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 Sludge Blanket Depth; and Aluminum Sulfate as a Coagulant. This time, you can test your knowledge about different types of wastewater treatment bacteria and the proper sequence to add chemicals in water treatment.
Wastewater Treatment Sample Question:
Of the types of bacteria found in the activated sludge process, what group of bacteria gets its energy and carbon from organic compounds that are produced by other microorganisms and not itself?
A. Necrotrophic
B. Autotrophic
C. Heterotrophic
D. Anaerotrophic
Answer: The answer to the question is C. In wastewater treatment, the two forms of bacteria the operator is most concerned with are heterotrophic and autotrophic bacterium. Being able to identify what form of bacteria is present allows an operator to make decisions on the proper operation of his/her plant. It is also helpful to know what bacteria can survive in certain types of zones. Heterotrophic bacteria grow faster in energy-rich organic zones, whereas autotrophs will flourish in energy-poor zones (ammonia or nitrifying zones).
According to the Water Environment Federation OM-9, “There are two main types of bacteria in the activated sludge process. The first group is the Heterotrophs. Hetero means other and troph means feeder. Heterotroph literally translates to an organism that feeds on others. The bacteria do not literally consume one another, but they do get their energy and carbon from organic compounds that were produced by other microorganisms and not themselves.”
Water Treatment Sample Question
What would be the result of feeding chlorine for disinfection prior to feeding activated carbon for taste and odor control?
A. Increase in chlorine residual
B. Decrease in chlorine residual
C. Decrease in chlorine costs
D. Increase in log removal credit
Answer: The correct answer is B. Activated carbon and chlorine are both common and effective chemicals when applied in the proper sequence. Activated carbon helps control taste and odor issues by adsorbing organics and removing them through sedimentation and filtration. Activated carbon also acts as a reducing agent when chlorine is present. The exchange of electrons causes chlorine to reduce to the chloride ion.
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.
