Methods of Operating Pittsburgh’s Filtration Works
In July, 1910, George A. Johnson, consulting engineer of New York, was engaged by Hon. W. A. Magee, mayor of Pittsburgh, Pa., to make an investigation of certain features of construction and existing methods of operation of the slow sand water filtration works completed by that city in 1908 at a total cost of some $6,000,000. R. S. Weston, of Boston, was associated with Mr. Johnson on studies relating to the chemical phases of the problem. The practical result of Mr. Johnson’s investigations are set forth in the last annual report of Charles A. Finley, superintendent of the water bureau. Abstracts from Mr. Finley’s report follow: “It is noted with satisfaction that the total operating and maintenance charge for the year is almost $50,000 less than the cost of last year’s operations. The total for the past year was $818,626.12; for the previous year, $868,141.07. Most oi this saving is due to the improved methods of operating the filtration plant, the saving in operation at this plant during the last year being about $40,000. The operation of the filtration plant for the past year has been attended with gratifying results from a financial and sanitary point of view, due to the fact that, with the improved methods of sand handling instituted last year, we were able to operate the plant about $40,000 cheaper than the cost of operating by the methods previously employed. It appeared, from an examination of the records, that the operating cost of our plant was unnecessarily high. It also appeared that, at certain seasons, we got unusually small yields from filters between cleanings. The question thus naturally divided itself along two lines: First.—A study of the actual operating conditions within the filters, such as methods employed for sand handling, etc. Second.— A study of the physical and chemical properties of the river water, for the purpose of devising methods of eliminating from the river water the causes of the excessive clogging prior to its application to the sand filters. The first question has been handled and investigated by Mr. Johnson. The second question has been handled and investigated by Mr. Johnson and Mr. Weston, acting in conjunction. These investigations began in July, 1910, and extended over about 18 months’ time to January, 1912. The principal changes in operating conditions within the filters were the introduction of the process of ‘raking’ the filters between ‘scrapings,’ thereby securing additional yields from the filters at less expense than by continuous scraping, and a change in the process of restoring sand from restoring by machine to restoring from open hose lines under water. The study of the physical and chemical properties of the river water was, of necessity, complicated and protracted, due to wide variation in the character of the water on account of seasonal and other changes. The investigations were continued until all the different types of water had been encountered, a large amount of data was compiled, careful study made thereof, and conclusions drawn therefrom. In line with the conclusions a system for the preliminary treatment of the river water was designed, and the necessary contract plans prepared for the construction of the same. The result of these investigations indicates that the daily capacity of the plant can be increased from 125,000,000 gallons to 200,000,000 gallons without the construction of additional sand filters. The amount of water yielded by a filter between cleanings is an essential factor in the increased capacity of the plant. The prime object of preliminary treatment is the assurance of the necessary yield between cleanings. With this yield assured, the rate of filtration, or the amount of water filtered daily through each filter, can be increased so as to produce a total daily yield of 200,000,000 gallons, and still maintain the economy of operation in sand handling. To arrive at this total daily capacity by slow sand filters, without preliminary treatment under the present conditions, would require the construction of about 90 additional slow sand filters of one acre each. The approximate cost of this installation would be over $2,000,000, not including the necessary land. The annual saving in sand handling atone is $40,000 with the plant as it now stands, and if we consider the difference in cost between the extension of the present sand filters without preliminary treatment, and the introduction of preliminary treatment without extending the sand filters, as developed by the investigation, said difference being, in round numbers, about $1,600,000, exclusive of land, and allow 5 per cent, annually on this saving, it amounts to $80,000 which, with the $40,000 saved in operations, makes a total of $120,000.”
Typhoid Fever in Pittsburgh
Before the installation of the water filtration works Pittsburgh had a typhoid fever death rate of practically double that of any other large American city. As set forth in the last report of C. A. Drake, superintendent of filtration, the first filter unit was started in December, 1907. All of peninsular Pittsburgh was receiving filtered water exclusively in October, 1908, and all of the south side, except the twentieth ward, in February, 1909. The present typhoid fever death rate in the filtered water district shows that the purified water supply may well be included among the very safest supplies of the world. The following table, showing typhoid fever statistics in certain important American cities, shows what the Pittsburgh filtration works under skilled supervision, and with the final filtered product sterilized with hypochlorite of lime, has done in the line of cutting the typhoid fever death rate to a practical minimum. The results achieved at Pittsburgh in this line are by far the most gratifying and spectacular ever noted in the history of water purification in this country. Following is the typhoid fever death rate in certain American cities per 100,000 population:
*Filtered water district. Includes 410,000 of a total of 545,000 inhabitants of Pittsburgh.