WASTEWATER
By Rick Lallish
What is the most common type of lagoon currently in use to treat municipal wastewater?
A. Anaerobic
B. Aerated
C. Polishing
D. Facultative
Answer: D. The most common lagoon treatment system in use today is the facultative lagoon. These lagoons are typically 3 to 8 feet deep. They have dual layers: an aerobic layer on top and an anaerobic layer below. The algae in the aerobic layer supply the dissolved oxygen. Light penetration determines the aerobic layer’s depth. The waste byproducts from the aerobic layer trickle down to the anaerobic layer, where digestion takes place. The two layers supplement each other. Controlled discharges of these lagoons may provide detention times of up to 180 days. The ability to identify different types of lagoons is key for the operator certification studies. 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 8.
DRINKING WATER
By Drew Hoelscher
To develop a disinfection profile for the reduction of Giardia lamblia, an operator needs to know:
A. The dimensions of the basins in each disinfection segment, baffling factor, water pH, peak hourly flow rate, water temperature and chlorine residual
B. The dimensions of the basins in each disinfection segment, peak hourly flow rate, water temperature and chlorine residual
C. The dimensions of the basins in each disinfection segment, water pH, water temperature and chlorine residual
D. The dimensions of the basins in each disinfection segment, baffling factor, peak hourly flow rate and chlorine residual
Answer: A. Disinfection profiles are developed to ensure that log inactivation requirements are achieved. To calculate log inactivation credits, the operator needs to know the disinfectant residual concentration and the time for which the concentration is in contact with the water. Once this is established, the operator uses the log reduction tables created by U.S. EPA to determine the inactivation credit for Giardia lamblia. A technical guidance manual is accessible by visiting:
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=20002649.txt
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.
