Costly rate controllers are replaced with fixed orifices and therefore, would make the units economical particularly in large water works involving batteries of filters. The filtered water header pressure may be regulated by a throttle valve which discharges to filtered water reservoir. A fixed orifice is built into the effluent piping for each filter so that no filter after washing will take an undue share of the flow. In the effluent controlled type of filters, the filter effluent lines are connected to a common header. Declining-rate filtration systems are either in-fluent controlled or effluent controlled. In declining-rate filtration, the rate of flow through the filter is allowed to decline as the rate of head loss builds up with time. Declining-rate filtration with fixed or variable head When the head or effluent turbidity reaches a preset value, the filter is back-washed. Pumps or weirs are used for in-fluent control. In constant-rate variable filtration head, the flow through the filter is maintained at a constant rate. Constant-rate Filtration with variable head Pumps or weirs are used for in-fluent control whereas an effluent modulating valve that can be operated manually or mechanically is used for effluent control. They are either in-fluent controlled or effluent controlled. In constant-rate filtration with fixed head, the flow through the filter is maintained at a constant rate. and variable- declining-rate filtration.constant -rate filtration with variable head,.The principal filtration methods now used with reference to the rate of flow through gravity filters may be classified asĬonstant-rate of filtration with fixed head, Multimedia filters typically consist of a layer of anthracite over a layer of sand over a layer of garnet. Dual- medium filters usually consist of a layer of anthracite over a layer of sand. Typically sand is used as the filtering material in single medium filters.
There are a number of different types of Rapid sand filters depending upon bed depth (e.g., shallow, conventional and deep bed) and the type of filtering medium used (mono-, dual-, and multimedia).Ī further classification can be made based on the driving force as gravity Water Filters or pressure Water filters. Water Treatment Filters in which filtration and backwash operations occur simultaneously are classified as continuous. Water Treatment Filters that must be taken off-line periodically to back wash are classified operationally as semi-continuous. In Rapid sand water filter the complete filtration cycle (filtration and back washing) occurs sequentially. Rapid sand Water treatment filter does not use biological filtration and depends primarily on mechanical straining, sedimentation, impaction, interception, adhesion and physical adsorption. The mechanism of particle removal also differs. The Rapid Sand Filter (RSF) water treatment equipment differs from the Slow Sand Filter water treatment equipment in a variety of ways, the most important of which are the much greater water treatment filtration rate and the ability to clean automatically using back washing.