Summary:

The article presents common used methods for measuring dissolved oxygen concentration at wastewater facilities. The described methods include Winkler titration and instrumental measurements, such as electrochemical sensors and more recent developed optical ones. The principles, analysis procedures as well as advantages and drawbacks of the methods were discussed. Furthermore, the valid ISO and PN-EN standards for dissolved oxygen measurements were shortly presented with emphasis on the recent changes concerning standards for the optical sensor method. As the results of a survey conducted among wastewater treatment plant operators in southern Poland reveal, optical sensors are being currently preferred in on-line applications due to their enhanced properties in comparison to other measurements methods.