WASTEWATER By Rick Lallish

What condition occurs when the sludge age advances and there is less food available per bacteria?

A. Flocculation

B. Nocardia filaments

C. Excessive white foam

D. Endogenous respiration

Answer: D. A portion of the bacteria can be lost due to endogenous respiration at high sludge ages. This is due to the lack of food available or an unbalanced food-to-microorganism (F/M) ratio. The bacteria will consume their own cell mass and exopolymer to survive. This will provide food for the other bacteria as well. Understanding the natural cycle of life and conditions in an activated sludge treatment process gives operators useful knowledge for troubleshooting. More information may be found in the Water Environment Federation textbook: Wastewater Treatment Fundamentals I – Liquid Treatment, Chapter 8.

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DRINKING WATER By Drew Hoelscher

A well with an encrusted screen can cause which of these to occur?

A. Decrease in the specific capacity in gpm/ft of drawdown

B. Increase in the specific capacity in gpm/ft of drawdown

C. Decrease in drawdown

D. Increase in the static level 

Answer:  A. Over time, well screens become plugged due to dissolved minerals in the water coming out of solution and collecting on the screen openings. Calcium and magnesium carbonate will precipitate out of the water rather easily under high-velocity and low-pressure conditions. This is one reason well drillers and engineers design a well to limit the velocity of the water entering the well to 0.1 feet per second or less. As the screen plugs, water is restricted from entering the well, which increases the drawdown and ultimately decreases the gpm/ft of drawdown (specific capacity).

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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.