13. For a municipality with a population of 6400 persons, a treatment plant utilising rotary biological contactors (RBCs) is suggested. Pertinent data are: Average water usage per person Two parallel treatment flow train Influent BOD5 BOD5) Effluent BODS Number of stages k value 380 L/cap-d [See figure below] 400 mg/L, (primary clarifier removes 33% of the 15 mg/L 4 50.2 L/d-m from a pilot study Clarifier RBCs Channel A Influent, Q Clarifier RBCs Channel B Figure 1 (a) Determine the calculated design hydraulic loading (q), L/day-m. ( 8 pts) (b) Determine the BODs after each stage, mg/L. (4 pts) (c) Determine the disc area per stage, m. (6 pts) (e) If the third stage of Channel A fails, determine how much water could be safely diverted to Channel B while maintaining the effluent BODs to the permitted value of 15 mg/L in both channels. (16 pts) (f) Provide a design of an overflow tank (size and operational schedule) for the system if the failure conditions occur periodically at least five times a year and each failure event last 7 days during which time repairs are successfully affected. (10 pts)