In comparing COD and BOD results for the same sample, which statement is true?

In comparing COD and BOD results for the same sample, which statement is true?

• A. Lower
• B. Approximately the same
• C. Cannot determine
• D. Higher

Answer: (D)

COD will generally be higher than BOD for the same sample because they measure oxygen demand in different ways. COD uses a chemical oxidant to break down and quantify nearly all oxidizable organics (and some inorganic substances) in a short time, regardless of whether microbes can degrade them. BOD measures only what microorganisms can biologically consume during a 5-day incubation, so it reflects mainly the biodegradable portion of the organics within that timeframe. Since COD captures more compounds and isn’t limited by biodegradability or incubation time, its value is typically higher than BOD for the same sample, often by a noticeable factor. There are cases where they’re closer if the waste is highly biodegradable, but the general rule is that COD is higher.

COD will generally be higher than BOD for the same sample because they measure oxygen demand in different ways. COD uses a chemical oxidant to break down and quantify nearly all oxidizable organics (and some inorganic substances) in a short time, regardless of whether microbes can degrade them. BOD measures only what microorganisms can biologically consume during a 5-day incubation, so it reflects mainly the biodegradable portion of the organics within that timeframe. Since COD captures more compounds and isn’t limited by biodegradability or incubation time, its value is typically higher than BOD for the same sample, often by a noticeable factor. There are cases where they’re closer if the waste is highly biodegradable, but the general rule is that COD is higher.