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Enrolment No.GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-VII (NEW) EXAMINATION - WINTER 2018
Subject Code: 2171306
Subject Name: Wastewater Engineering
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Time: 10:30 AM TO 01:30 PMInstructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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Q.1 (a) Explain the importance of Equalization process in a wastewater treatment plant. 03
(b) Explain the purpose of following unit operations/processes in a wastewater treatment plant : (i) Screening (ii) Suspended growth biological process (iii) Primary sedimentation (iv) Nitrification 04
(c) Differentiate between domestic wastewater and industrial wastewater. 07
Q.2 (a) Explain the terms : (i) SOR (ii) WOR (iii) Food to microbe ratio 03
(b) Design an aerated grit chamber for an average flow of 8 MLD. 04
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(c) A coarse screen is inclined at angle of 60" to the horizontal. There are 25 numbers of rectangular bars having 20mm size (facing the flow) and a clear spacing of 25mm. Determine the head loss using Kirschner equation, when the bars are clean and approach velocity is 1 m/s. 07OR
(c) Find out the area of secondary clarifier to be used for ASP using following data, if the sludge has to be thickened to a concentration of 10,000 mg/L
| Kg/m3 | 80 | 60 | 50 | 40 | 30 | 20 | 10 | ||
| MLSS | 4 | 3 | 2 | ||||||
| Velocity m/d | 0.44 | 0.78 | 1.7 | 53 | 34 | 62 | 68 | 76 | 83 |
Q.3 (a) Enlist and explain the operational problems of screens. 03
(b) Write a short note on tube settlers. 04
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(c) Design a primary settling tank for a wastewater treatment plant having a flow rate of 0.5 m3/s assuming SOR value as 32.5 m3/m2-day. Check for WOR and detention time. 07OR
(a) Draw a flow diagram for sewage treatment with suspended growth biological process. 03
(b) Enlist the different types of mixers used in a wastewater treatment plant and explain any one. 04
(c) Design a cylindrical flash mixing tank by determining the tank dimensions and required input power using following data :
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Design flow rate = 11.5x 106 m3/dRapid mix t=35's
Rapid mix G =600s-1
p=1.5195x 10-3 N/ m2—s 07
Date: 29/11/2018
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Total Marks: 70Q.4 (a) Explain the operational problem of Bulking sludge. 03
(b) Differentiate between diffused aeration and mechanical aeration 04
(c) For a flow rate of 0.05657 m3/s and average BOD5 concentration of 140 mg/L in primary treated effluent , find the volume of aeration tank for a complete mix ASP for following conditions : 07
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- The treated effluent should have 30 mg/L BOD and 30 mg/L SS
- Assume BOD of SS =33 % of SS
- Ks=100 mg/L BOD, µm=2.5 d-1. Y =0.5, kd=0.05d-1
OR
(a) What is Bio tower? Explain its working. 03
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(b) Write a short note on Sequencing Batch Reactor 04(c) Design a Rotating Biological Contactor to treat a flow of 50 MLD of primary treated wastewater having BOD5 of 200 mg/L. Desired effluent BOD5 is 30 mg/L. 07
Q.5 (a) Prepare a list of sludge dewatering devices and explain any one along with a neat sketch. 07
(b) Determine the dimensions of UASB reactor for wastewater having flow rate of 1500m3/d. The characteristics of wastewater are as under: 07
BOD = 300 mg/L
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COD= 450 mg/LTSS=400 mg/L
VSS=270 mg/L
Sulphate = 85 mg/L
Assume required data.
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Also estimate the methane gas generation rate.OR
(a) Differentiate between Standard rate and high rate digester. 03
(b) Design an oil and grease trap to remove 170 mg/L of O& G for a flow of 45000m3/d of domestic wastewater. 04
(c) Find out the volume of equalization tank to get a constant out flow for the hourly flow rate variations as given in table below: 07
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| Time | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| Flow m3/s | 0.0875 | 0.0725 | 0.0514 | 0.0434 | 0.0318 | 0.0382 | 0.0353 | 0.063 | 0.111 | 0.1315 | 0.135 | 0.135 |
| Time | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| Flow m3/s | 0.1351 | 0.129 | 0.123 | 0.1131 | 0.103 | 0.1034 | 0.1045 | 0.1156 | 0.127 | 0.128 | 0.128 | 0.118 |
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