Reuse of filter backwash water from groundwater treatment to secure drinking water supply



BMBF (Funding code 02WV1565A)
Duration: 01.02.2021 – 31.01.2024
Project partner:

Project coordination:    DVGW-Forschungsstelle TUHH

Project partner:  

  • Hamburger Wasserwerke GmbH
  • Oldenburgisch-Ostfriesischer Wasserverband
  • CERAFILTEC Germany GmbH Blue Filtration
  • Umweltbundesamt
  • PHL Substratkontor GmbH & Co. KG

Project management / project work:

Dr.-Ing. Barbara WendlerCharlotte Kast


Filter backwash water accrues during water treatment with currently between 1% and 4% of the elevated groundwater. This sludge-containing filter backwash water is usually disposed of as wastewater and is thus lost to the drinking water supply. At the same time, the demand for drinking water is continuously increasing as a result of climate, demographic and structural change. In addition, the iron and manganese-containing filter sludge is often not further recovered.

Appropriate treatment of filter backwash water could on the one hand increase the availability of drinking water for the water supply. On the other hand, the accruing iron and manganese sludge could be further processed for commercial exploitation, e.g., to bind sulphur in biogas plants, but also in agriculture and forestry, the construction industry, and environmental technologies.


In the joint project FITWAS, innovative solutions for the recovery of filter backwash water and the recycling of filter sludge are being investigated with the following objectives:

  • Clarification of the suitable process variant (pressure/vacuum filtration, direction of filtration) and membrane modules/materials (ceramic/polymer) for the treatment of filter backwash water and comparison with conventional treatment
  • Evaluation of the achievable filtration performance and the derivation of cleaning strategies with minimized use of chemicals and energy requirements
  • Legal requirements and determination of the filtrate quality for safe return to the raw water flow to be treated
  • Validation of the potential residue utilization depending on the yield and solids content as well as procedural adjustments for the storage of the filter backwash water and treatment of the filter sludge

The DVGW Research Centre TUHH, CERAFILTEC and the UBA will carry out comparative laboratory tests with ceramic and polymer membranes for efficient and reliable recovery of filter backwash water. Subsequent practical trials at selected waterworks from OOWV and HWW serve for implementation in the overall process as well as to generate reliable data on energy and operating costs. At the waterworks of UBA’s test side, the retention of viruses and heavy metals as well as their retention or resuspension are being investigated in particular. The quality and the technical or economic recycling options of the filter sludge are evaluated by PHL. This is intended to create a holistic approach to the reuse of filter backwash water from drinking water treatment, taking into account the legal framework.

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