Wastewater Operator Preliminary and Primary Treatment Questions and Answers

Question 1

What is the primary purpose of a grit chamber in the preliminary treatment phase of a wastewater treatment plant?

Accepted Answer

To remove heavy, abrasive inorganic particles like sand and gravel.

Answer

To remove large solid objects like rags, plastics, and sticks.

Answer

To allow for the settling of organic solids and reduce BOD.

Answer

To shred and grind large solids into smaller, more uniform pieces.

Question 2

A properly functioning primary clarifier can be expected to remove approximately what percentage of Biochemical Oxygen Demand (BOD)?

Accepted Answer

25-40%

Answer

5-15%

Answer

50-70%

Answer

80-95%

Question 3

An operator at a treatment plant notices that the primary clarifier's effluent has a high concentration of suspended solids and the sludge blanket is rising. Which of the following is the MOST likely cause?

Accepted Answer

The sludge withdrawal rate is too low.

Answer

The influent flow rate is too low, causing solids to decompose.

Answer

The comminutor located upstream is malfunctioning.

Answer

The grit chamber is removing too much organic material.

Question 4

Which of the following pieces of equipment is designed to cut and shred large solids in the wastewater stream without removing them from the flow?

Accepted Answer

Comminutor

Answer

Bar Screen

Answer

Grit Classifier

Answer

Primary Clarifier Skimmer

Question 5

The main objective of preliminary wastewater treatment processes is to:

Accepted Answer

Protect downstream equipment and subsequent treatment processes.

Answer

Disinfect the wastewater to kill pathogens.

Answer

Remove dissolved organic matter through biological action.

Answer

Stabilize sludge before final disposal.

Question 6

In a primary clarifier, the physical process responsible for the removal of settleable solids is:

Accepted Answer

Gravity

Answer

Filtration

Answer

Chemical precipitation

Answer

Biological uptake