Licence: Public Domain Mark
Credit: The purification of sewage and water / by W.J. Dibdin. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![the top. Suggestions have been made to aerate a filter by blowing air from time to time into the bottom of the filter, and thus forcing it up through the bed. Such are the schemes of Lowcock in England, and Waring in America. Instead of thus using force, the inventor lets the air find its way into the filter in all directions, top, bottom, and sides. In a filter constructed with coarse material at the top, graduating to fine at the bottom, a slow stream of sewage amounting almost to drop by drop, allowed to fall on any particular portion of the surface will slowly wend its way downwards until, if there be no obslruction, it will arrive at the bottom and flow away. In passing slowly from fragment to fragment of the filtering medium, the suspended particles will be left behind, and also a large proportion of the foul matters carried in solution, the extent depending upon the fineness of the medium, and the rate of travel of the water. The organic matter so taken up by the filter, if worked con- tinuously, under ordinary conditions, will accumulate and choke the pores; and, becoming putrescent, render the whole process a failure. To overcome this difficulty, it has been proposed to ensure a constant supply of fresh air which will support the life process of the bacteria, and if the rate at which the sewage is supplied be properly regulated, the inventors hope that the process of purification will continue indefinitely. In order that the air should be thus introduced, the filter is built with perforated walls, and from some of these perfora- tions air inlets are carried into the whole substance of the filter in all directions and at all depths. Such a filter may be described as answering the same object as a lung in the animal economy, the air being taken up by a multiplicity of chambers, and thus utilised to oxidise the waste organic matter as it passes through the thin-wra]led vessels which are pervious to the oxygen of the air as well as to the carbonic](https://iiif.wellcomecollection.org/image/b21966734_0160.jp2/full/800%2C/0/default.jpg)
