Rework Problem 4-21 using caustic soda instead of lime. Soften the water to the lowest h...

Rework Problem 4-21 using caustic soda instead of lime. Soften the water to the lowest hardness that can be achieved with caustic alone. Assume the caustic is 100% pure, CO₂ concentration = 9.96 mg/L, and that an excess of 40 mg/L of caustic will be added.

Problem 4-21

Determine the lime and soda ash dose, in mg/L as CaO and Na₂CO₃ , to soften the hames River water to a final hardness of less than 125 mg/L as CaCO₃. Assume that all the lkalinity is bicarbonate and that the lime is 90% pure and the soda ash is 97% pure.