What is Chemical Oxygen Demand (COD)?

Chemical Oxygen Demand (COD) is a critical water quality parameter used to measure the amount of organic compounds in water. Specifically, it represents the quantity of oxygen required to chemically oxidize the organic matter present in a water sample using a strong oxidizing agent, typically potassium dichromate in an acidic medium. Unlike Biological Oxygen Demand (BOD), which measures oxygen used by microorganisms over a 5-day period, COD provides a faster assessment of water pollution levels, making it the preferred metric for industrial wastewater monitoring.

How to Use the COD Calculator

To calculate the Chemical Oxygen Demand using the open reflux or closed reflux titration method, you need specific data from your laboratory experiment. This tool uses the standard formula:

COD (mg/L) = [(A - B) × N × 8000] / Volume of Sample

• A: The volume of Ferrous Ammonium Sulfate (FAS) used for the blank titration.
• B: The volume of FAS used for the actual sample titration.
• N: The exact normality of the FAS solution used.
• 8000: The milliequivalent weight of oxygen multiplied by 1000 to convert to mg/L.

Why is COD Important in Wastewater Treatment?

High COD levels indicate a high concentration of oxidizable organic matter, which can lead to oxygen depletion in receiving water bodies. This depletion is harmful to aquatic life. In industrial settings, COD testing is essential for ensuring compliance with environmental regulations. It allows plant operators to adjust treatment processes in real-time, as the results are typically available within 2-3 hours, compared to the 5 days required for BOD testing.

Frequently Asked Questions (FAQs)

Q: What is the difference between COD and BOD?
A: COD measures all chemically oxidizable matter, whereas BOD only measures the portion that can be biologically oxidized by bacteria. COD values are almost always higher than BOD values for the same sample.

Q: What are typical COD levels?
A: Clean river water usually has a COD below 20 mg/L, while untreated domestic sewage may range from 200 to 600 mg/L. Industrial wastewater can reach tens of thousands of mg/L.