(c) If the COD value of the mixture is 0.8xThOD and the mixture represents the composition of an industrial effluent stream flowing into an aeration tank for an activated sludge plant at a flow rate of 933 m/d. Determine the amount of cells that will be produced per day in (16 pts) the plant if the sludge yield coefficient, Yvss/COD = 0.75 6. (b) A mechanical bar screen is to be used in the approach channel with a maximum velocity of 0.64 m/s. The bars are 8 mm thick, and the openings are 12 mm wide, determine: 7. 8. (i) The velocity of water between the bars. (ii) The head loss in meters. (5 pts) (5 pts) You are about to design a new Grit Chamber for a community. Which of the following flow parameters could you use in the designing the unit: Annual Average Daily Flow, Peak Dry Weather Flow, Peak Hourly Flow Rate, Peak Wet Weather Flow, ADWF, AWWF? State the (5 pts) reason for your choice. In a closed system, pyrite (FeS2) dissolves in water and releases ferrous iron, Fe(II), into the system. A biological Fe oxidation process is carried out by iron oxidising bacteria to produce ferric hydroxide, Fe(OH)3(aq). It is determined that oxygen is the principal electron sink. (i) Using information from tables of half reactions (M&E Table 7-6), write a balanced equation for iron and sulphur oxidation and comment on the thermodynamic viability of the equation. (ii) What happens to the sulphur, S, from pyrite under these conditions? (iii) What will be the effect of the reaction on the pH of the solution? ( 8 pts) ( 8 pts) (4 pts) 9. A tank 30 m long, 3 m wide and 4 m deep is operated as a plug flow reactor with contact aeration. Due to the narrow nature of the tank, COD overloaded conditions are observed at the entrance zone of the tank. Concisely describe how you could modify the operation of this tank (10 pts) to avoid the overloaded conditions in the entrance zones. 10. A completely mixed activated sludge process treating a municipal wastewater has a primary clarifier effluent BOD5 of 165 mg/L. The design MLSS is 4000 mg/L, and the MLVSS for the system is 75% of the MLSS. The plant permit is for an effluent BODs of 10 mg/L and 15 mg/L suspended solids. The effluent suspended solids contribute 0.5 mg BOD5/mg suspended solids in the final effluent. The Monod kinetic parameter values obtained at an ambient operating temperature of 24C are max = 3.0 day, Ks = 60 mg/L, Y = 0.60 mg MLVSS/mg BODs degraded, ka = 0.06 day, and the influent flow is 18.9 MLD. Under the above given conditions, determine: (a) The cell residence time (SRT) assuming cell growth in the reactor follows Monod (12 pts) kinetics and mixed order substrate uptake rate. (b) The required hydraulic retention to meet the given effluent conditions, HRT. (8 pts) Page 3 of 6