Exam Study Guide: Water Chemistry and Water Softening

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 ongoing Exam Study Guide Series.
Exam Study Guide: Water Chemistry and Water Softening

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[Editor’s Note: We’ve enhanced our Exam Study Guide Series to give you more of the content you love. Instead of two short questions per month on the topics of water and wastewater treatment, you’ll now find a pair of study questions every week with high-quality explanations from our expert contributor Ron Trygar of the University of Florida’s TREEO Center. Make no mistake, this will be an excellent resource going forward. Ron is the real deal — check out his bio at the end of this week’s quiz.]

We covered a set of wastewater treatment questions last week involving sewers and hydrogen sulfide, but this time we're focusing on drinking water. Test your knowledge about corrosive components in water chemistry, and the proper use of soda ash in water softening. Take a look at the multiple-choice sample questions and answer explanations below.

Sample Question No. 1:

Which element is considered one of the most corrosive components in water chemistry when found dissolved in water?

A) Ammonia (NH3)

B) Carbon (C)

C) Nitrogen (N2)

D) Oxygen (O2)

Answer: The answer is D, Oxygen (O2). Dissolved oxygen (DO) can be found in water treatment plant source water and finished water entering a distribution system. When water temperature decreases, the ability for that water to be saturated with DO is greater, increasing the potential for corrosion of metal pipe containing ferrous iron. Increased water pressure also allows more DO to be contained in solution. If a water distribution system containing ductile iron, cast iron or steel, a depletion of dissolved oxygen along the long pipe length can be an indicator corrosion is occurring. Other indicators include low water pressure, red water complaints, an increase in leaks and a bitter, metallic taste.

Sample Question No. 2:

The use of soda ash (sodium carbonate) in the lime/soda water softening process is used primarily to remove what?

A) Temporary hardness

B) Carbonate hardness

C) Noncarbonate hardness

D) Bicarbonate alkalinity

The answer is C, noncarbonate hardness. Sodium carbonate (soda ash) is commonly used to remove noncarbonate hardness, also known as permanent hardness. Permanent hardness can be in the form of calcium sulfate or magnesium chloride or sulfate, which are noncarbonate forms of hardness. The amount of noncarbonate hardness can be calculated by subtracting the total hardness from the total alkalinity of a raw water sample. Any hardness in excess of the total alkalinity is considered permanent, or noncarbonate hardness. The addition of soda ash converts calcium sulfate to insoluble calcium carbonate which can be settled out.

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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