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

Filamentous bulking is often caused by conditions that favor the growth of filamentous bacteria over floc-forming bacteria. Key causes include low dissolved oxygen (less than 2.0 mg/L), a low Food-to-Microorganism (F/M) ratio, nutrient deficiency, or low pH. These conditions give filamentous organisms a competitive advantage, leading to poor sludge settling and compaction.

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

Denitrification is an anoxic process where facultative bacteria convert nitrate (NO3) to nitrogen gas (N2). This requires three key conditions: the presence of nitrate as an electron acceptor, the absence of free molecular oxygen (anoxic conditions), and a source of readily biodegradable organic carbon (food for the bacteria).

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

The 'React' phase is the primary aeration stage in an SBR cycle. During this phase, oxygen is supplied to the mixed liquor, allowing aerobic bacteria to consume BOD and convert ammonia to nitrate (nitrification). This is the main biological treatment step.

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

The nitrification process consumes approximately 7.14 parts of alkalinity (as CaCO3) for every one part of ammonia-nitrogen oxidized. This consumption of alkalinity can lead to a drop in pH if not buffered adequately. Therefore, maintaining sufficient alkalinity is crucial for a stable nitrification process.

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

The volatile acid to alkalinity ratio is the most sensitive indicator of an impending upset in an anaerobic digester. An increase in this ratio shows that volatile acids are being produced faster than they are being converted to methane, consuming the system's buffering capacity (alkalinity). This change occurs well before a significant drop in pH, providing an early warning for operators to take corrective action.

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Practice Test

Wastewater Operator Biological Treatment Processes Questions and Answers