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

Stalked ciliates and rotifers are higher life-form microorganisms that are indicators of a stable and mature activated sludge process. Their presence signifies a well-established food web, low BOD, and sufficient aging of the sludge (high Mean Cell Residence Time), which typically results in good floc formation, excellent settling, and a clear final effluent.

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

The fundamental difference lies in how the biomass is maintained. Trickling filters are an "attached growth" system where microorganisms form a slime layer (biofilm) on a fixed media (like rocks or plastic). In contrast, the activated sludge process is a "suspended growth" system where microorganisms are kept in suspension in an aeration tank.

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

Biological nitrogen removal is a two-step process. First, nitrification occurs in an aerobic (oxygen-rich) environment where bacteria like Nitrosomonas and Nitrobacter convert ammonia to nitrate. Second, denitrification occurs in an anoxic (low oxygen, but nitrate is present) environment where different bacteria convert the nitrate to nitrogen gas, which is then released into the atmosphere.

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

Filamentous bulking is a common operational problem where the excessive growth of filamentous bacteria creates a web-like structure within the flocs. This structure prevents the flocs from compacting and settling properly in the clarifier, leading to a high sludge volume index (SVI) and potential solids washout.

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

While bacteria are the primary decomposers, protozoa play a crucial role as predators. They consume dispersed, free-swimming bacteria, which helps in several ways: it clarifies the effluent by removing turbidity, encourages the remaining bacteria to form larger, settleable flocs, and helps control the overall bacterial population.

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Practice Test

Wastewater Operator Secondary Treatment and Microbiology Questions and Answers