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 new and improved Exam Study Guide Series, which offers a pair of water/wastewater study questions each week with in-depth explanations of the answers. We covered a set of wastewater and drinking water treatment questions last week on the topics of the MLE Process and Monochloramine Production. This week, you can test your knowledge about nitrate conversion and permanganate-greensand filters. Take a look at the multiple-choice sample questions and answer explanations below.
Sample Question No. 1:
During the process of biological nitrogen removal, bacteria known as nitrifiers convert ammonium and ammonia to a final product of nitrate. Which statement below best describes the two-step process?
A) Nitrosomonas convert ammonium to nitrite, then Nitrobacter convert nitrite to nitrate in the aeration tanks.
B) Nitrobacter converts ammonia to ammonium, then Nitrosomonas convert ammonium to nitrate in the aeration tanks.
C) Nitrosomonas convert nitrate to nitrite, then Nitrobacter convert nitrite to nitrogen gas in the anoxic basin.
D) Nitrobacter converts nitrate to nitrogen gas, then Nitrosomonas convert nitrite to nitrate in the anoxic basin.
Answer: The answer is A, Nitrosomonas convert ammonium to nitrite, then Nitrobacter convert nitrite to nitrate in the aeration tanks. Aerobic organisms known as nitrifiers are responsible for the conversion of influent ammonium and ammonia to nitrite then nitrate as a final form of oxidized nitrogen in the process called nitrification. These bacteria can be found in soil and water, and are considered strict aerobes. Nitrifiers perform the conversion of ammonia to nitrate in aerated portions of the activated sludge process, trickling filters and rotating biological contactors (RBCs). Classic training and operation manuals stated the need for elevated levels of dissolved oxygen (DO) to effectively nitrify with DO levels between 1.0 to 3.0 mg/L. Interestingly, in today’s nutrient-removal facilities, operators have shown the ability to simultaneously nitrify and denitrify if DO levels are kept below 1.0 mg/L, in some cases below 0.5 mg/L.
Sample Question No. 2:
The operator of the permanganate-greensand filter water treatment plant is experiencing a light pink colored water leaving the filters. What could cause the pink colored water and what can be used to remove it?
A) An overdose of chlorine is the cause and sulfur dioxide can be used to remove the color.
B) An under-dose of potassium permanganate is the cause and soda ash can be used to remove the color.
C) An overdose of chlorine is the cause and sodium bisulfate will remove the color.
D) An overdose of potassium permanganate is the cause and powdered activated carbon can be used to remove the color.
Answer: The answer is D, an overdose of potassium permanganate is the cause and powdered activated carbon can be used to remove the color. Potassium permanganate is a strong oxidizing agent used to convert soluble iron and manganese to insoluble, particulate form that can be caught on a filter media and removed from the water. When overdosed, potassium permanganate can turn the water a slight pink color, and if dosed too high, can turn the water purple or brown-purple. Powdered activated carbon (PAC) can be used to remove the pink color, but could turn the water a dark color itself. Dark colored water containing PAC must be returned to the plant for retreatment and filtration. Some operators may believe that the problem is due to chlorine overdose since the reagent used for chlorine residual (DPD) also creates a pink color, but this is a false answer.
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.