Treatment and Purification of Hard Water

Water treatment

Before water is used in the public water supply, it has to be treated. This treatment does not aim to make the water pure but to make it safe for drinking. The various stages of water treatment include:

1. Filtration - Filtration is the first step, removing large objects such as algae or parasites from the water.

2. Precipitation of mineral salts - Mineral salts, such as iron salts, are precipitated using alum (calcium hydroxide) to remove unwanted compounds from the water.

3. Filtration through a sand bed - This biological process involves filtering water through a sand bed, where a gelatinous layer traps unwanted particles.

4. Chlorination - Chlorination involves treating the water with chlorine to kill harmful bacteria. Chlorine acts as a disinfectant to ensure the water is safe to drink.

5. Fluoridation - Fluoridation is the addition of small amounts of sodium fluoride to water. Fluorides help to harden the enamel on teeth and reduce dental problems. However, not all water supplies are treated in this way.

The importance of safe disposal of used water

While providing clean, safe water is essential for good health, safe disposal of used water is equally important, especially when people live close together in towns and cities. In cities, a system for disposing of used water, known as a sewage system, is crucial.

Sewage treatment process

The processes involved in a sewage treatment plant include the following steps:

1. Removal of large debris - The sewage entering the treatment plant contains debris that may damage pumps and machinery. This debris is removed by screens or vertical bars. After removal, the debris is either burned or buried.

2. Grinding of organic materials - The wastewater then passes through a grinder where organic materials such as leaves are reduced in size to enable efficient treatment and removal later on.

3. Grit removal - In grit chambers, grit (sand and small stones) is removed from the water. The grit is disposed of as sanitary landfill.

4. Sedimentation or flotation - After grit removal, the water enters a sedimentation tank where organic materials settle out. The settled materials are drawn off for disposal. In some cases, flotation is used instead of sedimentation. Air is forced into the wastewater under pressure (1.75 to 3.5 kg/m²), causing suspended solids to rise to the surface. The solids are then removed from the surface.