Are Filtering Beds Correctly Constructed

Are Filtering Beds Correctly Constructed

Dr. Paul F. Bussman, of Buffalo, N. Y., in a very unassuming manner writes a letter to the Scientific American, in which, not without deprecating any disposition to dogmatise on the subject, and professing himself one who has never studied engineering in any of its branches, he asks: "Are our filtering beds constructed correctly or on correct principles?"

After stating his belief that they are not, he writes: “The object for which filtering beds are constructed is to furnish pure water, and not t oobtain all the foreign matter held in suspension by the water, and then, when you have obtained the same, to know that you have something that you absolutely do not want and some pure water. As far as I know, and in a general way, filtering beds are constructed byplacing conducting pipe having broken joints on the bottom of a reservoir, or by covering them with some suitable material having perforations, and upon this layers of broken stone of large size, broken stone of smaller size, gravel, coarse sand, and lastly a bed of fine sharp sand—these several layers to be about one foot in depth, but the last one from three to five feet. Water having foreign matter in suspension is pumped upon this bed and allowed to pass through, and the water then used for final distribution through the city’s mains. When one portion of water has passed through, another is pumped on, and so on until the surface of the bed becomes clogged or choked up from the foreign matter held in suspension, and which has accumulated from day to day for a variable time, according to the condition of the water. The surface of the bed is then scraped off, and either washed and replaced or is replaced with entirely new sand. This bed certainly catches all the foreign matter held in suspension, and, if this was the object for which it was constructed, it would work to perfection: but, as the object is to furnish pure water, it docs not furnish all the pure water, but only a portion. The object is to furnish all the pure water, and no foreign matter or dirt. The water placed upon the filtering bed must pass through the same; there is no other outlet. Now, if the water could pass through the filtering bed, and at the same time have an outlet for the foreign matter held in suspension, then there would be no accumulation of foreign matter."