THE DEVELOPMENT OF FILTRATION FOR PURIFICATION OF TURBID RIVER WATERS
The process of filtration for the removal of sediment, turbidity and other impurities from river waters has been practiced in Europe for many years. The first effort made by the American people in this direction was in 1866, when the late J. P. Kirkwood, a civil engineer, was sent to Europe to study the methods in practice there and apply them to the Mississippi at St. Louis. Mr. Kirkwood’s report was remarkable in that it brought out every detail in the successful purification of the European waters as they existed at that time. The plans he submitted for the St. Louis water were not adopted, possibly the cost was too great and the benefits of purification were not so well understood as they are to-day. And again it may be that the tests that were made on a small scale did not give the results expected. This, however, is supposition, as the results of the tests were never made public. Although Mr. Kirkwood’s designs for St. Louis were never carried out, several filters were built as the result of his work and report. From his plans a filter was built at Poughkeepsie, N. Y., where the conditions were similar to those in European cities; this was the first and most successful plant of any of the early purification plants in this country. Afterward a number of cities installed filters, some were successful while others were failures; the failures were due to the failure to provide sufficient filtering area, to the modification of the design which did not prove beneficial, and to the fact that some of the waters carried too much suspended matter. The public at this time was becoming more interested in filtration and Prof. Nichols, of Boston, made some experiments and wrote an interesting report on the subject. This report led to experimental trials at Boston, Louisville and other places, but on the whole they were not successful and did not lead to any improvements in the method. About 1884 a process was patented by the late J. W. Hyatt that was destined to play a large part in the future development of the process. The main features of the method were the addition of a coagulant, passing the water through a layer of sand so arranged that the water could be reversed and the agitation of the sand by means of a rake or other mechanically operated device. This was the beginning of the mechanical filter, sometimes called the Rapid Sand or American Filter. The European filters were what are called Slow Sand Filters, and the mud that was collected on the surface of the sand had to be removed by hand, usually with shovels. Mr. Hyatt’s method met with some success and quite a number of plants were installed in cities, towns and paper mills. The study of the purification of water and sewerage was receiving more and more attention and in 1890 had reached such a point of perfection that the outbreaks of typhoid fever in the city of Lawrence Mass., had been traced to the Merrimac River, from which the city received its water supply. A sand filter was proposed to purify the water supply and in 1893 was put into service. This was the first filter built in America for the express purpose of reducing the death rate of a city. Comparing five years before and five years after its use, statistics show that there was a 79 per cent, reduction in the typhoid fever death rate. The Ohio and other rivers that carried clay began to be studied. The clay in some of them would hardly settle in water at all, and the removal of this clay was important on its own account, for no water could be considered satisfactory or purified so long as it remained turbid. Alum had been very generally used as a coagulant and in fact about the only one used up until 1903, when the Mississippi was successfully treated at St. Louis with sulphate of iron and lime. There is an approximate relation between the turbidity and the amount of coagulant necessary to completely coagulate or collect the clay and suspended matter that is in the water. The chemical composition as well as the size and weight of the suspended particles will cause the amount of coagulant to vary, but generally speaking, the greater the turbidity the greater will be the amount of coagulant necessary to envelope the clay particles. The amount of clay removed during the passage of a water through a sendimentation basin after coagulation, depends: On the time required for its passage, the design of the basin and the character of the clay; but in all cases enough should be left to form a satisfactory mud cover or “Schmutzdecke” on the sand in the filters. No rapid sand or mechanical filter can be expected to give a high bacterial efficiency unless the water is thoroughly coagulated and the formation of the mud cover or schmutzdecke is perfect. The operation of a mechanical filter plant at its highest efficiency requires care and attention. Managers, superintendents and operators should remember that a plant cannot be built fool proof nor automatic and that in their carelessness and neglectfulncss they are tampering with the health of the population that the plant is supplying. If you are familiar with the process you can impart what you know to others and in that way assist in bringing the public up to the full realization of what good pure water means to them. Too little importance is attached to the water works by the general public; they don’t seem to realize that judgment has to be used and that care and constant watchfulness is necessary on the part of the operators to make it possible for them, the public, to drink water from the faucet in their homes without fear of typhoid fever and other diseases. To the minds of some, all that the men at the water plant have to do is to watch the water run by and draw their little pay. A complete sanitary analysis of water consists of four parts: The physical, the microscopical, the bacteriological and the chemical. Sticb an analysis is intended to show whether a water would cause sickness if used for drinking purposes, whether it contains anything distasteful and whether it is fit for boiler and laundry use. The works of Messrs. Hazen, Whipple, Mason, Prescott, Winslow, Sedgwick, Jordan and others go into this subject in detail, and have done much toward bringing the process of filtration up to the place it holds in the sanitary science of to-day. One of the many important things that should be constantly borne in mind is this, that if the public water supply of any city has been more or less polluted for several years the inhabitants generally acquire a certain immunity against the water-borne diseases in the water. The death rate from infectious water-borne diseases may be high, but it effects persons of low vitality and invalids, while the general masses acquire that immunity. Now, if this polluted water supply is purified for some time, the general mass of neonle slowly lose that immunity and the death rate is much lower than it was before. Then, if the water supply that has been satisfactorily purified for several years becomes generally polluted there is a possibility of an epidemic of water-borne disease in that city owing to the fact that they have more or less lost their immunity for those diseases. Operate year filters at their highest efficiency and operate them all the time.
*Paper read at convention of the Tri-State Water and Light Association of the Carolinas and Georgia, Asheville, N. C., June 16-19, 1915.