Exam Study Guide: Trickling Filters

Exam Study Guide: Trickling Filters

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When faced with a licensing exam, don't struggle with test anxiety! Use the question below and others from our Exam Study Guide series to properly study and prepare for exam questions. Take a look at this sample wastewater treatment licensing question along with an explanation of the correct answer.

Sample question:

Besides collecting treated water from under the filter media, what is the purpose of the underdrain system of a rotary arm trickling filter?

A) Allow the calibration of the rotary arm flow distribution

B) Permits airflow through the media

C) Regulates flow of filter effluent

D) Provides higher water head to maintain equal flow


Underdrains are typically 1 to 2 feet deep to allow for the removal of effluent, and they serve as an air conduit to the interior of the trickling filter. Thus it serves a dual purpose. The answer is therefore, B.

Source: WEF MOP11 21-15

About the author
Ricky Lallish is the Water Pollution Control, program director at the Environmental Resources Training Center of Southern Illinois University Edwardsville. He provides training for entry level operators in the wastewater field and operators throughout the state looking to further their education.


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