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What Is Lime Used for in Water Treatment?

Lime (calcium oxide), also known as quicklime, is a chemical compound derived from limestone. According to the National Lime Association, lime is the most used chemical by weight in potable and industrial water treatment.

  1. Water Softening

    • Treating water with hydrated lime (calcium hydroxide) removes hardness caused by carbonate minerals. Treating with lime remedies non-carbonate hardness---that is, hardness resulting from non-carbonate calcium minerals and magnesium salts.

    PH Adjustment

    • Water utilities use hydrated lime to prepare water for treatment processes by adjusting the water's pH. To minimize corrosion of pipes and equipment, utilities add lime to neutralize acidic water.

    Coagulation and Flocculation

    • Water treatment facilities add lime to optimize conditions for coagulation and flocculation, the processes that make suspended particles clump together and settle out of suspension.

    Disinfection

    • Raising water alkalinity to a pH of 10.5 to 11 by adding lime inhibits the growth of bacteria and some viruses.

    Purification

    • Lime removes impurities such as fluoride, iron, manganese and organic tannins from water. The magnesium in dolomitic lime is especially effective in removing silica from water. A side effect of the lime-enhanced softening process is arsenic removal, while disinfection with lime also serves to remove most heavy metals.

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