WASTEWATER

By Rick Lallish

By allowing a settleometer sample to set for several hours after the 30-minute settling test, what can be determined?

A. Denitrification in the system

B. Filamentous identification

C. Septicity and toxicity of sample

D. MLSS concentration

Answer: A. If you allow a sample to sit for several hours after the 30-minute settling analysis, the sample will eventually rise or flip over and float to the top of the settleometer. This is an indication of denitrification. It is a common occurrence and is expected. The amount of time it takes gives operators an idea of possible problems in the clarifier. If the sludge rises too fast (90 minutes or less), you should check the sludge blanket and make possible adjustments (increase) to the return activated sludge levels. More information may be found in the WEF textbook Wastewater Treatment Fundamentals I: Liquid Treatment, Chapter 8.

DRINKING WATER

By Drew Hoelscher

What temperature should be maintained in a room storing liquid chlorine containers?

A. Less than 50 degrees F so the cylinders or containers do not build up pressure.

B. At least 65 degrees F, but not to exceed 100 degrees F.

C. Greater than 100 degrees F or the liquid will not convert to a gas.

D. Temperature is not important because the containers are sealed carbon steel vessels.

Answer: B. Buildings storing chlorine containers should be isolated from the rest of the treatment plant and be equipped with a climate control system. Ideally, the temperature should be kept around 70 degrees F. If the temperature is too low, the chlorine gas being withdrawn can condense and return to its liquid form. If the temperature is too great, the container will become over pressurized and may cause a fusible plug to melt.

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.