Question

A sample of water contains following impurities :
Mg(HCO3)2 =73 mg/lit , MgSO4 = 120 mg/lit , CaCl2 = 222 mg/lit and Ca(NO3)2 = 164 mg/lit . The purity of lime is 74% and soda is 90% . Calculate the quantity of lime and soda needed for softening of 50,000 litres of water .

Answer 1

Impurities (mg/lit)	Multiplication Factor	CaCO3 equivalents (mg/lit)	Requirement
Mg(HCO3)2	100/146	73 x 100/146 =50	2L
MgSO4	100/120	120 x 100/120 =100	L + S
CaCl2	100/111	222 x 100/111 =200	S
Ca(NO3)2	100/164	164 x 100/164 =100	S

Lime Requirement = 74/100 x [CaCO₃ equivalent of 2x Mg(HCO₃)₂ + MgSO₄ ] 
= 74/100 x [100 + 100 ]
=148 ppm .
Lime Required for 50,000 litres of water with 74% purity
= 148 x 50,000 x 100/74
= 10,000 gm .
Soda Requirement = 106/100 x [CaCO₃ equivalent of MgSO₄ + CaCl₂ + Ca(NO₃)₂ ] 

= 106/100 x [100 + 200 + 100 ]
= 424 ppm .
Soda Requirement for 50,000 litres of water with 90% purity
=424 x 50,000 x 100/90
= 23,556 gm .
The Lime Requirement is 10,000 gm and Soda Requirement is 23,556 gm .