Which statement about BOD5 is true?

Which statement about BOD5 is true?

• A. BOD5 is measured by assessing color changes in the sample.
• B. BOD5 represents the biochemical oxygen demand over five days and is used as a standardized measure of readily biodegradable organic matter.
• C. BOD5 measures inorganic oxygen demand.
• D. BOD5 is unaffected by temperature.

Answer: (B)

Biochemical oxygen demand over five days gauges how much oxygen microorganisms need to biologically oxidize the organic material in a sample, recorded during a five-day period. This provides a standardized measure of readily biodegradable organic matter because it reflects the portion of pollution that microbes can break down quickly. In practice, a diluted wastewater sample is incubated with a microbial seed at a controlled temperature (traditionally 20°C) in the dark, and the drop in dissolved oxygen from the start to after five days is the BOD5. It is not based on color changes, and it does not measure inorganic oxygen demand. Temperature matters because microbial activity—and thus the rate of oxygen consumption—depends on temperature, which is why the test uses a standard temperature for comparability.

Biochemical oxygen demand over five days gauges how much oxygen microorganisms need to biologically oxidize the organic material in a sample, recorded during a five-day period. This provides a standardized measure of readily biodegradable organic matter because it reflects the portion of pollution that microbes can break down quickly. In practice, a diluted wastewater sample is incubated with a microbial seed at a controlled temperature (traditionally 20°C) in the dark, and the drop in dissolved oxygen from the start to after five days is the BOD5. It is not based on color changes, and it does not measure inorganic oxygen demand. Temperature matters because microbial activity—and thus the rate of oxygen consumption—depends on temperature, which is why the test uses a standard temperature for comparability.