If a lab shows a plant influent COD of 100 mg/l and a BOD of 300 mg/l, what is most likely true?

In this scenario, the influent chemical oxygen demand (COD) is significantly lower than the biochemical oxygen demand (BOD), with COD at 100 mg/l and BOD at 300 mg/l. Typically, BOD values are expected to be lower than COD values because BOD measures the amount of oxygen required by bacteria while decomposing organic matter, while COD accounts for the total oxygen demand including both biodegradable and non-biodegradable materials.

Given that the BOD value is three times higher than the COD, this suggests an inconsistency or potential error in the laboratory measurements. A normal relationship would show a BOD that could be equal to or lower than the COD, depending on the specific characteristics of the wastewater. This significant discrepancy indicates that there may have been an error in testing, recording, or reporting the results.

It is important to understand that while some extreme cases can exist in specific types of wastewater, they are not common, and this particular situation raises a red flag regarding the accuracy of the lab results. Therefore, the nature of the results being presented strongly suggests inaccuracies in the data collection or processing rather than representing typical conditions or treatment effectiveness.