To provide a flocculation filter which can obtain filtered water whose SDI is less than 3.0 even at the early stage of filter treatment and then all along.
This filter comprises a means to add a flocculant to suspended matter in water to be treated and a filter column for removing the suspended matter. The filter column has one or more filter medium layers made up of a granular filter medium with 18 to 30° angle of repose. Besides the filter column has 40 to 60% voids with regard to the filter medium layer before starting the filter treatment and preferably, has a layer made up of the granular filter medium which shows 0.5 to 5.0% degree of consolidation defined by the following formula, in the case where the liquid is run through the filter medium layer with 1,000 mm height of the filter medium layer at a filtration rate of 20 m/h:, wherein compressibility(%)=((height of filter medium layer before water running-height of filter medium layer after water running)/height of filter medium before water running)*100.
COPYRIGHT: (C)2009,JPO&INPIT
Kazuhiko Shimizu
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Tadashi Takahashi
Tomoo Katsumata