Exam Study Guide


By Rick Lallish

What process control measure has the most influence on sludge quality and determines the sludge age in an activated sludge process?

A. RAS (return activated sludge)

B. WAS (waste activated sludge)

C. SVI (sludge volume index)

D. F/M (food to mass ratio)

Answer: B. In an activated sludge facility, the operator must understand each process control measure. This includes understanding how measures such as RAS and WAS affect sludge quality. Operators must also know when to adjust and use these parameters to operate the plant to meet effluent standards. WAS is the measure that determines how long the mixed liquor suspended solids, or MLSS, remain in the system (solids retention time). WAS also determines the MLSS concentration. High wasting rates leave fewer solids in the system.


By Drew Hoelscher

What form of iron passes through a sand filter and typically causes dirty-water complaints from customers?

A. Ferrous bicarbonate

B. Ferric hydroxide

C. Insoluble iron

D. Fe(OH)3

Answer: A. Public water supplies that use groundwater as their source typically have to combat high iron levels in the raw water. Raw groundwater with high concentrations of soluble ferrous bicarbonate will appear clear until the soluble iron is oxidized by dissolved oxygen or a chemical oxidant. To reduce discolored-water complaints, iron should be completely oxidized and removed at the treatment plant. Ferrous bicarbonate that passes through the plant and distribution system may become oxidized inside customers’ homes and stain laundry and fixtures.

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.  


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