Exam Study Guide - February 2021


By Rick Lallish

Typically, for an activated sludge process to maintain its operating parameters, what two variables impact the performance process and must be monitored?

A. Temperature and humidity

B. Upstream and downstream processes

C. Federal guidelines and state regulations

D. Time and operating capability

Answer: B. If the upstream and downstream processes run as desired, the activated sludge process can be controlled to meet objectives that include producing floc-forming bacteria, managing the activated sludge (foot/microorganism ratio) and maintaining healthy settleability in the secondary clarifier. Any disruption in the upstream or downstream process can affect the activated sludge process in many ways. An understanding of these processes is key for operators to maintain their facilities and meet NPDES requirements. More information can be found in the Office of Water Programs California State University, Sacramento textbook: Operation of Wastewater Treatment Plants, volume one, eighth edition, Chapter 5.


By Drew Hoelscher

What is most likely to occur if a chlorine cylinder is stored in a room containing temperatures near 160 degrees F?

A. The fusible plugs will melt to prevent any release of chlorine.

B. The fusible plugs will melt, allowing chlorine gas to escape.

C. The chlorine feed rate will drastically decrease due to lack of internal pressure.

D. The chlorine inside the cylinder will only be in liquid form.

Answer: B. Chlorine stored inside steel cylinders expands as temperatures rise, creating excessive internal pressures. The melting of the fusible plug (or plugs) on a chlorine cylinder allows for a more controlled release of excessive pressure from chlorine gas. Fusible plugs melt at around 160 degrees F and are installed on 150-pound cylinders and 1-ton cylinders. The fusible plug on a 150-pound cylinder is located on the valve underneath the valve seat, and a 1-ton cylinder has three fusible plugs on each end.

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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