WASTEWATER
By Rick Lallish
Duckweed can be a nuisance and cause problems in facultative lagoons. What is the recommended method of controlling duckweed outbreaks?
A. Apply large amounts of HY-var to the influent flow
B.Add live Daphnia to the lagoon
C. Physical removal
D. Allow the duckweed to flourish, as it will assist the algae with dissolved oxygen
Answer: C. Some treatment facilities actually use duckweed to control excessive algae growth. However, duckweed is an extremely aggressive plant and can overtake a facultative lagoon cell in a very short time. The most recommended method of controlling duckweed is to physically remove it. This can be done by using a boat with a rake or board in the front, pushing the duckweed to the bank and removing it. Herbicide may be used in some cases but only with regulatory authority and proper application certification (in some states). Chemical treatment of lagoons should be a last option. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals I: Liquid Treatment, Chapter 6.
DRINKING WATER
By Drew Hoelscher
Which assembly will protect a water main from a fire-suppression system and identify illegal water usage from the fire-suppression waterline?
A. DCV
B. RPZ
C. AVB
D. RPDA
Answer: D. A cross-connection-control program is one method public water supplies use to help protect the distribution system from contamination. Public water supplies are responsible for the quality of the water delivered to the end user, so it is important to identify high-risk connections and protect the distribution system with backflow preventers. Operators typically use the survey method, and site visits when necessary, to gather initial service connection information. The reduced pressure detector assembly is equipped with a meter on the bypass line to detect leaks or unauthorized water usage.
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.
