After five days of incubation, the samples are ready to be analysed. The samples are removed from the incubator and allowed to equilibrate to room temperature. In the meantime, the analyst should calibrate the meter again with the carboy water as discussed in the DO Sample Preparation section. It may be desired to use fresh carboy water for the calibration as discussed in the Carboy Set Up page.
Once the meter is calibrated, the samples are read starting with the blanks and ending with the actual samples. The final DO of each solution is recorded and the initial and final readings will be used to calculate the BOD. The best results come about when the initial and final DO values for the blanks are similar indicating the absence of organisms and reliable equipment. The blank DO should normally be less than 0.2 mg/L.
Continue on the the Calculations section or go back to the Introduction page.