Exam Study Guide - April 2021

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WASTEWATER

By Rick Lallish

In fixed-film processes, what must be reduced before nitrification can occur?

A. Organic loading rate

B. Hydraulic loading rate

C. AOB and NOB bacteria

D. Endogenous respiration

Answer: A. Higher organic loading rates (OLR) favor the growth of heterotrophic bacteria over nitrifying bacteria. In most fixed-film systems, the higher OLRs cause rapid growth of heterotrophic bacteria, forcing the weaker nitrifiers to go deeper into the biomass. This process slows their growth rates. By reducing the OLR, the heterotrophic bacteria will slow, and this prevents the nitrifiers from being overtaken. Operating the system in a series mode where the OLR is reduced after the first stage will allow nitrification in later stages of the process. More information may be found in the WEF Wastewater Treatment Fundamentals 1 – Liquid Treatment textbook, Chapter 9.


DRINKING WATER

By Drew Hoelscher

 How many turns are required to close a 6-inch gate valve?

A. 7.5

B. 14.5

C. 20.5

D. 27

Answer: C. Gate valves are most commonly used to isolate sections of the distribution system during emergency and nonemergency operations. Knowing the exact location and current operating condition of each valve in the distribution system will pay great dividends in an emergency. The size of the valve is also important so an operator will have an idea how many turns will be required to fully open or close it. 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.

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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