WASTEWATER By Rick Lallish

What is the maximum blanket level in a secondary (activated sludge) clarifier?

A. 5%

B. 10%

C. 25%

D. 50%

Answer: C. Basic operation and knowledge of clarifier process controls are fundamentals that most operators should understand. In activated sludge processes, the sludge blanket should never exceed 25% of the sidewall depth of the secondary clarifier. In some texts, a 2-foot blanket is recommended. Whenever the blanket approaches or exceeds this depth, operators should take precautions. This is usually an indicator of problems such as filamentous bulking or equipment malfunction. The blanket should be checked daily, preferably at about the same time each day. More information can be found in the Water Environment Federation training manual, Wastewater Treatment Fundamentals 1 – Liquid Treatment, Chapter 8.

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DRINKING WATER By Drew Hoelscher

What is the best backflow control device for protecting a potable waterline from contamination?

A. Reduced-pressure zone

B. Air gap

C. Double check

D. Vacuum breaker

Answer: B. An air gap provides complete separation between potable water and a potential source of contamination. This complete separation must be at least two times the internal diameter of the potable water supply line, but no less than 1 inch. However, it is not always possible to have a complete separation, so a reduced-pressure-zone assembly would be installed on the potable supply line if the potential contamination poses a health hazard to the public.

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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.