Anna University Previous papers – Civil Engineering – Environmental Engineering – II – VI Semesters



Sixth Semester

Civil Engineering



(Model Question Paper)

Time : Four hours                                                                                     Maximum : 100 Marks


Answer ALL questions

Part – A (10 x 2 = 20 marks)


1.         State the purpose of aeration process.

2.         What do you mean by “Terminal velocity gradient (G)”?

3.         Define microstraining.

4.         State the method of disposal of screenings.

5.         What is sutro weir?

6.         How do you distinguish between plug flow and completely mixed flow?

7.         What do you mean by epilimnion zone in lakes?

8.         State the difference between sewage forming and effluent irrigation.

9.         State the causes for bulking of sludge in activated sludge process.

10.        What do you mean by two stage digestion of sludge?


Part – B (5 x 16 = 80 Marks)


11. (i)  Explain the theory of filtration in water purification.

(ii)  Distinguish between slow sand rapid sand filters with reference to

  1. Rate of filtration
  2. Filter media of sand
  3. Loss of head
  4. Effective size of sand                                                                                   (16)


12.  (a) Explain the difference between grit chamber and Detritus tank and describe the

principles involved in the design of grit chamber.                                                      (16)




(b) How are the stabilization ponds classified? Explain briefly the process of stabilization in

each case.                                                                                                              (16)



13.  (a) (i) Explain the self purification of streams and indicate how sunlight helps in such

purification?                                                                                                        (10)


(ii) Write a brief note on minimum DO content in polluted stream for survival of aquatic

life.                                                                                                                     (6)


      (b)  What are different stages of sludge digestion. Explain briefly about each stage in the

process of sludge digestion.                                                                                    (16)



14. (a) (i) Design the water depth for a mixing basin having round end baffles in order to

treat 48 million litres/day of water. The tank may be divided into two identical compartments by providing a longitudinal partition wall with each half having clear width of 8m. Assume suitable detention period and flow velocity through the basin. The clear distance between the baffles may be kept as equal to the minimum permissible. Mention the number of channels in the tank and also the overall inside length of the tank.       (16)



(b)   (i) Design a sedimentation tank for a water tank works, which supplies 1.4 x 106 litre/day

to the town. The sedimentation period is 5 hours, the velocity of flow is 12 cm/min,

depth of water in the tank is 4.0 m assuming an allowance for sludge is to be made as

80 cm.                                                                                                                 (16)



15. (a)  Design an activated sludge digester for secondary treatment of 10,000 m3 /day of

municipal wastewater. After primary clarification, the BOD is 150 mg/L, and it is desired to have not more than 5 mg/L of BOD in the effluent. A completely mixed reactor is to be used, and pilot plant analysis has established the following kinetic values; y=0.5kg/kg, kd = 0.05d-1 assuming an MLSS concentration of 3000 mg/L and an up flow concentration of 10,000 mg/L from the secondary clarifier, determine:

(i)            The volume of the reactor

(ii)           The mass and volume of solids that must be waster each day and

(iii)          The recycle ratio.                                                                                        (16)



(b)  (i)  Design the dimensions, required for sludge drying bed for the sludge obtained from

the digestion tank for 40,000 population.                                                                (8)

(ii)           Design a septic tank for the following data:

No. of people                             =  100

Sewage / capital / day                =  120 litres

Desludging period                      =  1 year

Length to width ratio                  =  4:1                                                          (8)


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