TABLE OF CONTENTS Michael B.Horsley
Black & Veatch
Kansas City, Missouri
Doug B.Elder, P.E.
Black & Veatch
Olathe, Kansas
Leland L.Harms
Black & Veatch
Kansas City, Missouri
Cold lime softening uses chemical precipitation with lime and other chemicals to reduce a water s hardness and, in some cases, to enhance clarification before filtration. Hot-process softening is predominantly used in industrial applications and is not discussed here. Ion exchange softening is covered in Chapter 12, and membrane processes that may be used to soften water are covered in Chapter 13.
Designing plants with lime softening processes is somewhat different from the design of other types of water treatment plants. Factors responsible for these differences include types of chemicals used, the relatively large quantity of some of these chemicals, the special chemical handling considerations, and the nature of the corresponding chemical reactions. These factors influence process and equipment design and selection, plant layout, and other design considerations.
Hardness in water is the sum of the concentrations of multivalent ions, principally calcium and magnesium. Other ions that produce hardness include iron, manganese, strontium, barium, zinc, and aluminum; but these ions are generally not present in significant quantities. Hardness is generally expressed in terms of equivalent milligrams per liter (mg/L) of calcium carbonate. The sum can also be expressed in milliequivalents per liter. Another expression, used commonly in the past, is grains per gallon, where 17.1 mg/L (as calcium carbonate) is equal to 1 gr/gal.
Total hardness is usually...
