Exam Study Guide: Bacterial Functions; and Water Filtration Processes

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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 Advantages of Plastic Media; and Treating Colder Water. This time, you can test your knowledge about Nitrosomonas and Nitrobacter function, and the water filtration processes.

Wastewater Treatment Sample Question:

Nitrosomonas and Nitrobacter bacteria perform what function of the activated sludge process?

A) They are responsible for denitrification

B) They are required for restoring alkalinity to the process

C) They convert the nitrate into nitrous oxide and nitrogen gas

D) They convert ammonium into nitrite and nitrate

Answer: Nitrosomonas and Nitrobacter bacteria are responsible for nitrification, the oxidation process where ammonium is first converted to nitrite then the nitrite is further oxidized to nitrate. So the answer is D, they convert ammonium into nitrite and nitrate. Nitrification occurs mostly within an aerated basin like an aeration tank, but can occur in other aerated locations like wetlands, rivers and streams, and within soils. We refer to these organisms as aerobic autotrophs.

Answer choices A, B and C are all referrals to denitrification where facultative heterotrophic bacteria reduce the nitrate to a final product of nitrogen gas. There are other bacteria that convert ammonium to nitrate including Nitrosococcus and Nitrosospira, however Nitrosomonas and Nitrobacter have remained the most well known and most commonly referenced nitrifying organisms.

Water Treatment Sample Question:

What filtration process requires filter media to be added to the water being treated as slurry where it collects on a septum or other appropriate screening device?

A) Slow sand filtration

B) Multimedia filtration

C) Diatomaceous earth (DE) filtration

D) Gravity filtration

Answer: The answer is C, diatomaceous earth (DE) filtration. You may have come across DE filters in the food and beverage industry or at a swimming pool. They're used where very high clarity water is required, but a unit with a small footprint is needed. Diatomaceous earth is a type of naturally occurring soft rock that easily disintegrates into a fine white powdery substance, and is found in the earth’s crust around the world. DE powder is mostly the remains of fossilized diatoms made of silica, but could also contain iron and alumina.

In water filtration plants using DE powder, the powder is added to the filter inlet water as a pre-coat that accumulates on a mesh media device. The water is filtered as it passes through the media coated with the DE powder. Additional DE powder is added to the water occasionally to keep the filter operating optimally.

DE filtration is not commonly found in water filtration plants, but is finding a place in the flow scheme of desalination plants using reverse osmosis. DE filtration prior to the RO membranes creates a very clear water with a low silt density index, increasing the efficiency of the membrane treatment process.


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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