Deep-bed filter and method for filtering

摘要

A filtration method and apparatus for removing contaminants from liquids, including a deep bed filter comprised of either a single media layer or of two or more vertically superimposed, substantially distinct, contiguous layers of filter material. In the plural layer deep bed filters the lower layers typically consist of materials such as sand or anthracite, which are inherently comprised of nonuniform filter granules, even when graded or sieved to within a fairly restricted mesh size range. The upper layer in the plural layer filters is comprised of filter media granules having substantially identical configurations and sizes to achieve a high layer porosity for reducing the rate of back pressure buildup during the filtration cycle. Additionally, the media granules of the upper layer preferably have a specific gravity of between about 1.05 and 1.4, are preferentially hydrophilic, i.e., water-wetted, as opposed to preferentially oleophilic, and are preferentially cylindrical. One specific example of a filter material having all these characteristics includes hollow glass tubes sealed at both ends. Such materials may also be used advantageously as the sole material in a single layer deep bed filter.PP The method includes backwashing the filter by flowing liquid upwardly through the filter media to expand the layer or layers substantially in situ. Afterwards, the layers are reformed. Due to the uniformity in size and shape of the filter material, the top layer is reformed with substantially the same porosity at its inlet surface as existed prior to the preceding filtration cycle.