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Match the water purification stages in Group-I with the corresponding items in Group-II
Group I Group II P. Coagulation 1. Ammonium hydroxide Q. Filtration 2. Sodium Zeolite R. Disinfection 3. Alum S. Softening 4. Sand 5. Chlorine
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- P-3, Q-4, R-1, S-5
- P-1, Q-4, R-3, S-2
- P-2, Q-3, R-5, S-4
- P-3, Q-4, R-5, S-2
Correct Option: D
P-3, Q-4, R-5, S-2
⋅ Clarification (coagulation, flocculation, sedimentation and sludge removal) refers to the separation of particles such as dirt, organic matter, etc. from the water stream. One of the first steps in a conventional water purification process is the addition of inorganic coagulants or chemicals to assist in the removal of or ganic and inor ganic particles suspended in water and contributing to its turbidity and color. Chemical addition, i.e. aluminium sulphate or alum, destabilizes the particle charges and prepares them for clarification either by settling or floating out of the water stream. Flocculation refers to the process by which fine particulates are caused to clump together under natural processes such as Brownian motion and through induced mixing into a floc (amorphous metal hydroxides). The floc may then float to the top of the liquid (creaming), settle to the bottom of the liquid (sedimentation), or be readily filtered from the liquid. Water exiting the flocculation basin enters the sedimentation basin, allowing floc to settle to the bottom.
⋅ Sand Filtration uses Sand, anthracite or activated carbon filters to refine the water stream (from which floc has been separated) removing smaller particulate matter and any unsettled floc. Most common type is a rapid sand filter. Slow sand filters are used when larger area is avaliable as the water must pass very slowly through the filters and the filters rely on the biological processes. The filters are constructed using graded layers of sand, with the coarsest sand at the bottom and finest sand at the top.
⋅ Disinfection via chlorine addition is the most common method in use. Chlorine being a strong oxidant, effectively kills bacteria and most viruses and maintains a residual to protect the water supply through the supply network.
⋅ Softening: Sodium zeolite is an ion exchange resin used for water softening (where Ca2+ and Mg2+ ions are replaced with Na+ or K+ ions) and for removal of toxic ions such as nitrite, lead, mercury, arsenic and others.
