GATE 2023 CE (CE1) – Question 62
The composition and energy content of a representative solid waste sample are given in the table. If the moisture content of the waste is 26%, the energy content of the solid waste on dry-weight basis is _____ MJ/kg (round off to one decimal place).
| Component | Percent by mass | Energy content as-discarded basis (MJ/kg) |
|---|---|---|
| Food waste | 20 | 4.5 |
| Paper | 45 | 16.0 |
| Cardboard | 5 | 14.0 |
| Plastics | 10 | 32.0 |
| Others | 20 | 8.0 |
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Correct answer: 18.31 to 18.49
Explanation
The mass-weighted energy content on the as-discarded basis is $0.20 \times 4.5 + 0.45 \times 16 + 0.05 \times 14 + 0.10 \times 32 + 0.20 \times 8 = 0.9 + 7.2 + 0.7 + 3.2 + 1.6 = 13.6$ MJ/kg. The waste is 26% water, so the dry mass is 74% of it, and per kg of dry waste the energy is $\frac{13.6}{0.74} = 18.4$ MJ/kg.