Design a sedimentation unit process for a water that contains the following part

Question

Design a sedimentation unit process for a water that contains the following particle size distribution (note that the diameters are logarithmically spaced): The overall process must treat 100,000 liters per day. The design criteria is 85% removal of particle mass, without adding coagulant. Assume the particles are spherical and have a density similar to sand (2.5 g/cm3) and that the water temperature is 10 degree C. Determine the design overflow rate, the number of settling basins and their dimensions. Indicate all necessary calculations to show adherence to accepted design practices. As you are going to be making assumptions and design decisions here (e.g., the number of basins, particle sizes based on reading a graph), answers likely will be different; but you shouldn't be talking to you classmate about this anyway.

Explanation / Answer

Raw water flow per day is 100000 l.

Assume Detention period is 3h.

Volume of tank = Flow x Detention period = 1 x 10^5 x 3/24 = 12.5 m3

Assume depth of tank = 3.0 m.

Surface area = 12.5/3 = 4.16 m2

L/B = 3 (assumed). L = 3B.

      3B2 = 4.16 m2 i.e. B = 1.17 m

       L = 3B = 1.17 X 3 = 3.53 m

Hence surface loading (Overflow rate) = (1 x 10^5) /4.16 = 24,038 l/d/m2

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