Here are the answers to the Jan. 19, 2021 edition of TPO's Exam Study Guide:

1. For primary clarifiers, what is the design parameter for hydraulic detention time?
The answer to the question is B, 1.5 to 2.5 hours. The design parameters for primary clarifiers is generally designed for a hydraulic detention time of 1.5 to 2.5 hours, sludge blanket depth of 2 to 3 feet, and sludge concentrations of 3% to 6% total solids. These standards are from the WEF MOP 8, Design of Water Resource Recovery Facilities. Understanding design parameters of the wastewater plant equipment and processes is very important for operator knowledge. Having an idea of what to expect from these processes makes the operator’s job much easier. Note, these are generally accepted design parameters and may be flexible in some instances. The design in some plants may be slightly different.

2. How many turns are required to close a 6-inch gate valve?
The correct answer is C, 20.5. Gate valves are most commonly used to isolate sections of the distribution system during emergency and nonemergency operating situations. Knowing the exact location and current operating condition of each valve in the distribution system will pay great dividends in an emergency situation. In addition, the size of valve is also important so an operator will have an idea of how many turns will be required to fully open or close the valve. The gate valve open/close operating formula is three times the valve size plus two or three turns. Example: 6 X 3 = 18 + 2 or 3 = 20-21 turns.