What Do You Know About Hardness Removal?

Charlie Lee Martin Jr., Ph.D.

1. Standard Methods for the Examination of Water And Wastewater defines hardness as a result of a. the aluminum and lead cations measured. b. the arsenic and mercury cations measured. c. the manganese and sodium cations measured. d. the calcium and magnesium cations measured.

2. Source waters with high levels of hardness can a. shorten the life of fabrics. b. plate out and form scale within boilers. c. cause scale to form within hot water heaters. d. All of the above.

3. The method(s) traditionally used to reduce or remove hardness is (are) a. ion exchange and chemical precipitation. b. reverse osmosis. c. slow sand filtration. d. greensand filtration. a. 100 to 150 mg/l as calcium carbonate (CaCO3) b. 0 to 30 mg/l as CaCO3 c. 80 to 90 mg/l as CaCO3 d. 30 to 40 mg/l as CaCO3 a. 15 mg/l as CaCO3 b. 30 mg/l as CaCO3 c. 0 mg/l as CaCO3 d. 50 mg/l as CaCO3 a. Calcium carbonate b. Lead carbonate c. Aluminum carbonate d. None of the above.

4. What is the minimum hardness level that can be obtained via chemical precipitation, i.e., lime-soda ash softening?

5. What is the minimum hardness level that can be obtained via ion exchange?

6. Adding lime to source water with high levels of calcium bicarbonate in order to raise the pH around 10 will result in forming which compound?

7. Split lime treatment may be utilized to reduce the cost in treating source waters with high levels of a. manganese bicarbonate. b. magnesium bicarbonate. c. calcium bicarbonate. d. iron bicarbonate. a. Nitrogen b. Oxygen c. Carbon dioxide d. None of the above.

8. Split lime treatment may reduce the cost of softening due to its ability to reduce the use of which gas?

9. Source waters that cannot be softened to the desired level using lime only have high levels of a. permanent or noncarbonate hardness. b. temporary or carbonate hardness. c. permanent or carbonate hardness. d. temporary or noncarbonate hardness. a. Manganese and lead b. Iron and lead c. Lead and copper d. Iron and manganese

10. Which two constituents of source water must be removed before applying such water to an ion exchange unit?

Answers on page 50

References used for this quiz:

• Water Treatment Plant Operation, Volume 2, Seventh Edition, CSU

Sacramento, Chapter 2 - Softening

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Readers are welcome to submit questions or exercises on water or wastewater treatment plant operations for publication in Test Yourself. Send your question (with the answer) or your exercise (with the solution) by email to: charmartin@msn.com