Problem 4. The physicochemical properties of a surface water is given in Table below: The surface water with 6000m3/d of flow rate will be treated for hardness removal using lime-soda softening which involves increasing the pH above 10 using slake lime (Ca(OH)2 or portlandite) and adding calcium bicarbonate (Ca(HCO3)2) salt. Ca(HCO3)2 salts required to obtain hardness removal by at least 90%. (25p)