The GATE Grind

GATE 2018 CE (CE1) – Question 63

Air Pollution and Municipal Solid Wastes · Municipal solid wastes: generation, collection, transportation and management · 2 marks · Numerical answer

On a dry basis, each kg of waste activated sludge (WAS) contains 54 g carbon and 10 g nitrogen; green waste (GW) contains 360 g carbon and 6 g nitrogen. Required WAS/GW dry-mass ratio for blended C:N = 20:1, to two decimals, is ______.

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Correct answer: 1.60 to 1.70

Explanation

Let r kg WAS be blended with 1 kg GW. Set $(54r+360)/(10r+6)=20$. Thus $146r=240$ and WAS/GW = 1.64 by dry mass.