Exam Study Guide - April 2020

Interested in Education/Training?

Get Education/Training articles, news and videos right in your inbox! Sign up now.

Education/Training + Get Alerts

WASTEWATER By Rick Lallish

While operating an automatic composite sampling device, you notice elevated TSS or BOD in the effluent sample. What could be causing this problem?

A. Not enough samples in the 24-hour period

B. Refrigerator temperature set too low

C. Dirty labware/operator error

D. Sample tubing residue

Answer: D. Automatic samplers are outstanding and generally reliable devices if maintained properly. Dirty tubing can lead to elevated TSS or BOD readings in the effluent samples. The residue is biological growth and, if left unchecked, it will cause many problems. Periodic cleaning or changing of the rubber or plastic tubing is necessary. Other problems to look for include low battery causing the sample to warm and begin bacterial growth, clogged strainers and dirty sample bottles. More information can be found in the California State University, Sacramento textbook, Operation of Wastewater Treatment Plants, volume one, eighth edition, Chapter 9. 

DRINKING WATER By Drew Hoelscher

An operator has a 100-gallon chemical day tank containing 60 gallons of water. How many pounds of chemical should the operator add to the tank to prepare a 10% solution by weight?

A. 6

B. 10

C. 35.5

D. 55.6

Answer: D. When asked to make a solution with a percent-by-weight concentration, the weight of the water plus the weight of the chemical are taken into account. For instance, 60 gallons of water weighs 500.4 pounds and should only contribute to 90% of the total weight if the desired concentration is 10% chemical.

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.


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.