Miscellaneous Water Treatment

• WATER SOFTENING: 

Removal of hardness from water is known as Water softning.

Removal of Temporary Hardness:

1. by boiling
2. by adding lime

Removal of permanent hardness:

1. Lime Soda Process
2. Zeolite Process
3. Demineralization Process (or) Deionization Process):

Lime Soda Process: Lime (Ca(OH2) and Sodium carbonate [Na2CO3] (or soda ash) are used to removal permanant hardness from water.

Quick lime CaO, or hydrated lime Ca(OH)2 can be used for water softening.

Lime Soda Water Softening plant consists of the following units:

1. Feeding and mixing devices
2. Settling tank or settling basin
3. Recarbonation plant.
4. Filters

Recarbonation plant: Carbon dioxide CO2 gas is diffused through the effluent so that the insoluble calcium carbonate and magnesium hydroxide combine with carbon dioxide to again foms the soluble bicarbonates of calcium and magnesium

Advantages of Lime-Soda Process:

1. Economical
2. pH value increases arid corrosion of the distribution system decreases
3. he process is suitable for turbid, chalybeate and acidic waters for which zeolite process cannot be used
4. quantity of coagulant will be required for coagulation.
5. removal of iron and manganese to some extent.
6. here is likelihood of killing of pathogenic bacteria in this process.
7. Better for excessively hard waters.

 Disadvantages of lime-soda Process:

1. A large quantity of sludge is formed  in this process which needs to be disposed off by some suitable method
2. In this process recarbonation is required by Lime soda process water of zero hardness cannot be produced.

Zeolite Process: 

• Zeolite is a complex compound of aluminium. silica and soda
• Hard water is passed through a bed of ion exchange material or ion commonly known as Zeolite
• Calcium and magnesium are removed from water as these are substituted b sodium by ion- exchange process
• By Zeolite process the hardness of water is reduced almost to zero.

Advantages of Zeolite process:

1. Sludge is not formed and there is no problem of sludge disposal.
2. Does not require any skilled supervision.
3. His possible to reduce hardness of  water to zero. This is useful for softening of water to be used for boilers and certain textile industries.

Disadvantage or zeolite process:

Cannot be adopted for highly turbid water

Demineralization Process or Deionization process: It is similar to zeolite process with the difference that in demineralization process the metallic ions viz,calcium magnesiurn. etc. are exchanged for hydrogen ions. The ion exchanger is prepared with carbonaceous material or resin. The effluent obtained in the demineralization process is free from minerals and it has a quality almost equal to that of distilled water used for industries

Removal of  Colour, Odour and taste:

1. Aeration
2. Treatment by activated carbon
3. Use of Copper sulphate.

Aeration: it is a process in which water is brought in intimate contact with atmospheric air to promote exchange of gases between water and atmospheric air.

1. Carbon dioxide, hydrogen Sulphide and other volatile substances imparting taste and odour to water are easily expelled
2. Iron and manganese present in water are oxidized to certain extent by aeration.

Treament by activated  carbon: Activated carbon is used to remove colour, taste mid odour from water. It is available  granular as well as powder form.

Activated carbon is used to remove organic contaminants from water by the process of adsorption.in

adsorption high surface area is the prime consideration.

Activated carbon can be applied for treatment of water in two ways

• As filter media
• As fine powder feed

Use of copper sulphate:

• removal of colour ,odour & taste from water

Iron and manganese: often occur together in groundwater but manganese usually occurs in much lower concentrations than iron. Both iron and manganese are readily apparent in drinking water supplies. Both impart a strong metallic taste to the water and both cause staining.

Fluoridation and Defluoridation:

Fluoridation: Water fluoridation is the controlled addition of fluoride to a public water supply to reduce tooth decay. Fluoridated water contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride.

Defluoridation: is a treatment used to remove fluoride from drinking water. The process of this technique is to remove fluoride, which is a highly toxic chemical, to prevent health issues and dental issues that contains in humans. It is suppose to help save the environment so people can drink safe water

DESALINIZATION OR DESELINATION:

Distillation: is a method of separating mixtures based on differences in their volatiles in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction. Commercially, distillation has a number of applications.

Reverse osmosis: a process by which a solvent passes through a porous membrane in the direction opposite to that for natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure

Electrodialysis (ED): is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. This is done in a configuration called an electrodialysis cell.

Freezing: Temperature of saline water is gradually lowered until ice crystals are formed. These are free of salt and can be separated. The ice crystals when melted gives fresh water.

Demineralization: Salts are removed from water through the use o)’ ion exchangers.

Solar evaporation: Solar energy is utilized to convert saline water to fresh Water.

Procedure to calculate Chemicals requirement in lime-soda process:

Method-I: Approximate Procedure

This procedure is used when hardness is given as CaCo3

Calculate lime requirement based on Total hardness :

• Lime as CaO required (mg/I) = TH x 56/100
• Soda required (mg/I) = NHC x 106/100