# Civil Engineering - Waste Water Engineering - Discussion

### Discussion :: Waste Water Engineering - Section 1 (Q.No.6)

6.

If the diameter of sewer is 225 mm, the gradient required for generating self cleansing velocity, is

 [A]. 1 in 60 [B]. 1 in 100 [C]. 1 in 120 [D]. none of these.

Explanation:

No answer description available for this question.

 Sandip Ghosh said: (Dec 9, 2014) But actually 1 in 105 for a velocity of 0.9m/s & 1 in 150 for a velocity of 0.75m/s.

 Aman Gautam said: (Dec 10, 2014) @Sandeep. Greater is the gradient, greater is the velocity. Thus your point is wrong and as for 225 mm diameter, velocity should be 1 m/s. So it would require the highest gradient.

 Manohar said: (Jul 9, 2015) Yes, the gradient, 1 in 105 is greater than 1 in 150.

 Ganesh said: (Oct 29, 2015) Which formula is used here to calculate self cleansing formula?

 Akash said: (Dec 26, 2015) V-under root (8 beta under f multiply by (specific gravity of solids- 1)*g*diameter of solids). Find v and using manning or any other formula find slope. But data is not sufficient.

 Narayan said: (Jan 17, 2016) Velocity of the sewer is 0.9 to 0.75 m^3/s. So assume velocity of sewer V = 0.9 m/s. And using the manning's formula: V = R^2/3*s^1/2/n but the wastage flow is not specify.

 Ritesh Dev Singh said: (Dec 20, 2016) By Shield's Theory, Self - cleansing velocity (Vs), Vs= √ {8kgd'(G-1)}÷f], where, k= (1-n)sin θ.

 Vaibhav Gupta said: (May 9, 2017) Explain the expression for self-cleaning velocity.

 Himajwala said: (Aug 21, 2017) I didn't understand which formula was used. Can anyone help me?

 Sanjay said: (Sep 9, 2017) Self cleaning velocity is 0.75 m/s to 0.9 m/s. So 100/120 =0.83. 100/60 =1.66. 100/100 =1. So right answer is 1 in 120.

 Dheeraj Singh said: (Sep 16, 2017) The slope of sewer should be designed for min permissible velocity at min flow but in this case, a material made of sewer not given so can't be calculated if I assume brick-lined sewer then calculate slope by given velocity trial and error velocity (1to2.5).

 Gubendhiran said: (Jan 13, 2018) Using Manning's formula. Vs=[(R^0.67)*(S^0.5)]/n. For circular sewer R=D/4=0.225/4=0.05625m. Vs=ranges from 0.45 to 0.8 m/s from S.K.GARG EEN Vol IIT. Take Max for design Vs=0.8 m/s. n=Manning's constant=0.015. 0.8=[(0.05625^0.67)*(S^0.5)]/0.015. (S^0.5)=0.08253. S=0.00681. S=1/147. So we can option 'C'.