Calculate quantities of lime and soda required for softening of 20,000 litres of water containing following salts in ppm (16.4 ppm NaAlO2 used as a coagulant) Ca+2 = 160 ppm Mg+2 = 72 ppm HCO3 – = 73.2 ppm CO2 = 44 ppm Al2(SO4)3 = 34.2 ppm HCl = 36.5 ppm.a.Lime = 7.84 mg, Soda = 15.05 mgb.Lime = 7.84 g, Soda = 15.05 gc.None of thesed.Lime = 7.84 kg, Soda = 15.05 kg
Question
Calculate quantities of lime and soda required for softening of 20,000 litres of water containing following salts in ppm (16.4 ppm NaAlO2 used as a coagulant) Ca+2 = 160 ppm Mg+2 = 72 ppm HCO3 – = 73.2 ppm CO2 = 44 ppm Al2(SO4)3 = 34.2 ppm HCl = 36.5 ppm.a.Lime = 7.84 mg, Soda = 15.05 mgb.Lime = 7.84 g, Soda = 15.05 gc.None of thesed.Lime = 7.84 kg, Soda = 15.05 kg
Solution
To calculate the quantities of lime and soda required for softening of water, we need to consider the amount of each salt present in the water.
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Lime requirement: Lime is used to remove the hardness caused by Ca+2, Mg+2 and CO2. The requirement of lime is calculated as follows:
For Ca+2: Lime required = 74/100 * ppm of Ca+2 = 74/100 * 160 = 118.4 mg/l For Mg+2: Lime required = 112/100 * ppm of Mg+2 = 112/100 * 72 = 80.64 mg/l For CO2: Lime required = 56/44 * ppm of CO2 = 56/44 * 44 = 56 mg/l
Total lime required = 118.4 + 80.64 + 56 = 255.04 mg/l
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Soda requirement: Soda is used to remove the non-carbonate hardness caused by Ca+2, Mg+2 and Al2(SO4)3. The requirement of soda is calculated as follows:
For Ca+2: Soda required = 106/100 * ppm of Ca+2 = 106/100 * 160 = 169.6 mg/l For Mg+2: Soda required = 151/100 * ppm of Mg+2 = 151/100 * 72 = 108.72 mg/l For Al2(SO4)3: Soda required = 106/100 * ppm of Al2(SO4)3 = 106/100 * 34.2 = 36.252 mg/l
Total soda required = 169.6 + 108.72 + 36.252 = 314.572 mg/l
Now, to calculate the total amount of lime and soda required for 20,000 litres of water, we multiply the per litre requirement by 20,000.
Total lime required = 255.04 mg/l * 20,000 l = 5100.8 g or 5.1 kg Total soda required = 314.572 mg/l * 20,000 l = 6291.44 g or 6.291 kg
So, the correct answer is not listed in the options provided. The correct quantities are Lime = 5.1 kg and Soda = 6.291 kg.
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