„Install it, turn it on, it works. A fine thing with impressive effect and operational stability.“ – Horst Junge, former head of the wastewater treatment plant Cologne-Weiden, prototype hydrograv adapt, in operation since 2007.

hydrograv adapt ensures a working flocculation filtration already in the secondary clarification at any load. And with manageable technical effort, with slight energy requirement and low-maintenance. In addition, so the capacity of the secondary settling tanks is increased.

Sludge overflow and flock output – for all the progress of the wastewater technology, this is still a major problem in many wastewater treatment plants. Yet this leads to

  • unnecessary environmental pollution,
  • high wastewater charges and
  • exceedance of the discharge limits.

It is known that secondary settling tanks have very good discharge values ​​when the sludge is introduced into the tank below the sludge level. Then the flock filter works – and that is as effective as the expensive and energy-intensive downstream technical filters. hydrograv adapt exploits this flock filter always consistently with its height-variability.

In September 2007, the first hydrograv adapt inlet structure was put into operation in a secondary settling tank at the wastewater treatment plant Cologne-Weiden. The second secondary settling tank of this wastewater treatment plant is equipped with a conventional fixed inlet structure. A comparison of the operating results of both tanks is advisable.

A tank equipped with hydrograv adapt consistently shows better results:

  • significantly lower sludge level, especially in rainy weather; i.e. higher security against sludge overflow or a higher hydraulic capacity as well,
  • smaller filterable substances and considerably less visible fine flocks in the discharge,
  • greater visibility depth (i.e. clear water),
  • significantly lower floating sludge formation.

Picture: Comparison of sludge level positions in the two secondary settling tanks of the WWTP Cologne-Weiden, on the left a dry weather period, on the right a rain period. Difference of the sludge blanket layers are up to 80 cm.


Picture: qSV charges of 230 % of the permitted limit according to DWA-A 131 could be treated reliably in the hydrograv adapt tank. qA = 2 m/h.

Higher reliable secondary settling tanks enable lower combined sewer overflows in the catchment area, and even that is active water protection, because:

  • Connecting new catchment areas without the need to build a new secondary settling tank.
  • Relieve less wastewater uncleaned – more mixed water through the wastewater plant.
  • Forgo a bypass around the activation – or activate it only at much higher loads.
  • Using released secondary settling tanks for other process steps such as the trace substance elimination.
    Picture: Comparison of filterable substance values in the discharge of the two secondary settling tanks of the wastewater treatment plant Cologne-Weiden. Continuously lower filterable substance values of hydrograv adapt tanks on average and in the tips.