PROGRESS OF WATER PURIFICATION

PROGRESS OF WATER PURIFICATION

A report under the title “General Statistics of Cities, 1915,” recently issued by the Census Bureau, brings out in a striking manner the progress made by many American cities during a little more than a decade in respect to the improvement of their water supply. Of the 204 cities having more than 30 000 inhabitants in the fiscal year 1914-15, 155, or 76 per cent., owned their water supply systems. Seventy-three of these cities were operating purification plants in that year, and of this number 61 had either built or improved and enlarged their plants since 1903. During this same period there has been throughout the country a remarkable decrease in the death rate due to typhoid fever. Although this decrease has taken place in both urban and rural localities, it is noteworthy that in most of the large cities which have recently built or improved and enlarged their purification plants the decline has been greater—in some cases very much greater-—than the average decline elsewhere. For example, in Cleveland the typhoid death rate fell from 111 per 100,000 population in 1903 to 8.1 in 1914; in Philadelphia, from 72.3 to 7.6; in Pittsburgh, from 132.7 to 15; in Cincinnati, from 42.2 to 6.2; in Chicago, from 33.5 to 0.0; in St Louis, from 52.6 to 12; in Washington, D. C., from 48.5 to 11.9; in Minneapolis, from 41.1 to 12.5; and in New York City, from 17.1 to 6.3.

The history of the purification of water for public use dates from 1829, when some filter beds were used in connection with the water supply of London, England; but the discovery that slow sand filtration not only removed inorganic matter, turbidity, color, taste, odor, etc.—acting merely as a strainer-—but also removed nearly all the bacteria, was not made unti about 60 years later.

The first purification plant constructed in the United States was put in operation in Washington, D. C., in 1853. This was of the “sedimentation” type, which depends upon the force of gravity to carry down and deposit the c’av and si’t. Simitar plants were installed in Louisville, Ky., in 1879; Council Bluffs, la., in 1883; Dallas, Tex, in 1889, and Omaha, Neb., and Oshkosh, Wis., in 1890.

In the Omaha plant sedimentation was combined with coagulation, the latter process consisting in the introduction into the water of some chemical, usually sulphate of alumina,through the action of which the impurities are carried to the bottom. The first plant employing mechanical filtration was installed at Oshkosh, Wis., in 1890. This process like that of slow sand filtration, depends upon freeing the water from impurities by straining it through sand, lit the straining is accelerated by the use of agitating or stirring machinery. From 1892 to 1899, inclusive, purification plants, each involving one or more of these four processes—slow sand filtration, sedimentation, coagulation and mechanical filtration—were installed in ten other cities of more than 30,000 inhabitants.

In 1900 a p’ant for the purification of water by chemical sterilization was built at Mobile, Ala. This process consists in the addition to the water of various chemicals which either kill the bacteria or make it possible to remove them by subsidence or filtration. From 1905 to 1914, inclusive, chemical sterilization plants were built in forty other cities of over 30,000, and at the present time more than half of the municipally owned water supply systems having purification plants are using this method, either exclusively or in combination with one or more of the other processes. There were 87 sedimentation reservoirs in 32 cities, treating 958,600.000 gal’ons a day; 527 slow sand filters in 17 cities, treating 598,700,000 gallons a day (subject to exception of Philadelphia); 439 mechanical filters in 35 cities, treating 469,600,000 gallons a day; in 26 cities a total of 492,100,000 gallons a day were treated by coagulation; and in 42 cities a total of 1,972,900,000 gallons a day were treated by chemicals. A part of the water treated by each process was also treated by one or more of the other processes mentioned.

As an illustration of the amount of -work sometimes performed by a purification plant, the following extract from page 95 of the 1914 report of the Sewerage and Water Board of New Orleans, La., is given: “During this year 8,147 million gallons were treated at the Carrolton plant, and 295 million gallons at the Algiers plant. This amount of water carried 21,300 tons of suspended matter, all of which was removed, and 3,800 tons of hardening constituents, about one-half of which was removed. Three thousand and fifty-eight tons of lime and 188 tons of suphate of iron were required to soften and prepare this water for filtration.

The reported cost of treatment per 1,000,000 gallons differed widely, owing to the varying amount of purification necessary in each case, and also to the fact that some cities included items as an expense of purification which other cities did not segregate from the general departmental expenses. Some of the cities and the methods of water purification they emp’oy, together with the cost per million ga’lons, are shown below: a, sedimentation; b, coagulation; c, slow sand filtration; d, mechanical filtration; e, chemical sterilization.

The degree of necessity of purification systems depends largely on the source of supply. The 82 cities having no such plants derived their water supply from a number of sources, as follows: Wells, 32 cities; rivers and smaller streams, 18 cities; lakes and ponds, 17 cities; two or more sources, 11 cities; springs, 1 city: water purchased from private corporations, 3 cities. Of the 73 cities employing purification systems, 60 obtain their water supply, wholly or in part, from rivers and other streams.

The growing solicitude for the purity and adequacy of the water supply is further indicated by the very considerable increase which has taken place during recent years in the amount invested in municipal water supply plants. The total capital invested in these plants in 1903-4, in the 105 cities of over 30,000 which owned, either wholly or in part, and operated their water systems, and for which data are available, was, in round numbers, $513,000,000, representing a per capita investment of approximately $29. In the fiscal year 1914-15 the number of such cities owning their p’ants had increased to 155, the total investment to $1,071,000,000, and the per capita inestment to approximately $38. The increase in the per capita investment during the eleven years thus amounted to 31 per cent.

The fact of prime significance brought out by the report is that an efficient system is now regarded by most cities as an economic necessity and hence is acquired, regardless of the cost.

No posts to display