You are evaluating the usefulness of an existing primary clarifier of a 25 MGD drinking water treatment plant to remove sand grains from a Willamette River source water. The existing center-fed circular clarifier is 3 meters deep and has a radius of 5 meters. The average sand particle density in the source water is 1,100 kg/m3 . The average water temperature is 20o C which leads to an average viscosity of 1 g/(m*s) and an average density of 998.2 g/L. 1) What is the critical settling velocity for this clarifier (in meters/second)?
2) What is the diameter (in mm) of the largest sand grain particles leaving the clarifier? (Assume that all sand grains have the same density)