WASTEWATER By Rick Lallish

What is the condition on a rotating biological contactor (RBC) that is identified by uneven shaft rotation, usually caused by uneven biofilm growth causing unbalanced weight distribution?

A. Chaining

B. Loping

C. Fouling

D. Tepidity

Answer: B. Although RBCs are not as commonly used as in the past, knowledge of the operation and troubleshooting conditions is still important to a well-rounded operator. Loping is a common problem on RBCs. It is caused by uneven biofilm growth. The unbalanced weight condition causes the rotational speed to vary cyclically with each rotation. This causes the wheels to seem to jump or jerk. Gears may be damaged if this is not corrected. More information can be found in the Water Environment Federation textbook: Wastewater Treatment Fundamentals I – Liquid Treatment, Chapter 7.

DRINKING WATER By Drew Hoelscher

How can an operator determine the approximate amount of noncarbonate hardness in a water sample?

A. Take the average of the total hardness and the total alkalinity

B. Subtracting the total alkalinity from the total hardness

C. Add the total alkalinity and the total hardness

D. Divide the total hardness by two

Answer: B. After analyzing a water sample for total hardness and total alkalinity, an operator can determine the approximate amount of noncarbonate hardness by subtracting the total alkalinity from the total hardness. The difference between the two indicates the approximate amount of calcium and magnesium ions linked to other ions, such as sulfate and chloride (noncarbonated hardness). When the total hardness is less than or equal to total alkalinity, calcium and magnesium ions are linked to carbonate and bicarbonate ions (carbonate hardness), and the amount of carbonate hardness is equal to total hardness, indicating that noncarbonate hardness is not present.

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