Aeration tanks - first biological cleaning stage

Inside the aeration tanks, the wastewater is subjected to biological cleaning. A myriad of microorganisms (bacteria, protozoa etc.), which are referred to as “activated sludge”, rid the wastewater of carbon, nitrogen and phosphorus compounds. The process that takes place inside the aeration tanks is the same as in natural waters - but more efficient, more concentrated and quicker.

Impurities in the primary clarifier outflow serve as a nutrient source for these microorganisms. They absorb them into their cells and break them down step by step. In other words, they remove them by respiration. To perform these cleaning processes, microorganisms need a lot of oxygen. This oxygen is blown into the first biological cleaning stage by means of centrifugal aerators. These aerators immerse in the wastewater-sludge mixture and create a turbulent motion, thereby blowing in enormous amounts of air. Return sludge from the intermediate sedimentation stage is also fed into the aeration tanks to assure a constant and sufficient supply of microbial mass. In the wake of these degradation processes, the amount of microbial mass steadily increases. The resulting excess sludge – approx. 100 tonnes per day - is continuously withdrawn.

The first biological cleaning stage primarily serves to remove carbon (approx. 80%) and to a lesser extent also nitrogen (35%). Nitrogen is mostly removed in the second stage (nitrification and denitrification). A precipitant is added to convert the dissolved phosphorus into insoluble compounds, which are then eliminated along with the excess sludge.

Technical parameters

  • 4 tanks (cascade 1-3)
  • Length: 73,5 m
  • Tank width: 19 m each
  • Depth: 6.8 m
  • 4 tanks (cascade 4)
  • Length: 68,4 m
  • Tank width: 7,05 m
  • Depth: 6.8 m
  • Total volume: 51,000 m³

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Next step:
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