WASTEWATER
By Rick Lallish
How is wasting accomplished when operating a sequencing batch reactor?
A. Immediately after the react stage
B. During the react stage (about halfway through the stage)
C. During the decant stage
D. During the idle stage
Answer: D. Typical sequencing batch reactors are single-tank wastewater treatment systems that operate in a five-stage process (fill-react-settle-decant-idle). When operating properly, the wasting is done during the idle stage before starting a new sequence. During this stage a small amount of the MLSS or activated sludge is pumped out as necessary. Most SBRs are computer-operated, using sensors and timers. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals III: Advanced Treatment, Chapter 4.
DRINKING WATER
By Drew Hoelscher
What is the maximum chlorine gas withdraw rate from a 150-pound cylinder?
A. 150 pounds per day
B. 75 pounds per day
C. 40 pounds per day
D. 25 pounds per day
Answer: C. Maximum chlorine gas withdraw rates vary based on temperature. It is not recommended to feed more than 40 pounds of chlorine gas per day from a single 150-pound cylinder. Excessive gas withdraw rates may cause issues due to the gas being withdrawn faster than the liquid is being converted to a gas.
About the author(s)
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.
