3312- 83 Part I. Write a short note on the Event Tree Analysis (ETA) by sketching a neat flowsheet diagram describing the process. Part II. An activated sludge treatment process with an aeration tank capacity of 4000 m is to be used to treat wastewater having a flow of 500 m/hr. Assuming the biomass decay rate (Ka) in the cell growth rate equation (rg) as zero, and given that the concentration of MLSS is 2000 mg/l; yield coefficient (Y) = 0.5; inlet substrate concentration of the activated sludge treatment process is 300 mg/l; maximum specific growth rate (k)= 0.4 / day, and saturation constant (Ks) = 5 mg/L. Find the hydraulic retention time (HRT), mean cell residence time substrate (Se) from the secondary clarifier. (Hint: Use the equations derived for the HRT and MCRT provided in the lecture slides for your calculations). [5+5=10 marks] 2-202