GATE Civil Engineering (CE) 2019 Shift 2 Solved Paper

Question : 58 of 65

Marks: +1, -0

Raw municipal solid waste (MSW) collected from a city contains 70% decomposable material that can be converted to methane. The water content of the decomposable material is 35%. An elemental anlysis of the decomposable material yields the following mass percent.
C : H : O: N : other = 44 : 6 : 43 : 0.8 : 6.2
The methane production of the decomposable material is governed by the following stoichiometric relation

{C}_{ {a}} {H}_{ {b}} {O}_{ {c}} {N}_{ {d}}+ {nH}_{2} {O} → {mCH}_{4}+ {sCO}_{2}+ {dNH}_{3}

Given atomic weights:

{C}=12, {H}=1, {O}=16, {N}=

The mass of methane produced (in grams, round off to 1 decimal place) per

{kg}

of raw MSW will be ____________

Your Answer:

Validate

Solution:

For the MSW, the phase diagram is as follows

From the mass percent given,

12 a=44 x

b=6 x

16 c=43 x

14 d=0.8 x

Σ=100 x

100 x=w t

of decomposable waste

=0.455 {kg}

⇒ \;\; x=\;{0.455}/{100} {kg}=4.55 {g}

⇒ {a}=16.683, {b}=27.3

{c}=12.228, {d}=0.26

From the balance of reaction we have

a=m+s . . .(A)

b+2 n=4 m+3 d . . .(B)

c+n=2 s . . .(C)

⇒ 2 c+2 n=4 s . . .(D)

⇒ b-2 c=4 m-4 s+3 d

⇒ \;\; \;{b-2 c-3 d}/{4}=m-s

⇒ {m}- {s}=0.516

⇒ {m}+ {s}=16.683

⇒ {m}=8.6

\Rightarrow

Methane produced

=8.6 × 16 {g}=137.6 {g}

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