A waste activated sludge (WAS) is to be blended with green waste (GW). The carbon (C) and nitrogen (N) contents, per {kg} of WAS and GW on dry basis are given in the table. Parameter WAS GW Carbon (g) 54 360 Nitrogen 10 6 The ratio of WAS to GW required (up to two decimal places) to achieved a blended C:N ratio of 20: 1 on dry basis is

GATE Civil Engineering (CE) 2018 Shift 1 Solved Paper

Question : 36 of 65

Marks: +1, -0

A waste activated sludge (WAS) is to be blended with green waste (GW). The carbon (C) and nitrogen (N) contents, per

{kg}

of WAS and GW on dry basis are given in the table.

The ratio of WAS to GW required (up to two decimal places) to achieved a blended C:N ratio of

20: 1

on dry basis is

Solution:

Let

20 {kg}

xof

{C}

and

1 {kg}

{N}

is required
Let

× {kg}

of WAS is taken

∴ \;\;

Carbon in

× {kg}=0.054 × {kg}

Nitrogen in

× {kg}=0.010 × {kg}

Let y

{kg}

{GW}

is taken

∴ \;\;

Carbon in

× {kg}=0.360

{kg}

Nitrogen in

× {kg}=0.006 × {kg}

Total Carbon,

0.054 x+0.36 y=20 {kg}

Total Nitrogen,

0.01 x+0.0 \;\; 06 \;\; y=1 {kg}

x=73.26

y=44.566

∴ \;\; \;{x}/{y}=\;{W A S}/{G W}=1.6438 ≃

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