DWA Guideline M 209 describes the execution and evaluation of oxygen transfer measurements for aeration equipment in activated sludge systems, both under clean-water conditions and under operating conditions with activated sludge. It complements DIN EN 12255-15 for clean-water testing and covers absorption tests, desorption tests, and off-gas measurements, including terminology, measured variables, chemicals, test equipment, evaluation methods, and reporting requirements.
For oxygen transfer testing, the guideline recommends a clearly defined test procedure with predetermined boundary conditions. This includes documentation of tank geometry, the use of suitable and calibrated measuring instruments, and measurement of dissolved oxygen, temperature, air flow rate, and power consumption. It also addresses the proper selection and dosing of chemicals such as sodium sulfite, cobalt catalyst, nitrogen, and pure oxygen.
Equally important are transparent data evaluation procedures, comprehensive reporting, and—particularly in tender specifications—clear agreements regarding the testing methodology, since a simple reference to DWA-M 209 alone is not sufficient.
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