Estimate of BOD5 by means of oxygen uptake rate (OUR) respirometric tests on urban wastewater

Biochemical oxygen demand (BOD5) is a key indicator of organic pollution in wastewater, but its conventional determination requires at least 5 days, limiting its use for real-time monitoring and process control. This study proposes a rapid alternative method based on measuring the oxygen uptake rate (OUR) to estimate BOD5. Approximately 100 tests were conducted to correlate BOD5 with the Delta OURs value, defined as the difference between exogenous and endogenous respiration. Samples were collected from 13 urban wastewater treatment plants (WWTPs) of different capacities, evaluating both raw influent and wastewater after pretreatment. For these conditions, the model estimated BOD5 as 11.172 times the Delta OURs. The accuracy of the correlation was also assessed, considering the percentage of industrial wastewater contribution. A stronger correlation was observed in WWTPs with an industrial load between 10 and 30%, where BOD5 was estimated as 10.544 times the Delta OURs. Overall, the results demonstrate that OUR measurement can serve as a reliable and fast alternative to standard BOD5 analysis, enabling real-time estimation of organic pollution in wastewater and helping overcome the limitations of conventional analytical methods.