12. If the UBOD loading to treatment plant is 680kg/d, the per capita water usage is 314Lpcd, servicing a population of 14600 people, (a) What is the influent BOD concentration to the wastewater treatment plant in mg/L ? Assume water loses during usage and in the wastewater collection system amount to 20%. (b) If TWO clarifiers 4.25m deep are to be used to treat the influent wastewater, calculate the required diameter in meters if the retention time is 15 hours. (c) Determine the weir overflow velocity if the water flows through V-notch weirs with 60 bottom angle to a height of approximately 6cm in the weir. (6) [20]