Question

Which of the following gas is produced from landfill wastes?

• A. Biogas
• B. Compressed Natural gas
• C. Liquified petroleum gas
• D. Both Liquified petroleum gas and Compressed Natural gas

Hint:

(c) \textbf{Landfill gas (LFG)} is produced by the anaerobic decomposition of organic waste in landfills.
(d) LFG is a type of \textbf{Biogas}.
(e) Main components: Methane (CH$_4$) and Carbon Dioxide (CO$_2$).
(f) Natural Gas (source of CNG) is primarily methane from fossil deposits. LPG is propane/butane from petroleum/natural gas processing.

Answer 1

The Correct Option is A

Landfill waste, particularly organic waste (food scraps, paper, yard trimmings, etc.), undergoes anaerobic decomposition (decomposition in the absence of oxygen) by microorganisms. This process produces a mixture of gases known as landfill gas (LFG). The primary components of landfill gas are:
(\) Methane (CH$_4$): Typically 40-60% by volume. Methane is a potent greenhouse gas but also a valuable fuel.
(]) Carbon Dioxide (CO$_2$): Typically 40-60% by volume.
(^) Trace amounts of other gases: Nitrogen (N$_2$), oxygen (O$_2$ - if air intrudes), hydrogen sulfide (H$_2$S), ammonia (NH$_3$), various volatile organic compounds (VOCs). This mixture of methane and carbon dioxide (with trace gases) produced from the anaerobic digestion of organic matter is commonly referred to as Biogas. Landfill gas is a type of biogas. Biogas can be captured from landfills and used as an energy source (e.g., to generate electricity or heat), or it can be flared to convert methane to CO$_2$ (which is a less potent greenhouse gas than CH$_4$ over shorter timeframes). Let's evaluate the options:
(_) (a) Biogas: This is the general term for gas produced from anaerobic decomposition of organic matter, and landfill gas is a prime example.
(`) (b) Compressed Natural Gas (CNG): Natural gas is primarily methane (CH$_4$) extracted from geological deposits. CNG is natural gas compressed for use as fuel. While landfill gas contains methane, it's not "natural gas" in the sense of fossil fuel origin, and it typically requires processing (upgrading) to remove CO$_2$ and impurities to reach natural gas quality if it's to be used as CNG.
(a) (c) Liquefied Petroleum Gas (LPG): LPG consists mainly of propane (C$_3$H$_8$) and butane (C$_4$H_{10}$), which are byproducts of petroleum refining and natural gas processing. It is not produced from landfill waste.
(b) (d) Both Liquified petroleum gas and Compressed Natural gas: Incorrect, as LPG is not produced, and LFG is distinct from natural gas though it contains methane. Therefore, the gas produced from landfill wastes is Biogas (specifically, landfill gas, a type of biogas). \[ \boxed{\text{Biogas}} \]