What is the primary difference between BOD and COD?

What is the primary difference between BOD and COD?

• A. BOD measures biological oxidation of organics under controlled conditions; COD measures total oxidizable organics, including non-biodegradable.
• B. BOD measures biological oxidation of organics under uncontrolled conditions; COD measures only biodegradable organics.
• C. BOD measures chemical oxidation of organics; COD measures biological oxidation.
• D. BOD and COD measure identical aspects of organic content.

Answer: (B)

BOD and COD measure different oxygen demands from organic matter. BOD, or Biological Oxygen Demand, gauges how much oxygen microorganisms will consume to biologically oxidize biodegradable organics under controlled lab conditions (usually at 20°C) over a set period, commonly five days (BOD5). This reflects the portion of organics that are readily biodegradable and relevant to a biological treatment process. COD, or Chemical Oxygen Demand, uses a strong chemical oxidant to oxidize organic matter in a sample under acidic conditions. It measures the total amount of oxygen needed to oxidize both biodegradable and non-biodegradable organics, and it is typically completed in a matter of hours. Because it includes substances that microbes can’t readily degrade, COD values are generally higher than BOD values. So the main difference is that BOD captures the biodegradable, biologically oxidizable portion under controlled conditions over time, while COD captures the total oxidizable organic load with a fast chemical method.

BOD and COD measure different oxygen demands from organic matter. BOD, or Biological Oxygen Demand, gauges how much oxygen microorganisms will consume to biologically oxidize biodegradable organics under controlled lab conditions (usually at 20°C) over a set period, commonly five days (BOD5). This reflects the portion of organics that are readily biodegradable and relevant to a biological treatment process.

COD, or Chemical Oxygen Demand, uses a strong chemical oxidant to oxidize organic matter in a sample under acidic conditions. It measures the total amount of oxygen needed to oxidize both biodegradable and non-biodegradable organics, and it is typically completed in a matter of hours. Because it includes substances that microbes can’t readily degrade, COD values are generally higher than BOD values.

So the main difference is that BOD captures the biodegradable, biologically oxidizable portion under controlled conditions over time, while COD captures the total oxidizable organic load with a fast chemical method.