5 January 2016

GATE Question.

GATE 2014

At a site, based on percolation test, the allowable rate of treated sewage application was determined as 65 L/m2/day. The effective depth (m) of a soak pit with a diameter of 2.5 m for the disposal of 1020 L/day of septic tank effluent is ______________

Answer: 1.98 to 2.02

Soln:
Let the depth of cylindrical pit be ‘h’ and radius = 1.25 m (given)
Total surface area for absorption= πr2 + 2πrh
                                                     = πr (r + 2h)
               Total absorbed effluent= πr (r + 2h) ×1020
                                                     = 3.14× 1.25(1.25 + 2h) = 1020     


Solving it, h= 2m  

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