Preliminary and Primary Treatment –II

SOLUTION

1. A rectangular primary sedimentation basin has to be designed for a flow (Q). The influent water contains uniform sized sand particles of settling velocity (v). Show that theoretically, the surface overflow rate (SOR) of the basin required to remove all influent sand particles in the water is numerically equal to the settling velocity (v) of the sand particles.

2. In a primary sedimentation basin, what are effluent launders, and why are they required. Draw a net sketch of such launders.

3. Give three reasons of why even though, theoretically speaking, depth has no effect on the particle removal efficiency in a primary settling tank used in wastewater treatment, a depth of 3-5 m is provided in practice.