What is one of the requirements for a BOD test?

To conduct a Biochemical Oxygen Demand (BOD) test accurately, it is essential that the BOD bottle is completely filled to the top. This is crucial because a full bottle minimizes the amount of air trapped in the water sample, reducing the potential for oxygen that could support bacterial growth outside the intended anaerobic condition of the test. If there is air in the bottle, it could lead to higher initial measurements of dissolved oxygen, which would make the results unreliable and underestimate the actual BOD levels.

The BOD test is designed to measure the amount of oxygen consumed by microorganisms in a sample over a specified period, typically five days. Therefore, ensuring that the sample is free from air contact is critical for obtaining valid results. In contrast, options suggesting only partial filling, conducting the test at room temperature, or collecting a minimum number of samples do not directly address the critical aspects of sample integrity required for accurate BOD measurements.