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Geophysics in sand filters

3D mapping of ochre in sand filters (3D-FIL)

In Denmark as in several other countries, drinking water originates from groundwater treated in open sand filters. For optimal performance, the open sand filters must be backwashed periodically to prevent clogging. However, the waterworks often have insufficient knowledge about the performance of the backwash processes. In this project, a geophysical method based on DC/IP principles was developed for continuous geoelectrical measurements on the upper 30 cm of the open filter where the clogging occurs, mainly due to iron oxidation. Based on the geophysical measurements it is possible to optimise the backwash process with respect to frequency and duration, and thus increase the lifetime of the filters, save water and energy at the waterworks, and ensure higher drinking water quality.

The collaboration partners were VIA University College Horsens, Niras and Lemvig Vand og Spildevand, who provided access to one of their active filters.



  • ERT/IP
  • ABEM Terrameter LS
  • Remote control unit
  • Custom electrodes
  • Lemvig Vand og Spildevand
  • VIA University College Horsens
  • Niras
  • HGG, Department of Geoscience, Aarhus University