Exam Study Guide: Trickling Filter Components; and Corrosion Control

Maintaining your education is important, especially in a career that demands licensing exams. Prove you’re an expert operator by answering these questions and others from our Exam Study Guide Series.

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Welcome back to TPO magazine's Exam Study Guide Series, which offers a pair of water/wastewater study questions with in-depth explanations of the answers. Last time, we covered a set of wastewater and drinking water treatment questions on the topics of Settled Sludge; and Ladder Safety. This time, you can test your knowledge about trickling filter components, and corrosion control.

Wastewater Treatment Sample Question

What device or part of a trickling filter is responsible for both collecting treated wastewater from the filter media and allowing airflow to the media?

A. Distributor base
B. Outlet box
C. Support grill
D. Underdrain system

Answer: The answer to the question is D. The underdrain system of a trickling filter has dual roles. It serves as the collection point for the flow from the filter and conveys it the underdrain channel as well as permitting the airflow to the media. 

The airflow may be natural or supplemented by a forced air system. It is important for all operators to understand the different modes of wastewater treatment and the equipment we use to perform the operations.

Water Treatment Sample Question

At a surface water treatment plant, what point in the treatment process would NaOH be introduced for corrosion control purposes? 

A. The beginning, to prevent corrosion on treatment plant equipment
B. Towards the end after all other treatment has been accomplished
C. In the distribution system where water has aged
D. At any point where the pH of the water is below 7

Answer: The correct answer is B. In regards to quality, water sources are not equal. The level of treatment and chemical feed point is specific to each source. A surface water source containing particulate matter will most likely require conventional treatment followed by disinfection. 

The coagulation and disinfection processes are typically more successful at lower pH levels. Applying chemicals to raise the pH for corrosion control purposes is more beneficial after all other treatment processes are complete. 

About the authors: Rick Lallish is the Water Pollution Control program director at the Environmental Resources Training Center (ERTC) 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. Lallish was also named the 2017 Illinois Operator of the Year and 2018 president of the Illinois Association of Water Pollution Control Operators.

Drew Hoelscher is the program director of drinking water operations at the Environmental Resources Training Center in Edwardsville, Illinois.


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