Wastewater New York State Practice Exam

What is the minimal residual dissolved oxygen content for a BOD5 test?

1. 0.5 mg/L

2. 1.0 mg/L

3. 1.5 mg/L

4. 2.0 mg/L

The correct answer is: 1.0 mg/L

The minimal residual dissolved oxygen content required for a BOD5 (Biochemical Oxygen Demand over 5 days) test is 1.0 mg/L. This is critical because the BOD5 test is designed to measure the amount of oxygen that is consumed by microorganisms during the degradation of organic matter in a water sample over a specified five-day period. Maintaining a dissolved oxygen level of at least 1.0 mg/L ensures there is enough oxygen available for the microorganisms to perform their metabolic activities effectively. If the dissolved oxygen concentration falls below this level, it could lead to inaccuracies in determining the actual BOD of the sample, as the microorganisms may not receive sufficient oxygen for complete respiration, thereby yielding an artificially low result. In the context of the other options, values below this threshold would compromise the validity of the test, as they do not provide adequate conditions for aerobic biological activity. Thus, 1.0 mg/L is established as the minimum requirement to ensure proper conditions for the test's reliability and accuracy.