Exam Study Guide - March 2020

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WASTEWATER By Rick Lallish

In pump hydraulics, what condition is a measurement of the physical vertical distance between the surfaces of two fluids, but is not related to how far the fluids are apart horizontally?

A. Specific gravity

B. Lift

C. Static head

D. Dynamic head

Answer: C. Static head is the physical vertical distance between the surfaces of two fluids no matter the physical distance apart horizontally. Dynamic head is the theoretical distance rather than the physical distance. Both conditions are measured in feet of head. More information may be found in the textbook Pumps and Pumping by Skeet Arasmith, 2011.


DRINKING WATER By Drew Hoelscher

An operator is attempting to disinfect a source water that contains naturally occurring ammonia with a free chlorine residual. For the operator to be successful, what Cl:N ratio must be accomplished?

A. Any Cl:N ratio less than 5:1

B. Any Cl:N ratio between 5:1 and 6:1

C. Any Cl:N ratio between 6:1 and 7:1

D. Cl:N ratio greater than 7:1

Answer: D. Naturally occurring ammonia concentrations in source waters can vary drastically. Typically, elevated levels of naturally occurring ammonia are associated with water sources supplied from an aquifer. Economically, it becomes more challenging for an operator to surpass breakpoint chlorination and disinfect with a free chlorine residual when natural ammonia is present at elevated concentrations. Breakpoint chlorination is achieved after all the chlorine and ammonia bonds have decayed and there is nothing else left in the water for the chlorine to react with. This free available chlorine for disinfection is available at Cl:N ratios greater than 7:1.


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.



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