The Biological Oxygen Demand (BOD5) is an indirect measurement of carbon compounds by direct measuring the amount of oxygen consumed by the microorganism at a temperature of 20°C within 5 days. Knowing the difference of BOD5 levels from inlet and effluence of the wastewater plant makes calculation of the cleaning efficiency easy. Common values of BOD5 are: 400-1000 mg/l at the inlet of the treatment plant and below 50 mg/l at the effluence of the plant.
2 different methods for BOD determination are commonly used.
The direct measurement of DO-content of sample and different dilutions every day with a DO-probe and calculating the BOD5 at the end. This method may also be performed with the above mentioned meter Multiline P3 using some accessories. The more convenient method for municipal waste water is a respirometric measurement with an OxiTop Measuring and storing the data every 24 hours automatically the samples have not to be touched between filling the bottle and reading data after 5 days.