Exam Study Guide - August 2020

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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By Rick Lallish

Which of the following pumps would be the least effective for pumping heavy sludges?

A. Progressing cavity

B. Rotary lobe

C. Centrifugal

D. Diaphragm

Answer: C. Progressive cavity pumps are well suited for pumping sludges, especially for dewatering or thickening processes. Of the choices, a centrifugal pump is least suited for this operation. Understanding the different types of pumps and what types of flows they can pump is important for the operator’s knowledge of plant operations. Pumps and pumping questions are included in most states certification examinations. More information can be found in the Water Environment Federation, Operation of Water Resource Recovery Facilities, Manual of Practice No. 11, Chapter 29. 


By Drew Hoelscher

How are slow sand gravity filters backwashed?

A. Slow sand gravity filters are not backwashed.

B. Spraying high-pressure water over the entire surface area until all the sand appears clean.

C. Reversing the flow through the filter at a slow and steady rate until the sand appears clean.

D. Reversing the flow through the filter at a fast and steady rate until the sand appears clean.

Answer: A. Slow sand gravity filters were the first type used in the production of potable water. Through engineering and technology advancements, these filters were replaced with conventional rapid sand filters and high-rate multimedia gravity filters. However, slow sand gravity filters are still sometimes used at water purification plants to filter backwash water before it is discharge to a receiving stream. As with any filter, it eventually becomes exhausted, and an operator needs to clean it by physically removing the top 1-2 inches of sand. After several cleaning cycles, the operator replenishes the sand to the original depth.

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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