Water and Sewage Treatment Process

Sewage is referred to waste from the bathrooms and kitchens of households.
Water is treated for making it fit to drink for human consumption.

The three stages of treatment are:

1. Primary Treatment
a. Screen Filtration
       Large and visible impurities are removed from water/sewage by passing it through mettalic screens of
       decreasing sizes. Items such as small gravel, pieces of leaves, etc are filtered through this method.

 b. Sand Filter
    Water/sewage is then passed though a sand filter to remove particles of very small sizes. The sand is generally compacted very tightly in the filter and does not allow any undissolved particles to get through it.

2. Secondary Treatment
    Generally water contains dissolved salts (inorganic impurities) and also fats and oils (organic impurities)
   
To get rid of dissolved salts, Reverse Osmosis (R.O.) technoloy is used. Chorides and carbonates of soduim, calcium and magnesium are removed through the R.O technology. Incase water with almost zero dissolved salts is desired then a De-Mineralization plant would have to used. This plant is generally used for boiler water but not for human consumption.
   
 To get rid of dissolved fats and organic matter, water is allowed to stand still and bacterial growth is allowed which eats away the organic matter and then settles at the bottom of tank as sludge.
Infact alum is added to the tank which encourages the sludge particles to stick together by a process called flocculation and settle at the bottom of tank.
Clarified water is then obtained from top of the tank.

3. Tertiary treatment
     Clarified water still contains bacteria and viruses which can make humans sick. Hence the clarified water is then chlorinated or treated with ozone to get rid of the pathogens.
At homes we use UV rays in the Aquagaurd to achieve the same effect.

Note:
Technolgies are being developed to convert sludge into bio-gas as sludge is rich in organic matter.