Chemistry (3 semester)

                      WATER TREATMENT(Class 1)

•Water is present in liquid, solid and gas state.

•It is important for living organisms.

Sources of water

1)Surface water

a) Flowing water(River, Stream)

b)Still water(Lakes, Ponds, Reservoirs)

2) Underground water(springs, wells, tubewells)

3)Sea/Oceans

4) Rainwater

Water can be divided into two types

1)Hardwater

•Ca+2/Mg+2 is present in the form of bicarbonates.

•It does not form foam easily.

2)Soft water

•The water which produces foam easily with soap or detergent.

•It does not contain ions.

Different kinds of impurities in water

1) Physical impurities

•Coloured water due to presence of suspended particles, ions, salts, slits, etc.

•Taste(brackish/bitter)

•Odour

2) Chemical impurities

a) Organic impurities

detergent, pulp, vegetables, dead animals

b) Inorganic impurities

These are chemical impurities.

3)Biological impurities

Bacteria, fungi, virus, algae

Types of hardness

1) Temporary hardness

•Due to presence of bicarbonates.

•It can be removed by boiling as bicarbonate are unstable and get converted into carbonates which are stable compounds.

•These carbonates are insoluble in water and get precipitated in the form of scum.

2) Permanent Hardness

•It is due to presence of chlorides, sulphates and carbonates.

•It is removed by chemical treatment.

                  

                             CLASS-2

The concentration of hardness as well as non hardness constituting ions are expressed in terms of equivalents of calcium carbonate because it ham molecular weight of 100 and equivalent weight of 50 which permits the multiplication and division of concentration when required. It is the most insoluble salt that can be precipitated during water treatment.

Equivalent of CaCo3= 

(Mass of hardness producing substance×Chemical equivalent of CaCo3)/Chemical equivalent of hardness producing substance.

=(Mass of HPS×50)/ Chemical equivalent of HPS

Unit of hardness

1)•ppm (parts per million)- 1 part of CaCo3 equivalent in 10^6 parts of water.

•Mg/ litre- 1 mg of CaCo3 equivalent in 10^6 mg of water.

2) Clark's Degree

•Number of grains (1/7000 lb) of CaCo3 equivalent hardness per gallon (10 lb).

• It is a part of CaCo3 equivalent of hardness per 70000 gallon of water.

•1° Cl= 1 part of CaCo3 equivalent hardness per 70000 parts of water.

Disadvantages of hardness

1) Domestic uses

•Washing

•Bathing

• Cleaning

•Drinking

•Cooking

•For washing and cleaning purpose we use soap .

The formation of scum makes the washing process difficult  as it got stuck on the material and it also leads to difficulty in formation of leather.

•If we drink Hardwater, then this may leads to formation of stone's in body.

•During cooking with Hardwater, the boiling point increases due to presence of ions. This lead to more fuel consumption.

2) Industrial Uses

•Textile industry

Soaps are used for removing extra products from textile and if water is hard then this lead to uneven cleaning.

•Paper industry

•Sugar industry

•Dyeing industry

•Concrete industry

•Pharmaceutixal industry

•Boiler feed water

Water is used for generation of steam in various industries.

And also used for cooling purpose.

Problems during consumption of Hardwater

1)Sludge- During boiling water  is heated and  get evaporated due to which concentration of salts increases which leads to formation of sludge and scales.

•Sludge are soft, loose and slimey particle present in water.

•Some salt form sludge at low temperature and some salts form sludge at high temperature.

•Sludge can be easily scrapped of with wire brush. It is formed in colder portion of the boilers and gets collected in the area where the flow rate is slow and in the bent areas.

•Sludge formation takes place by the substances which have greater solubility in hot water then in cold water.

Example- CaCo3, MgCl2, MgCo3, etc.

•Prevention of sludge formation-

1)By using soft water

2)Blow down operation- After the formation of steam 2 to 3 times, the old water is removed and boiler is filled again.

2)Scale- Scales are the hard deposits which stick very firmly to the inner wall of the boiler.

 

These are very difficult to removed even with the help of hammer and chisels.

•Reason for formation of scale

a) Decomposition of calcium bicarbonate during boiling process.

b) Hydrolysis of Magnesium chloride

Calcium bicarbonate scale is harder then magnesium hydroxide scales.

c)Presence  of silicas

It get deposited as CaSiO3 and MgSiO3.