Exam Study Guide - July 2019

WASTEWATER - By Rick Lallish

What type of pond is often used to treat strong industrial wastes?

A. Aerobic

B. Anaerobic

C. Facultative

D. Mechanically aerated

Answer: B. Anaerobic ponds are most often used to treat strong industrial and agricultural wastes. Some are used for pretreatment as well. They are used to reduce wastewater strength and do not provide complete treatment. They are normally followed by a more conventional treatment method. Anaerobic ponds are devoid of any oxygen sources, including nitrate or nitrite. More information can be found in the Water Environment Federation training manual, Wastewater Treatment Fundamentals 1 – Liquid Treatment, Chapter 6.

DRINKING WATER - By Drew Hoelscher

What is the brake horsepower (BHp) of a 75% efficient pump that is pumping water 300 gpm against 150 feet of total dynamic head (TDH)?

A. 5 BHp

B. 10 BHp

C. 15 BHp

D. 20 BHp

Answer: C. Water weighs 8.34 pounds per gallon, so moving it requires a lot of energy and work. Work is expressed in foot-pounds. One hp is equal to 33,000 ft-lbs per minute, so multiplying the weight of the water (300 gpm x 8.34 pounds = 2,502 pounds) by the distance (150 TDH) and dividing by 33,000 ft-lbs per minute will calculate the water horsepower (WHp). The WHp is the horsepower transferred to the water from the pump. To determine the BHp, divide the WHp by the percent efficiency of the pump (0.75). The BHp is the output horsepower from the motor to the shaft. Motors are not 100% efficient, and you can determine the required electrical horsepower (EHp) by dividing the BHp by the percent efficiency of the motor.


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