Exam Study Guide: Activated Sludge Bacteria; and Properties of Chlorine

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.

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 Influent Wastewater Alkalinity; and Ion-Exchange Softening Plant Operation. This time, you can test your knowledge about activated sludge bacteria, and the properties of chlorine.

Wastewater Treatment Sample Question:

The bacteria found in the activated sludge process convert waste that is normally nonsettleable into what product?

A. Biofilm that will grow on rock or plastic media

B. Biomass flocs that are heavy enough to settle

C. Dense anaerobic sludge mass that will float

D. Magnesium-ammonium-phosphate crystals

Answer: The answer is B, biomass flocs that are heavy enough to settle. The activated sludge process is widely used to provide bacteria that are suspended in a liquid matrix the time and available oxygen to convert dissolved organic matter and colloidal solids and into by-products of water, carbon dioxide and energy for bacteria to reproduce.  The resulting growth of the biomass produces bacteria colonies (floc) that increase in size and density. As the flocs grow and age, they become heavier than the water surrounding them and will settle to the bottom of a basin given the opportunity. Settling can occur in a separate basin called a clarifier, or in the case of a sequencing batch reactor (SBR), during the settle phase of treatment.

In case you were wondering about answer choice D, magnesium-ammonium-phosphate crystals are also known as struvite, a kind of mineral scale that forms inside pipes and on equipment usually associated with anaerobic digestion.

Water Treatment Sample Question:

Which of the choices below contains the correct statements about the properties of chlorine?

A. Chlorine gas is lighter than air, highly flammable and odorless

B. Chlorine has atomic number 17, is a halogen and a powerful oxidizer

C. Chlorine is heavier than air with a distinct rotten egg odor and common in manholes

D. Chlorine is odorless and is used to lower the pH of water

Answer: The answer is B, chlorine has an atomic number 17, is a halogen and a powerful oxidizer. Chlorine is used in so many processes in both drinking water and wastewater treatment since the early 1800s. It is a powerful oxidizer, gaining an electron from other elements in its attempt to become complete in its outer electron shell.

Answer choice A is a description of methane, C describes hydrogen sulfide and D describes carbon dioxide.

About the author: Ron Trygar is the senior training specialist for water and wastewater programs at the University of Florida's TREEO Center. Previously, he was the wastewater process control specialist at Hillsborough County Public Utilities in Tampa, Florida. He has worked in the wastewater industry for more than 30 years in a variety of locations and positions. Trygar became a Certified Environmental Trainer (CET) in 1998 and has since provided training for associations and regulatory agencies such as Florida Department of Environmental Protection (FDEP); Florida Water and Pollution Control Operators Association Short Schools; USABlueBook; Florida Water Environment Association sponsored training events; and local school environmental programs. Working alongside the FDEP Northeast District, Trygar helped begin the Florida Rural Water Association and FDEP joint operator certification review classes that are still given around the state today. He holds a Florida Class A wastewater treatment operator’s license and a Florida Class B drinking water operator’s license.


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