Influence of temperature on the performance of variable declining rate filters for drinking water

A water treatment plant from the Rudawa river was tested in order to investigate temperature influence on the hydraulics of variable declining rate (VDR) filters. For this filter plant supplied with raw surface water the effect of temperature on head loss in filter media was well documented, but the effect on the turbulent flow through a designed system of orifices proved to be limited. It was found that for the particular plant investigated, peak demands can occur in winter when the water is cold. Concluding, the VDR filters need to be designed for winter conditions but proper operation requires nomograms for the water table fluctuations over the filters as a function of the water demands and temperature. For the bank of data collected from the tested filter plant the operation based on the same maximum flow through a clean filter led to acceptable fluctuations of the water table. (from Authors)