Exam Study Guide: Bacteria in Anoxic Zones; and Naturally Occurring Ammonia

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 Visual Condition Assessment; and New Service Lines. This time, you can test your knowledge about where bacteria get oxygen in anoxic zones, and treating naturally occuring ammonia.

Wastewater Treatment Sample Question

Where do the bacteria obtain the necessary oxygen to survive in an anoxic zone?

A. Remaining dissolved oxygen
B. Nitrite and nitrate
C. Carbonaceous oxygen
D. The bacteria in an anoxic zone do not require oxygen

Answer: The answer to this question is B. Anoxic zones are generally found in denitrification treatment processes. Anoxic conditions are created when DO has been depleted, leaving oxygen only available in the form of nitrite and/or nitrate. This is normally found post anaerobic zones. This will allow for nitrification, which generates the nitrite and nitrate. The understanding of advanced waste treatment, such as nitrification and denitrification is important for the wastewater operator’s development.

Water Treatment Sample Question

An operator is attempting to disinfect a source water that contains naturally occurring ammonia with a free chlorine residual. For the operator to be successful, what Cl:N ratio must be accomplished?

A. A Cl:N ratio less than 5:1
B. A Cl:N ratio between 5:1 and 6:1
C. A Cl:N ratio between 6:1 and 7:1
D. A Cl:N ratio greater than 7:1

Answer: The correct answer is D. Naturally occurring ammonia concentrations in source waters can vary drastically. Typically, elevated levels of naturally occurring ammonia are associated with water sources supplied from an aquifer. Economically, it becomes more challenging for an operator to surpass breakpoint chlorination and disinfect with a free chlorine residual when naturally occurring ammonia is present at elevated concentrations. Breakpoint chlorination is achieved after all the chlorine and ammonia bonds have decayed and there is nothing else left in the water for the chlorine to react with. This free available chlorine for disinfection is available at Cl:N ratios greater than 7:1

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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