Sources of Pure Water.

Sources of Pure Water.

At a dinner of the Medical Union, the oldest medical society in Buffalo, at the Saturn Club recently. Dr. J. L. Leal, of New York, a water expert, delivered an address on the methods of purification of water. Dr. Leal first referred to the necessity of having wholesome drinking water because of the important part it takes in human economy. He then pointed out the impossibility of finding pure water supplied by nature. Water derived from condensation, in the form of rain and snow, becomes contaminated before it reaches the earth and more so as it flows along the surface of the ground. Passing into the earth it becomes known as ground water and usually reaches a high degree of purity, but here, too, there is danger through too rapid displacement of the water, or by reason of crevices of bringing it to wells and springs before the dangerous elements have been eliminated. Many severe epidemics have been traced to wells and springs. The water found in brooks, rivers and lakes, flowing along the surface, is, of necessity, more polluted than the ground water although not containing so much organic matter, and being much softer and more agreeable to the taste, is more useful for public supply. Dr. Leal then took up the various systems pf purification of water, including sedimentation, slow sand filtration, rapid mechanical filtration with coagulation, ozonation and sterilization or disinfection. “Sedimentatin,” said he, “is based upon the principle tliat still water will purify itself. The system is very old, having been practiced in ancient Babylon and Egypt. The object is to remove suspended matters from waters otherwise unfit for public use. The ancients had no knowledge of the sanitary effects of the process. The factors entering into the process are time, sunlight, oxidation and gravity. Time is the most important, because by it opportunity is given to these factors to perform their functions. Storage should be of sufficient capacity to allow the necessary time. The effect of sunlight is to rapidly destroy bacteria on or near the surface. Oxidation takes place under favorable circumstances—bacteria sink to the bottom, either by their own specific gravity or are carried down by particles of organic or inorganic matter, where they either remain quiescent or die, or are devoured by the infusoria and other animals of a low type. Under favorable circumstances as good results may be obtained by this process as by filtration. By slow sand filtration, which was first used in London in the year 1829, an attempt is made to imitate artificially the natural filtration of ground waters through the soil. It consists of beds of gravel and sand and underdrains, so constructed that the filtered water is collected and led to the reservoir or well. The object for which it was first used was the removal of turbidity, the science of bacteriology not then being known. It was looked upon simply as a strainer. It is known now, however. that the straining effect has but little importance. Upon the surface of the sand is formed a deposit composed of bacteria, broken down organic matter, and also inorganic matters. This not only forms a very fine strainer, but by bacterial action the invading disease germs arc destroyed and organic matter is split up into its nitrogenous and carbonaceous elements resulting in carbondioxides and nitrous and nitric acid, forming nitrites and nitrates, which are harmless products of bacterial action. This system has done satisfactory work, but to-day better results can be accomplished at much less expense and requiring much less area. The rapid mechanical filtration with coagulation system is an attempt to secure the results obtained by slow sand filtration much more rapidly and with much less area and more cheaply. Its object in the first place was to clarify the water. It has been found, however, that it can give actually as good results baeteriologically as slow sand filtration. It is, however, not a bacteriological process, but a nurely mechanical and chemical one. The water is first coagulated in what is called the coagulation basin by the addition to it usually of sulphate of alumina. By its addition to the water hydrate of alumina is formed, which is a flocculent, gelatinous mass permeating the water which for the most part sinks to the bottom of the coagulation basin, carrying with it suspended matters, including bacteria. Its action is similar to that of the white of an egg added to coffee to clear it of its grounds. From the coagulation basin water flows upon a scries of small filters usually about 24 by 15 feet, which remove the remaining hydrate of alumina and suspended matters and deposit them upon the surface of the sand. The water filters through the sand and gravel to a system of underdrains conveying it to a reservoir or well. There are about 600 plants of this type in the United States, compared with less than twenty slow sand filter plants. There can be no doubt that this system will be one of the most useful in the future in conjunction with sterilization. To the best of my knowledge and belief, ozonation, up to the present time, has never been made practical for treatment of water supplies, except possibly for a limited quantity. It may be that some time the difficulties found in the utilization of the process can be overcome, though there does not seem to be any prospect of it at the present time. The latest development in the purification of water is called sterilization or disinfection. It is used in the present time in many cities in the United States and in some in Europe and Asia. In consists in the addition to water of minute quantities of oxychloride of lime. The process has been used in the sterilization of sewage and for general disinfection purposes in many places. It was also used temporarily in a typhoid-fever epidemic at Maidstone, England. The first time, however, the process was used as a continuous method of water purification was at Boonton, N. J., in the reservoir of the Jersey City water supply. The effect of the addition to water of oxychloride of lime is to immediately destroy the vast majority of bacteria present in such water and the later destruction of the greater proportion of those escaping the first explosion. There is no material change in the quality of the water after treatment, such as would in any way interfere with its use for potable and manufacturing processes. The only change taking place being a very slight increase in hardness, a decrease in free carbonic acid and the destruction of bacteria, both of which are most desirable. The results obtained are phenomenal, water with a raw water counts of from 20,000 to 250,000 or over bacteria per cubic centimeter being rendered sterile. There are no tastes or odors if the plant be properly run. It is a simple process, easy of application and certain in its results. At the same time, however, it requires trained technical knowledge and skill to install and operate a plant. It has been on account of the lack of this that in all cases satisfactory results have not been obtained. It is certain to destroy the bacteria, especially the pathogenic class for hygienic purposes, and therefore is the most valuable, the cheapest and the most effective system known. The esthetic side of a water supply, however must be considered and sterilization does not remove turbidity or color. It is applicable in all cases of emergency to any water. It is applicable alone to any water that is estlietically satisfactory. It is a most valuable, and I may say even a necessary adjunct to other methods of purification. Where water supplies are obtained from large lakes or reservoirs, affording ample opportunity for sedimentation this process as a supplement makes the system all that can be desired. Where the water is of such a character that filtration is necessary, then the system, in conjunction with rapid mechanical filtration, seems to be the process indicated.”

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