conditions?

Accepted Answer

Nitrosomonas

Answer

Nitrobacter

Answer

Pseudomonas

Answer

Zoogloea

An operator observes a large population of stalked ciliates and rotifers during a microscopic examination of activated sludge.What does this MOST likely indicate about the treatment process?

An operator observes a large population of stalked ciliates and rotifers during a microscopic examination of activated sludge.
What does this MOST likely indicate about the treatment process?