Which process occurs without oxygen, producing acid and odorous gases?

• A. Shock Load
• B. BOD Test
• C. Hydrogen Sulfide
• D. Anaerobic Decomposition

Answer: (D)

In environments without oxygen, microorganisms break down organic matter through anaerobic decomposition. Without oxygen, the microbes use pathways that yield organic acids and odorous gases as byproducts. Depending on conditions, this can include hydrogen sulfide, methane, and other foul compounds, which is why the process is associated with strong odors and acid formation. This contrasts with aerobic processes that require oxygen and tend to produce fewer odors because they break down matter more completely.

The other terms describe something different: a shock load is a sudden surge in contaminant or load, a BOD test measures how much oxygen is needed to decompose a sample, and hydrogen sulfide is a gas produced under anaerobic conditions rather than the overall process itself.