NY METOD FÖR SPOLNING AV SNABBSANDFILTER MED VATTENSTRÄLE / New Method for the Flushing of Rapid SandWers using High-speed Water Jets
There is an increasing need for rapid sandfilters in sewage treatment plants due to more stringent requirements on the quality of the treated water. Besides sandfilters could possibly be used for other treatment processes such as chemical precipitation or denitrification. These factors imply a heavy load of suspended particles on the sandfilters making the flushing of the fikers very important. A new patented method for flushing is being developed with potemially both technical and economical advantages compared to the conventional method of backwashing. The new method utilizes strong water jets impinging on the filtersand from above fluidizing part of the sand and thus washing it. The paper will first discuss the principle of the new method. The emphasis is, however, on some important hydraulic problems related to an optimum design and operation of the new filter. The first issue concerns the interaction between a water jet and the sand – i.e. the extent of the fluidization. Results from laboratory studies the penetration depth of the water jet are presented. The second issue concerns the flushing effect of different operational uses of the jets. Results in terms of permeability from prototype studies at a sewage plant reported. Finally a brief prototype study of the retention capacity of the sandfilter for suspended particles is reported. “Complete abstract not presented.”