A batch settling test has been performed on a chemically coagulated flocculant w

Question

A batch settling test has been performed on a chemically coagulated flocculant wastewater having an initial suspended solids concentration of 480 mg/L, to develop criteria for the design of a primary clarifier. The test column was 140 mm in diameter and 2.40 m high, with sampling ports spaced every 0.6 m. The suspended solids remaining at the noted sampling times are given in Table 1. Using a graphical approach, size a circular primary clarifier (area, diameter and depth) for 50% solids removal at an influent flow rate of 4000 m^3/d.

Explanation / Answer

Solution:-

Detention period: for plain sedimentation: 3 to 4 h, and for coagulated sedimentation: 2 to 2 1/2 h

Velocity of flow: < 18 m/h (horizontal flow tanks)Tank dimensions: L : B : 3 to 5 : 1   
Generally L = 30 m (common) maximum 100 m.Breadth: 6 m to 10 m.

Circular:Dia< 60 m, Generally 20 to 40 m

Depth 2.5 to 5.0 m (3 m)

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