When operators are faced with licensing exams, they sometimes struggle with test anxiety because they don’t fully understand how to properly study and prepare for exam questions. Here we take a look at a sample wastewater treatment licensing exam question, how to solve the problem, and the correct answer. 

Sample Question:

What is the main difference between primary and secondary clarifiers? 

a) The density of the sludge handled.
b) Number of clarifiers required.
c) Flow rate through clarifiers.
d) Sludge removal systems. 

The primary clarifier is designed to remove floatable solids and scum from the surface and settleable solids from the bottom. Solids collected at the bottom of a primary clarifier are often less dense than in a secondary clarifier simply because of their content. Primary clarifiers remove solids that make up a long list of parameters from debris to fine wastes that come from garbage disposals and infiltration in the collection system. 

Typically, solids in the primary clarifier are inorganic whereas in a secondary clarifier, sludge is nearly 100 percent organic and thus can compact readily, making sludge far denser in a secondary unit than that of a primary system. 

Therefore, the correct answer is a.) The density of the sludge being handled.

About the Author

Mike Smith is program coordinator and lead faculty of the Water Quality Management program at Red Rocks Community College in Lakewood, Colo.

He has been in charge of the multi-faceted training program since 1996.