Which statement best describes Carbonaceous Biochemical Oxygen Demand (CBOD) measurement?

• A. It measures the oxygen demand exerted by all organic and inorganic substances.
• B. It measures only the nitrogenous oxygen demand.
• C. It measures only the oxygen demand exerted by carbonaceous compounds, excluding nitrogenous compounds.
• D. It measures the total oxygen demand including nitrogenous and carbonaceous demands.

Answer: (C)

CBOD measures the oxygen used to oxidize carbonaceous organic matter, while nitrification (the nitrogen-related oxygen demand) is inhibited. By blocking the nitrification step, the test removes the oxygen consumption tied to converting ammonia to nitrite/nitrate, so the result reflects only the carbon-based biodegradable oxygen demand. The other statements mix in inorganic or nitrogenous components or describe the total BOD, which CBOD is not.