Exam Study Guide - July 2020

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By Rick Lallish

What is the correct way to express the organic loading rate on a trickling filter?

A. Pounds of BOD per square foot of media per day

B. Pounds of BOD per cubic foot of media per day

C. Pounds of BOD per 1,000 square feet of media per day

D. Pounds of BOD per 1,000 cubic feet of media per day

Answer: D. The organic loading on a trickling filter is an important factor for proper operation. Simply, it is the amount of organic matter (BOD) fed to the trickling filter per day. We express this as pounds of BOD per thousand cubic feet of media per day (pounds of BOD/1,000 ft³/day). When calculating the organic loading rate, take into account all the surface area of the media from the surface to the bottom (i.e., the volume of media). Do not take into account the recirculation flow, as the formula only accounts for the flow and BOD concentration. More information may be found in the Office of Water Programs California State University, Sacramento textbook: Operation of Wastewater Treatment Plants, volume one, eighth edition, Chapter 6.


By Drew Hoelscher

What is the best approach when collecting a routine total coliform sample?

A. Flushing the hot-water tap for about five minutes before collecting

B. Flushing the cold-water tap for about five minutes and rinsing the bacteriological sample bottle before collecting

C. Flushing the cold-water tap for about five minutes before collecting

D. Collecting a first-draw sample from the cold-water tap

Answer: C. One way to monitor the quality of potable water flowing through the distribution system is to collect routine coliform samples every month. Thoroughly flushing the cold-water service line before collecting a bacteriological sample ensures that the water collected is from the distribution main. In addition, the operator should always measure and record the chlorine residual before collecting the bacteriological sample.

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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