A moderate amount of total BOD can be removed in a primary clarifier through settling. The relationship between percent removal of total BOD and the surface overflow rate in a circular clarifier can be described by the following straight-line equation:

 y = 42 – 0.255x where y is the percent removal of total BOD and x is the overflow rate in m/d. The average wastewater flow rate is 5000 m3/d. Calculate the diameter of the clarifier that would result in removal of one-third of the total BOD. Also, calculate the detention time in the primary clarifier when the sidewall depth is 3.6 m.