Sewage stabilization – Definition of relative stability: The ratio of oxygen available to the oxygen required for stabilization of sewage is known as what?

Introduction / Context:
Sewage stabilization reflects the degree to which biodegradable organics have been oxidized. Classical sanitary engineering introduced the concept of relative stability to quickly assess whether the oxygen present (or supplied) is sufficient to meet the biochemical demand.

Given Data / Assumptions:

• Aerobic stabilization is considered.
• Oxygen available and oxygen required are compared as a ratio.

Concept / Approach:
Relative stability = oxygen available / oxygen required. If this value approaches 1 (or 100%), the sewage is considered stable, meaning minimal further oxygen demand remains. This is a different concept from BOD, which measures oxygen required; relative stability compares requirement to availability.

Step-by-Step Solution:
Identify that the ratio (available/required) is being asked.Recall the term used historically in wastewater texts: relative stability.

Verification / Alternative check:
Old-standard assays (e.g., 5-day BOD alongside relative stability tests) collectively indicate oxygen balance in receiving waters.

Why Other Options Are Wrong:

• BOD/COD: measure oxygen demand of organics; not a ratio to available oxygen.
• Bacterial stability factor/oxygen ion concentration: non-standard or incorrect terminology.

Common Pitfalls:
Conflating BOD (demand) with stability (balance of supply versus demand).

Final Answer:
Relative stability