Reuse of backwash water at waterworks

At the waterworks in the Danish city of Farum they treat approximately 500,000 cubic meters of water each year through open sand filters. Periodically, production must be interrupted to backwash the filters. This backwashing is essential to remove iron precipitation from the filters, extend the life of the filter material and achieve satisfactory water treatment overall. The filter rinse water is collected in the trap tank, but instead of being discharged as wastewater, Farum Waterworks has chosen a solution where the rinse water is reused and becomes clean drinking water again.

The solution for re-filtration consists primarily of two EUROWATER pressure filters, set up as pre- and after-filter with a treatment capacity of 8 m³/h. As the water has been standing still in the trap tank, additional safety against bacteriological contamination is required. This is achieved with a UV disinfection system type Spektron 30e from Wedeco. The quality of the treated rinse water is monitored by a turbidity meter before it is fed into the raw water, passes through the open sand filters and becomes clean drinking water again.

As much as 96% of the filter rinse water is reused at Farum Waterworks. A volume of water equivalent to the average drinking water consumption of 100 households in Denmark. Calculated on the basis of the current diversion cost per cubic meter, this represents an annual saving of almost 67,000 euro - every year!