Sewage putrefaction gases: During the putrefaction (anaerobic decomposition) of sewage, which gases are typically given off?

Introduction / Context:
In the absence of oxygen, sewage undergoes putrefaction (anaerobic decomposition). Recognizing the characteristic gases evolved is important for ventilation design, odor control, worker safety, and corrosion mitigation in sewers and treatment units.

Given Data / Assumptions:

• Environment is anaerobic (limited or no free oxygen).
• Decomposition of organic matter by anaerobic bacteria.
• Typical byproducts include various reduced and oxidized gases.

Concept / Approach:
During putrefaction, organic compounds are broken down to produce a mixture of gases. Common constituents are methane (from methanogenesis), carbon dioxide (from fermentation steps), hydrogen (from certain fermenters), along with other malodorous gases such as hydrogen sulfide and traces of ammonia and volatile organics. The presence of these gases dictates the need for gas handling and monitoring systems.

Step-by-Step Solution:
Identify anaerobic pathways: fermentation and methanogenesis.Major gases: CH4 (methane), CO2 (carbon dioxide), H2 (hydrogen).Ancillary gases: H2S, NH3, and others may also be present depending on sewage composition.Since H2, CH4, and CO2 are all plausible, the inclusive option is correct.

Verification / Alternative check:
Operational data from anaerobic digesters and septic environments confirm methane and carbon dioxide as dominant gases with hydrogen and traces of other compounds also present, validating the comprehensive choice.

Why Other Options Are Wrong:
Single-gas options (Hydrogen, Methane, Carbon dioxide) omit other well-known byproducts.“Ammonia only” disregards the principal methane and carbon dioxide components in anaerobic environments.

Common Pitfalls:

• Confusing aerobic oxidation (which mainly produces CO2) with anaerobic putrefaction (which also yields CH4 and H2).
• Ignoring safety; methane is combustible and hydrogen sulfide (often present) is toxic and corrosive.

Final Answer:
All of the above