Wastewater Strength — What does the Chemical Oxygen Demand (COD) parameter measure for a water/wastewater sample?

Introduction:
Chemical Oxygen Demand (COD) is a widely used aggregate measure of wastewater strength. It estimates the oxygen equivalent of organics (and some oxidizable inorganics) by chemical oxidation, typically using a strong oxidant under acidic conditions. This metric helps design treatment processes and monitor compliance.

Given Data / Assumptions:

• Standard dichromate COD test under reflux, acidic conditions, with catalysts.
• COD reported in mg O2/L.
• Sample may contain biodegradable and non-biodegradable organics.

Concept / Approach:

COD represents the oxygen that would be consumed if the oxidizable materials in the sample were fully oxidized. Unlike BOD (Biochemical Oxygen Demand), which measures oxygen uptake by microorganisms over time, COD is a faster chemical test and often yields higher values because it oxidizes a broader spectrum of compounds.

Step-by-Step Solution:

Verification / Alternative check:

Comparisons of COD and BOD in plant data show COD ≥ BOD in most cases; the ratio guides biodegradability assessments and process selection.

Why Other Options Are Wrong:

A confuses COD with BOD related to microbial growth. C focuses on calcium oxidation, which is not the essence of COD. D and E do not describe COD at all.

Common Pitfalls:

Equating COD directly with BOD; always interpret together for biodegradability insights. Ensure chloride interference is addressed during testing.

Final Answer:

The amount of oxygen that would be consumed to chemically oxidize pollutants (primarily organic matter) present in the sample