Wastewater Operator Biological Treatment Processes Questions and Answers

Question 1

An operator at an activated sludge plant notices the sludge in the secondary clarifier is settling poorly, has a high Sludge Volume Index (SVI), and appears light and fluffy.
Microscopic examination reveals an excessive growth of long, thread-like bacteria.
Which of the following is the MOST likely cause of this condition, known as filamentous bulking?

Accepted Answer

Low Food-to-Microorganism (F/M) ratio and low dissolved oxygen.

Answer

High Mean Cell Residence Time (MCRT) and high pH.

Answer

High wasting rates and excessive aeration.

Answer

Low influent Biochemical Oxygen Demand (BOD) and high alkalinity.

Question 2

Which of the following conditions is essential for the denitrification process to occur effectively in an anoxic zone?

Accepted Answer

Presence of nitrate, an absence of free oxygen, and a sufficient carbon source.

Answer

High dissolved oxygen (DO) and a readily available carbon source.

Answer

Low pH, high temperature, and the presence of ammonia.

Answer

High alkalinity, presence of nitrites, and vigorous mixing.

Question 3

A Sequencing Batch Reactor (SBR) is a unique form of the activated sludge process. Which phase of the SBR cycle involves adding air to promote the biological breakdown of organic matter and the conversion of ammonia to nitrate?

Accepted Answer

React

Answer

Settle

Answer

Decant

Answer

Fill

Question 4

During the nitrification process, ammonia is converted to nitrate. This biological process has a significant impact on the wastewater chemistry. Which of the following is a key requirement and consequence of nitrification?

Accepted Answer

It consumes a significant amount of alkalinity.

Answer

It generates a large amount of alkalinity.

Answer

It requires anaerobic conditions to proceed.

Answer

It significantly increases the wastewater's pH.

Question 5

An operator of an anaerobic digester is monitoring process stability. Which parameter provides the EARLIEST indication of a potential process upset, often referred to as the digester 'going sour'?

Accepted Answer

An increasing volatile acid to alkalinity ratio.

Answer

A rapid drop in pH.

Answer

An increase in methane gas production.

Answer

A decrease in sludge temperature.

Question 6

A wastewater treatment plant is operating a conventional activated sludge process. If the Food-to-Microorganism (F/M) ratio is consistently too high, what is the most likely operational consequence?

Accepted Answer

Incomplete BOD removal and a turbid, poorly settling effluent.

Answer

The microorganisms will be starved, leading to poor floc formation.

Answer

Sludge bulking due to the growth of old, slow-growing filaments.

Answer

A very stable process with high-quality effluent and low sludge production.