Question

Which of the following process of safe disposal of waste will require least amount of energy input?

• A. Incineration
• B. Pyrolysis
• C. Composting
• D. Plasma Arc

Hint:

Energy input hierarchy in waste processing:
Plasma Arc ($> 3000^\circ\text{C}$) $\gg$ Incineration/Pyrolysis ($400-1100^\circ\text{C}$) $\gg$ Composting (ambient biological process).
Biological processes use natural microbial metabolism and consume the least external energy.

Answer 1

The Correct Option is C

Concept:
Solid waste management uses both thermal and biological technologies to treat municipal solid waste.
Thermal processes require substantial auxiliary energy inputs to sustain elevated temperatures, whereas biological methods rely on natural microbial metabolic processes.

Step 1: Energy Inputs of Thermal Waste Technologies:
1. Plasma Arc Gasification (D): Directs waste into an insulated vessel where an electric plasma torch generates temperatures exceeding $3000^\circ\text{C}$ to $10000^\circ\text{C}$. This requires massive external electrical energy to break chemical bonds into vitrified slag and syngas.
2. Incineration (A): Controlled combustion of solid waste at $850^\circ\text{C}$ to $1100^\circ\text{C}$. It requires auxiliary fuels (diesel or natural gas) to maintain furnace temperatures, alongside forced-draft air blowers and emission scrubbers.
3. Pyrolysis (B): Endothermic thermal degradation of carbonaceous waste in an oxygen-free atmosphere at $400^\circ\text{C}$ to $800^\circ\text{C}$, demanding sustained external heat input to convert waste into bio-oil, syngas, and biochar.

Step 2: Energy Inputs of Biological Treatment:
Composting (C): A natural biological decomposition of organic solid wastes carried out by indigenous aerobic or anaerobic micro-organisms (bacteria, actinomycetes, and fungi).
The process is biologically driven and self-heating due to microbial metabolism. External energy input is minimal, limited to occasional physical turning or passive aeration in windrow piles.
Final Answer:
Composting relies on natural biological breakdown and requires the least amount of energy input, corresponding to option (C).