Why Lime is Used in Water Treatment Plants

Water treatment plants are designed to provide potable water for consumption, industrial use, and other purposes. However, raw water sources may contain various contaminants, such as suspended solids, dissolved minerals, organic matter, and microorganisms. These contaminants need to be removed or reduced to safe levels before the water can be distributed to consumers. One of the common methods used in water treatment plants is lime treatment.

What is Lime Treatment?

Lime treatment is a process that involves adding lime (calcium oxide or calcium hydroxide) to water to raise the pH level and precipitate dissolved impurities. When lime is added, it reacts with carbon dioxide in water to form calcium carbonate, which settles down as floc with impurities, such as metals, silica, and organic matter. Lime treatment also disinfects the water by killing bacteria and viruses that are sensitive to high pH values.

Advantages of Lime Treatment

The use of lime in water treatment offers several advantages, such as:

Effective removal of hardness-causing minerals, such as calcium and magnesium ions, that can cause scaling and corrosion in pipes and appliances, and affect the taste and appearance of water.

Reduction of heavy metals, such as iron, manganese, and lead, that can be toxic and cause staining, odor, and taste problems.

Enhancement of coagulation and sedimentation processes that remove suspended solids and turbidity from water.

Disinfection of water by increasing the pH level to 11-12, which kills most bacteria, viruses, and parasites.

Control of odor and taste problems caused by algae, bacteria, and organic matter.

Limitations of Lime Treatment

Despite its advantages, lime treatment has some limitations that need to be considered, such as:

High cost and complexity of lime storage, handling, and dosage compared to other treatment chemicals.

Possible interference with the water chemistry and quality by adding excessive amounts of lime.

Potential health and environmental risks associated with lime dust and sludge, which may contain hazardous substances like arsenic, cadmium, and chromium.

Limited effectiveness against some contaminants, such as viruses and protozoa, that are resistant to high pH values.

Need for careful monitoring and control of lime dosage and pH level to avoid over-treatment or under-treatment.

Conclusion

Lime treatment is a common method used in water treatment plants to improve the quality and safety of drinking water. Although lime treatment has some drawbacks, its benefits outweigh its limitations in most cases. The use of lime in combination with other treatment processes, such as filtration and chlorination, can provide a more comprehensive and reliable means of water purification.