A water treatment plant has a primary sedimentation basin that processes 400 m3 /h of water. The basin is rectangular and has a depth of 4 m, width of 6 m, and length of 36 m. The temperature of the water is 20 °C. Use Appendix C in your book (and posted on Blackboard with this assignment) to find the exact values of density and viscosity for water at this temperature.

(a) (10 pts) What is the hydraulic residence or detention time (O) of the tank in hours?
(b) (10 pts) What is the critical settling velocity, vo, for this tank in m/s?
(c) (10 pts) For sand (silica) particles with a density of 2650 kg/mº, determine the particle diameter in mm that corresponds to the critical settling velocity from part (b). (
(d) (5 pts) There are particles entering the primary sedimentation basin that are smaller than the diameter you calculated in part (C). Briefly describe (in one or a few sentences) a process that can be used after the primary sedimentation basin to remove these smaller particles.