Hard water is the water that contains more than 60 mg/l Calcium, Magnesium and other metal ions. When water source contains limestone or chalk rock which largely made-up of calcium and magnesium carbonate, then that water may contain hardness and we need to remove the hardness by using water softener or base exchanger.
Problems due to hard water:
Scale-producing hard water is responsible for the loss of hundreds of thousands of litters of water, because hard water is an ineffectual cleaner, requiring more soap and longer rinse cycles to achieve the same result as softer water. Hard water gets feed into boiler, this will block the water tube due to deposition of scale inside the boiler piping. Also some common problem due to hard water are as follows;
- Blocking of piping system
- Loss of water pressure due to reduced pipe diameter
- Bacterial growth in drinking water carrying pipes
- Loss of energy in the hot water circuit and high costs for heating
- High cleaning costs and the need of aggressive cleaning agents
- Hard water causes malfunctioning machinery
- High production costs due to maintenance
- Long pauses in production when machinery has to be maintained and cleaned leading to inefficient production planning
- Decrease in productivity due to hard water
The most common means for removing water hardness rely on ion-exchange or reverse osmosis. Other approaches include precipitation methods and sequestration by the addition of chelating agents.
Types of Hardness:
Water hardness is classified as Temporary hardness and Permanent hardness.
Temporary Harness is a type of water hardness caused by the presence of dissolved bicarbonate. When these minerals are dissolved in water it dissociates in calcium and magnesium ions and carbonate and bicarbonate ions. Temporary hardness can be reduced by addition of lime. This process is known as lime softening. Also temporary hardness is reduced by boiling the water.
Permanent hardness is hardness (mineral content) that cannot be removed by boiling. When this is the case, it is usually caused by the presence of calcium sulphate and/or magnesium sulphates in the water, which do not precipitate out as the temperature increases. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column.
The calcium and magnesium hardness is the concentration of calcium and magnesium ions expressed as equivalent of calcium carbonate.
Total permanent hardness as CaCO3 = 2.5(Ca2+) + 4.1(Mg2+)
What is Water softener or base exchanger?
Water softening is the removal of calcium and magnesium ion from hard water. To remove calcium and magnesium from source water, ion exchange resin or lime softening is used. In softening, calcium and magnesium ions from hard water get replaced by sodium ions.
For softener, ion exchange resin is used, which is anionic in nature. This resin accepts Ca2+ and Mg2+ ions and gives twice Na+ ions.
After replacement of all Na+ ions with calcium and magnesium ions, the resin needs to be regenerated using NaCl or NaOH.