The Dusenflo™ filter can be furnished with a homogeneous media, normally sand, or with a mixed bed media such as sand, anthracite or activated carbon. Water percolates downwards through the media at a flow rate of up to 30m/h (12 usgpm/sq.ft.).
Uniform bed media: The uniform bed media consists of fine sand having an effective size of 0.9 mm. With a homogeneous media, the filter retains particulate matter progressively in depth in the media mass instead of in the layers only. Cleaning a homogeneous bed filter requires air and water simultaneous backwashing.
Mixed bed media: Mixed bed filter are normally used when a fine media is required. The mixed bed media normally consists of a layer of fine sand, which supports an upper layer of larger particles such as anthracite. To avoid carryover of anthracite during backwashing, air backwashing or fluidizing will alternate with water backwashing according to a defined flow rate and sequence.
The underdrain system: A specially designed underdrain system allows the introduction of air and water to fluidize and scour the complete filter bed. Backwash air is used to vigorously stir and vibrate the media particles while backwash water expands the filter bed. Individual grains of media collide with each other, resulting in a scrubbing action, which effectively detaches solids. Backwashing with air and water is made feasible through the use of specially designed nozzles evenly distributed over the underdrain surface. Easy to install, the heavy-duty underdrain system lends itself well to upgrading and retrofitting filtration plants.
Underdrain nozzles: The underdrain nozzles are specially designed to allow backwashing with air and water. The nozzles slots are sized to prevent the escape of the media; the nozzle head is attached to a tube slotted at its lower section through which air is introduced. Depending on the media that is used, nozzles can be provided with slot openings ranging between 0.2 and 2.0 mm.
Surface washing: During the backwash cycle, retained solids scoured from the media are directed to the backwash water gutter by a surface sweeping action of flushing water introduced from the clarifier. This feature eliminates the need for transversal collecting troughs.