Exam Study Guide - May 2023


By Rick Lallish

Aeration reactors using buoyant free-floating biofilm carriers in an activated sludge process are known as what sort of treatment?

A. Rotating biological contactors

B. Moving bed biological reactors

C. Trickling filters

D. Sequencing batch reactors

Answer: B. Moving bed bioreactors are relatively new treatment options. They consist of aeration basins or activated sludge tanks in some cases retrofitted with small plastic free-floating buoyant media (about 25-67% of the tank volume). This is a hybrid of activated sludge and fixed-film treatment. The most common use is in plants looking for increased nitrification and total nitrogen removal. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals III: Advanced Treatment, Chapter 4.


By Drew Hoelscher

What soil type is most likely to cause a cave-in during excavation work?

A. Stable Rock

B. Type A

C. Type B

D. Type C

Answer: D. Type C soil is less cohesive than Type A or Type B; it is more granular material that does not stick together. However, Type A soil is automatically classified as Type C when water is present because it is no longer as stable. Precautions and protective systems should always be provided when the depth of a trench is greater than 5 feet or a competent person has identified a potential hazard. OSHA 29 CFR Part 1926, Subpart P, can provide additional excavation safety standards and practices.

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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