GATE 2017 CE (CE2) – Question 60

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

Municipal-solid-waste components are listed as (mass %, moisture %, energy kJ/kg as discarded): food (20,70,2500); paper (10,4,10000); cardboard (10,4,8000); plastic (10,1,14000); garden trimmings (40,60,3500); wood (5,20,14000); tin cans (5,2,100). The difference between energy content on a dry basis and as-discarded basis is ______ kJ/kg.

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Correct answer: 3850 to 3900

Explanation

For 1 kg as discarded, the weighted energy sum is 5805 kJ. The weighted water mass is $0.14+0.004+0.004+0.001+0.24+0.01+0.001=0.400$ kg, leaving 0.600 kg dry matter. Dry-basis energy is $5805/0.6=9675$ kJ/kg. Difference: $9675-5805=3870$ kJ/kg.