DynaSand filtration for drinking-water production

DynaSand filtration is a continuous type of rapid sand filtration which can handle high loads of suspended solids and has therefore originally been used in wastewater treatment. This article describes the results of pilot research on DynaSand filtration in the drinking-water production plant at Kralingen (Rotterdam), the Netherlands. The best filtration effiencies were achieved at low sand circulation rates. Wash-water flow can be limited to 4 per cent of the influent flow by modification of the washer element in the filter. The continuous filtration process can be controlled by air supply which directly adjusts the sand circulation speed. The advantges of continuous filtration, especially for small-scale plants, are uninterrupted operation and the absence of auxiliary backwashing facilities. Compared to conventional filtration the disadvantages are: higher wash-water losses, higher building height, and the need to include compressors and air-lift equipment.