3. A water treatment plant processes 25 MLD of water with the following ionic concentration (in milli equivalent per litre): 0. 4.5 7.5 9.5 Ca Mg Na?+ Other HCO, So? CI 3.0 6.5 9.8 (a) Determine the quantities of chemicals (Kg/day) required to soften this water to the minimum possible hardness by lime soda ash softening. (b) Draw a bar diagram for the finished water. (c) Calculate the dry mass of the solids in the sludge. 4. A rapid sand filter has a bed depth of 0.7 m. It is composed of sand grains that have a specific gravity of 2.65 and a shape factor of 0.82. The porosity of the bed is 0.45 throughout. The sieve analysis of the sand is shown below: Average particle size, mm 1.0 Sieve no: Mass retained % 14-20 0.87 20-28 8.63 0.71 28-32 21.30 0.54 32-35 28.10 0.46 35-42 42-48 23.64 0.38 7.09 0.32 48-60 3.19 0.27 0.23 60-65 65-100 2.16 1.02 0.18 Determine (a) head loss through the bed if the flow rate is 5.0m/s (b) backwash velocity that will just fluidize the largest particles in the bed (c) expanded bed depth