Which of the following treatments reduce salinity of water?
(i) Flocculation and sedimentation.
(ii) Filtration.
(iii) Reverse osmosis.
(iv) Electrodialysis.

Select the correct answer given below.

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JKSSB JE (Civil) Official Paper (Held On: 19 Nov, 2023)

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Answer 1

Explanation:

Salinity Reduction (Desalination)

Salinity in water refers to the concentration of dissolved salts, primarily chlorides, sulfates, sodium, and other ions. Removing these requires advanced treatment processes capable of separating dissolved ions.
Reverse Osmosis (RO) is a membrane-based process where water is forced under pressure through a semi-permeable membrane.
It effectively removes dissolved salts, heavy metals, and other impurities.
Widely used for desalination of seawater and brackish water.
Electrodialysis uses ion-exchange membranes and electric potential to remove dissolved ions from water.
Positively and negatively charged ions migrate through membranes to separate chambers, leaving behind desalinated water.
Effective for saline groundwater and industrial wastewater.

Additional InformationPrimary Treatment of Water

Removal of Large and Settleable Solids
Primary treatment involves physical processes like screening and sedimentation to remove floating debris, grit, and suspended solids. Large solids are first removed by bar screens, followed by grit chambers to eliminate heavier inorganic matter such as sand and gravel.
Sedimentation for Suspended Solids
In primary sedimentation tanks, water is held for several hours to allow heavier suspended particles to settle at the bottom as sludge, while lighter materials like oils and grease float to the surface for removal. This reduces the total suspended solids (TSS) load entering secondary treatment.
Partial Reduction of Organic Load
Though not designed to remove dissolved contaminants, primary treatment helps in reducing the organic load (BOD) by about 25–30%, making downstream biological processes more efficient. It also stabilizes the flow and composition of wastewater.
Sludge and Scum Handling
The settled sludge is collected and sent for further treatment like thickening or digestion. The floating scum, consisting of oils and grease, is skimmed off separately. Proper handling of these by-products is crucial to prevent blockages and maintain operational efficiency.