Test: Water Softening - Civil Engineering (CE) MCQ

The rinse water contains calcium or magnesium ions which form insoluble salts and leaves a coating of insoluble stearates on tub and shower surfaces, commonly called soap scum, in hard water areas.

Softening is the removal of calcium, magnesium and certain other metal cations in hard water. The product water that is soft water extends the life of plumbing.

Lime softening is the process in which lime is added to hard water to make it softer. It has several advantages over the ion-exchange method but requires full-time, trained personnel to run the equipment.

The methods such as reverse osmosis, ion exchange resins and chelating agents are used to remove hardness. Sedimentation can be used to remove suspended solids.

Citric acid is used to soften water in soaps and laundry detergents. A commonly used synthetic chelator is ethylenediaminetetraacetic acid (EDTA).

Ion exchange resins are usually organic polymers. It contains anionic functional groups to which divalent cations bind strongly than monovalent cations.

Magnesium load= Magnesium as CaCO₃ x Flow rate x Operating hours/1000. Resin Volume= Magnesium load/ (Exchange capacity x Correction factor). Resin Volume =[(80 x 135 x 20)/1000]/(47 x 0.9)= 5.1 m³.

A commonly used synthetic chelator is ethylenediaminetetraacetic acid (EDTA). Chelators are used in chemical analysis, as water softeners and are ingredients in many commercial products such as shampoos and food preservatives.