Which measure is defined as the amount of oxygen needed by microorganisms to decompose organic matter?

• A. Shock Load
• B. BOD
• C. Infiltration/Inflow
• D. Anaerobic Decomposition

Answer: (B)

The idea being tested is how we quantify the oxygen that microorganisms need to break down organic matter. This measure is Biological Oxygen Demand, or BOD. It indicates the strength of organic pollution: more organic material requires more oxygen for microbes to decompose it, so a higher BOD means greater potential for oxygen depletion in water. That’s why BOD is widely used in wastewater treatment and water-quality assessments—to gauge how much oxygen will be consumed as organics are broken down and to help design processes that protect aquatic life.

Why this measure fits best: it directly captures the amount of oxygen that microorganisms will use to decompose organic matter, which is exactly what BOD measures.

Why the other terms don’t fit as this measure: a shock load refers to a sudden spike in pollutant input, not a standard oxygen-demand metric; infiltration/inflow describes extra water entering a sewer system, affecting volume rather than the oxygen demand of organics; anaerobic decomposition is the breakdown of material without oxygen, which is the opposite of what BOD gauges (the oxygen used by microbes to decompose organics under typical conditions).