The GATE Grind

GATE 2022 CE (CE2) – Question 43

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

In a city, the chemical formula of biodegradable fraction of municipal solid waste (MSW) is C100H250O80N. The waste has to be treated by forced-aeration composting process for which air requirement has to be estimated. Assume oxygen in air (by weight) = 23 %, and density of air = 1.3 kg/m3. Atomic mass: C = 12, H = 1, O = 16, N = 14. C and H are oxidized completely whereas N is converted only into NH3 during oxidation. For oxidative degradation of 1 tonne of the waste, the required theoretical volume of air (in m3/tonne) will be (round off to the nearest integer)

  1. 4749
  2. 8025
  3. 1418
  4. 1092

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) 4749

Explanation

Balance oxidation as $C_{100}H_{250}O_{80}N+121.75O_2\to100CO_2+123.5H_2O+NH_3$. Molecular mass of waste is 2744, and required oxygen mass is 121.75×32=3896 per mole.

For one tonne, oxygen requirement is $1000(3896/2744)=1419.825$ kg. Air mass is this divided by 0.23, then volume is divided by 1.3: **4748.58≈4749 m³ (A)**.