Which test is used to estimate the chemical oxygen demand?

• A. BOD
• B. TSS
• C. COD
• D. pH

Answer: (C)

Chemical Oxygen Demand is estimated with the COD test, which uses a strong chemical oxidant to oxidize the organic matter in a sample. By measuring how much oxidant is consumed, the test provides the oxygen equivalent needed to chemically oxidize that material, usually expressed as mg/L COD. This method is fast—giving results in a few hours—and it accounts for both biodegradable and non-biodegradable organics, giving a broad picture of the wastewater’s oxidizable load. In contrast, biological oxygen demand (BOD) measures oxygen used by microbes over about five days, so it only reflects biodegradable organics that microbes can convert in that time frame. The other options either measure solids (TSS) or acidity (pH), which do not estimate oxygen demand from organics.