The presence of organic matter, algae, dissolved hydrogen Sulphide and contamination due to industrial wastes containing phenol, excessive chlorine, etc. and dissolved iron and manganese salts impart color, odor and taste to the water. Following are some important water treatment methods employed for removing color, taste and odor.
Aeration is the process of bringing water in intimate contact with air. During the process, water absorbs oxygen from the air. Aeration removes iron, manganese, CO,. H2S and oxidize certain organic impurities present in the water. Up to certain extent bacterias are also killed. However, it can remove CO2 up to 10% only and residue to the extent of 3-5 mg/liter always remains in water.
Note: Excessive aeration should not be done ; otherwise excessive absorption of oxygen by water increases its corrosive characteristics and it may the need ‘DE-aeration’ of water.
Activated carbon is obtained by charring wood or saw dust at 500°C in a closed vessels, thereby hydrocarbons, which usually interfere with the absorption of organic matters, are expelled. It is available in granular or powdered from. As it is highly porous and possesses free valencies ; both properties provide it the high adsorption capacity.
Activated carbon is most widely used for the removal of tastes and odors from the public water supplies, because it has excellent properties of attracting gases, finely divided solid particles and phenol type impurities. The activated carbon, usually in the powdered form, is added to water either before or after the coagulation with sedimentation. But it is always added before filtration. Feeding devices are similar to those used in feeding the coagulants.
Copper sulphate (CuSO4.5H20′ solution is usually applied with dose of 0.5 to 0.75 mg/liter to the treated water, just before it is allowed for distribution in the mains It can also be added in the lakes or reservoirs. Cropper sulphate helps in removing odors, tastes and colors from the water. Its main advantage is that it cheeks the growth of algae, even before production and also kills some bacterias.