Reduced water loss at Farum Waterworks

Each year Farum Waterworks treats a water volume of approximately 500,000 cubic metres over open sand filters. At regular intervals, the water production must be interrupted to backwash the filters. This backwash is essential to remove iron precipitations from the filters, extend the life of the filter media, and to achieve a satisfactory water treatment altogether. The filter rinsing water is collected in the precipitation tank, but instead of being discharged as wastewater, Farum Waterworks has chosen a solution in which the rinsing water is reused and becomes clean drinking water again.

The solution for re-filtration primarily consists of two SILHORKO pressure filters type TFB 25, arranged as prefilter and secondary filter with a treatment capacity of 8 m³/h. Since the water has been stagnant in the precipitation tank, extra safety against bacteriological contamination is required. This is obtained using a UV disinfection system type Spektron 30e from Wedeco. The quality of the treated rinsing water is monitored by a turbidity meter before it is conducted into the raw water, runs through the open sand filters and again becomes clean drinking water.

As much as 96% of the filter rinsing water is reused at Farum Waterworks. A water volume corresponding to the average drinking water consumption of 100 households. Based on the current water discharge cost per cubic meter, this is an annual saving of almost half a million Danish kroner – every year!