Question

determine using split treatment the lime and soda ash dose,in mg/L as CaCO3 to soften the following water to final hardness of 80mg/L as caco3 .

if the price of lime purchased as CaO is 100$ per megagram and for soda ash purchased as Na2CO3 is 200$ per mega gram

what is the annual chemical cost of treating 0.5 m3/s of ths water ?

assume lime is 93% pure and soda ash is 95% pure

given

calcium(ca+2) =200mg/L as CaCO3

maganisum (Mg+2) =100mg/L as CaCO3

(HCO3- =150mg/L as CaCO3

CO2 =22mg/L as CaCO3

use split treatment

Answer 1

Lime dosage = The carbon dioxide as CaCO3 + The total hardness + Magnesium concentration

= 22 + 80+ 100 = 202 mg/L

Soda ash dose = (Non carbonate hardness as CaCO3 * Calcium as carbonate) / Mg = 150*200/100 = 300mg/L

density of water in grams/m3 = 998000 grams/m3

Mass of water = 998000(grams/m3) * 0.5(m3/s) = 499000 grams/s

We need 502grams of lime and soda ash dose of treating the water. So 3$ of lime and soda ash dose needed for treating the water.