Test Yourself Answer

Continued from page 28

1. D) the calcium and magnesium cations measured. Standard Methods for the Examination of Water and Wastewater defines hardness as a result of the calcium and magnesium cations measured.

2. D) All the above.

Source waters with high levels of hardness can shorten the life fabrics, plate and form scale within boilers, and cause scale to form within hot water heaters.

3. A) ion exchange and chemical precipitation. The methods traditionally used to remove hardness are ion exchange and chemical precipitation.

4. D) 30 to 40 mg/l as CaCO3

The minimum hardness level that can be obtained via chemical precipitation, i.e., lime-soda ash softening, is 30 to 40 mg/l as CaCO3

5. C) 0 mg/l as CaCO3

The minimum hardness level that can be obtained via ion exchange is 0 mg/l as CaCO3

6. A) Calcium carbonate

Adding lime to source water with high levels of calcium bicarbonate in order to raise the pH around 10 will result in forming calcium carbonate, thereby removing calcium hardness.

7. B) magnesium carbonate.

Split lime treatment may be utilized to reduce the cost in treating source waters with high levels of magnesium bicarbonate.

8. C) Carbon dioxide

Split lime treatment may reduce the cost of softening due to its ability to reduce the use of carbon dioxide gas, which lowers the pH of the treated water to acceptable levels.

9. A) permanent or noncarbonate hardness. Source waters that cannot be softened to the desired level using lime only have high levels of permanent or noncarbonate hardness and thus must be treated with limesoda ash or lime-caustic soda.

10. D) Iron and manganese

Iron and manganese must be removed from the source water before applying such water to an ion exchange unit as it will reduce the removal efficiency of the unit.