DIN EN 12255 is a series of European standards for the design and construction of wastewater treatment plants. Part 15 of this standard addresses aeration systems in activated sludge processes. It defines fundamental requirements for equipment sizing, material selection, and operational reliability. The objective is to ensure a uniform oxygen supply to the activated sludge while considering both energy efficiency and operational safety.
The standard requires that the design be based on the maximum oxygen demand of the biological treatment stage. Factors such as temperature, salinity, altitude, and oxygen transfer efficiency (OTE) must be taken into account. Oxygen input calculations are based on the Standard Oxygen Transfer Rate (SOTR), which is adjusted using correction factors for wastewater conditions (α-factor and β-factor). The standard provides guideline values for the required dissolved oxygen concentration in activated sludge tanks and requires an even distribution of diffusers to prevent dead zones.
Part 15 further establishes a standardized performance testing procedure for aeration equipment in clean water. It specifies requirements for measurement methods, measured parameters, and evaluation procedures for oxygen transfer and oxygen yield, enabling objective comparison of aeration systems. However, the clean-water test is only partially transferable to actual wastewater conditions and assumes either completely mixed tanks or a uniform diffuser distribution.
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