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Education/Training + Get AlertsWASTEWATER
By Rick Lallish
Which type of blower may not be operated against a closed valve?
A. Centrifugal
B. Positive displacement
C. High-speed driven (turbo)
D. Open-impeller single-stage
Answer: B. Blowers and pumps have similar characteristics. Positive displacement blowers, like positive displacement pumps, may never be operated against a closed valve. If so, damage will occur to the piping, valves and possibly the blowers. This is an unsafe condition that may cause bodily harm to personnel nearby. Only centrifugal or like blowers may be operated in this manner. More information may be found in the WEF textbook Wastewater Treatment Fundamentals II – Solids Handling and Support Systems, Chapter 8.
DRINKING WATER
By Drew Hoelscher
How are hardness concentrations converted from mg/L as CaCO3 to grains per gallon?
A. Dividing mg/L as CaCO3 concentration by 17.1
B. Multiplying mg/L as CaCO3 concentration by 17.1
C. Dividing mg/L as CaCO3 concentration by 2.5
D. Multiplying mg/L as CaCO3 concentration by 2.5
Answer: A. Typically, systems using ion exchange to soften water discuss hardness in terms of grains per gallon, and systems using precipitation techniques to soften water discuss hardness in mg/L as CaCO3. It may look misleading, but water containing 15 grains of hardness per gallon would be harder than water with 200 mg/L as CaCO3. One grain per gallon is equal to 17.1 milligrams per liter.
About the authors
Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.
