POKHARA UNIVERSITY
Level: Bachelor
Programme: BE
Semester – Fall
Course: Sanitary Engineering
Year : 2009
Full Marks : 100
Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
1. a.
Define Dry weather flow (DWF). Describe in detail the various factors affecting the quantity of sanitary sewage. b.
Calculate the diameter of combined circular sewers for the following data:
Rate of water supply = 375 lpcd, population density = 160/hec, peak factor = 1.5, area = 5000 hectare intensity of rainfall = 0.5mm/hrs inverted slope of sewere = 1 in 800, impervious factor = 0.95 and
Manning's co-efficient of rugosity n = 0.013. The sewer should run half full during peak flow condition.
2. a.
Describe nitrogen and phosphorous cycle of decomposition. b.
The BOD of a sewage sample measured at 2 and 8 days are 125.00 mg/1 and 234.78 mg/1 respectively. Calculate rate reaction constant, k and 5-days BOD.
3. a.
What do you understand by self-purification of streams? Describe the various factors affective the self-purification of a stream. b.
An industry is discharging its sewage of 100 lit/sec with ultimate
BOD of 1500 mg/1 and DO of zero into a river with a discharge of
10,000 litres/sec ultimate BOD of 5 mg/1 and DO of 9 mg/1 calculate BOD at critical point. Assume saturation DO in the river just after mixing with sewage = 9.5 mg/1, deoxygenation constant with base 10=0.1/day and self purification constant = 5.
4. a.
What are the advantages of re-circulation in high rate tricking filter? b.
Calculate the effluent BOD of a two stage tricking liter with the following data:
Flow = 4000m 3 /day, BOD after primary treatment = 250mg/l. volume of filter l = 600m 3 , volume of filter 2 = 300 m 3 and recirculation ratio for both filters = 1:5.
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5. a.
Describe aerobic and anaerobic sludge digestion. b.
Design a septic tank for 200 persons. Assume any other data as per requirement.
6. a.
What are the method of solid waste disposal? Describe any two methods. b.
A sewage has suspended solid contains 250mg/l. The sedimentation tank revome 55% of the suspended solid and water content of the sludge is 95%. Determine the volume of sludge produced in the sedimentation tank after treating 6.5 million litres of sewage. Assume specific gravity of sludge = 1.02
7. Write short notes on (Any Two) a.
Flushing tank as sewer appurtenance b.
Grit chamber c.
Leaching cesspool
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