Question

7. Calculate the amount of lime (84%) and soda (92%) required for treatment of 20,000 litres of water, whose analysis is as follows: Ca(HCO3)2 = 40.5 ppm; Mg(HCO3)2 = 36.5 ppm; CaSO4 = 34 ppm; CaCl2 = 27.75 ppm; MgSO4 = 30.0 ppm; SiO2 = 3.5 ppm; NaCl = 10 ppm. Also calculate the temporary & permanent hardness of water sample.

Answer 1

The amount of lime required is 77 kg and the amount of soda required is 81.75 kg.

To calculate the amount of lime and soda required for treatment of 20,000 litres of water, we need to first determine the temporary and permanent hardness of the water sample.

Temporary hardness is caused by the presence of calcium and magnesium bicarbonates (Ca(HCO3)2 and Mg(HCO3)2) in the water. It can be calculated using the following equation:

Temporary Hardness (ppm) = Ca(HCO3)2 + Mg(HCO3)2 = $40.5 + 36.5 = 77 ppm$

Permanent hardness is caused by the presence of calcium and magnesium sulfates (CaSO4 and MgSO4) and chlorides (CaCl2 and MgCl2) in the water. It can be calculated using the following equation:

Permanent Hardness (ppm) = CaSO4 + MgSO4 + CaCl2 + MgCl2 = 34 + $30 + 27.75 + 10 = 81.75$ppm

To calculate the amount of lime (Ca(OH)2) required, we need to use the following equation:

Lime (kg) = (Temporary Hardness (ppm) x Volume (L)) / (2 x 1000 x 100)

Lime (kg) =$(77 x 20000) / (2 x 1000 x 100) = 77 kg$

To calculate the amount of soda (Na2CO3) required, we need to use the following equation:

Soda (kg) = (Permanent Hardness (ppm) x Volume (L)) / (2 x 1000 x 100)

Soda (kg) =$(81.75 x 20000) / (2 x 1000 x 100) = 81.75 kg$

The amount of lime required is 77 kg and the amount of soda required is 81.75 kg.

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