State any three ways of treating polluted water.

Water can be treated in the following three ways:

Primary Treatment: In primary treatment of water, the screens, grit chambers and sedimentation tanks are arranged in a serial order. Water which then passes through them is treated with chlorine gas which kills the harmful bacteria in water. However, in this method dissolved organic matter like salts etc are not treated.

Secondary Treatment: In this method, the organic matter which is present in water is biologically degraded by micro organisms. When primary treatment when water enters a tank, it comes into contact with micro organisms. Air is introduced into the tank through diffusers. Micro organisms in presence of oxygen break the organic matter and the impurities then settle down at the bottom of the tank which are later removed. Then, water is treated with chlorine gas which then kills the rest of the harmful organisms.

Tertiary Treatment: In this method nutrients like nitrogen or phosphorous are removed. This water can be reused for the industrial, agricultural and domestic purposes.