THEORY AND OPERATION OF MECHANICAL FILTERS
While much of the information contained in this paper is admittedly an old story, especially to the Water Analyst and Bacteriologists, it will be useful to reiterate the facts for the benefit of the ever-increasing number of filter operators who, as a matter of fact, have little or no opportunity of gathering from various sources the information herewith presented. The mechanical filter does not depend upon its sand and gravel filtering bed alone for the high efficiency obtained. Coagulation and sedimentation are also essential features of the process and possibly least understood by the operator. Coagulation is produced by the introduction into the raw water of a soluble, harmless, mechanical salt, capable of decomposing when brought into contact with alkaline salts into an insoluble hydrate technically known as “Coaguluum.” There are three soluble salts used; i. e., Sulphate of Alumina, Alum and Sulphate of Iron.
The following reactions occur when any of these come into contact with alkalinity which may be native in the water or may be supplied through introduction of alkaline salts; commonly Soda Ash or Hydrated Lime.
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