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ENG 4051 Water & Wastewater Engineering –
UG CHEM ENG 7035 Water & Wastewater Engineering – PG Reading Time Writing Time Total Duration 10 mins 120 mins 130 mins Questions Time Marks Answer 120 mins 100 All questions INSTRUCTIONS TO CANDIDATES: 1. It is recommended that you spend 10 minutes reading this paper. 2. This is an OPEN BOOK examination. 3. Maximum Mark = 100. Marks for each question are shown. 4. Answer ALL six questions. 5. Write your name and student number on all loose diagrams. 6. Submit all answer papers in ONE PDF file. 7. This must be your own work. Any similarity to other student’s work will result in zero for the question. 8. Any materials than may be help with answering the questions are allowed Student name: Student ID: 2 Question 1 [15 Marks] Distinguish among dissolved substances, suspended solids and colloidal substances in water based on (1) their size, and the commonly used (2) measurement methods, and (3) treatment units by which they can be removed from the water. Question 2 [20 Marks] What is the purpose of coagulation and flocculation? Describe the process from coagulation to floc formation, and the operation parameters that affect the coagulation and flocculation process. Question 3 [15 Marks] Briefly describe the similarity and difference of following terminologies used for water quality and water/wastewater treatment. 1). Conductivity and total dissolved solids 2. Anoxic and anaerobic digestion processes. 3. Disinfection and sterilization processes Question 4 [15 Marks] Determine the BODu and BOD5 (in mg/L) of a mixture of 150 mg/L glucose (C6H12O6) and 150 mg/L glutamic acid (C5H10N2O3), Assume the value of BOD5 first order reaction rate constant is 0.23 d-1 (base e) at 20 oC. Question 5 [15 Marks] Effluent discharged from an industrial process contains grit particles with an average size of 0.08 mm and a specific gravity of 2.65.
To remove the particles you are required to design a horizontal grit chamber that is 13.5 m in length and 0.56 m in width.
Will these particles be collected in this horizontal grit chamber if the effluent is treated with a
flowrate of 0.15 m3/s and horizontal velocity of 0.25 m/s in the grit chamber? Assume: (1) the viscosity of the effluent is 0.955 m Pa·s, and (2)
water density is 1000 kg/m3 at 22 oC. 3 Question 6 [20 Marks] An activated sludge system is designed to treat a 6000 m3/d
wastewater with an influent BOD concentration of 120 mg/L and sludge retention time of 6 d.
The activated sludge system will be operated for 90% BOD removal with an observed yield of 0.7 mg cells/mg BOD utilised.
It is expected that the effluent from the activated sludge system contains 10 mg/L of BOD,
2500 mg/L of MLVSS and 3000 mg/L of MLSS. Determine 1. the aeration tank volume in m3,
2. the amount of sludge produced daily in kg MLSS/d, and 3. the hydraulic retention time of the activated sludge system
4. the ratio of food to microorganisms in the aeration tank. END OF EXAM