the fact that under certain conditions sewage may be utilized with profit and to indicate in general terms how this may be done.

In the arid and semiarid portions of the West sewage utilization is of especial importance, for there every drop of water, especially during the summer season, is needed for the production of crops. The relatively small flow of the streams, combined with the warm climate, renders sewage especially obnoxious if not properly cared for, so that considerations of health and comfort are added to those of increased land values due to complete utilization of the water supply. The introduction of sewage irrigation in the West is more easily accomplished than in the East because of the general employment of water in agriculture. The first use of sewage in this connection in the West was probably at Cheyenne, Wyoming, in 1883. It has also been used at Colorado Springs and Trinidad, Colorado, at Fresno, Pasadena, Redding, Los Angeles, Santa Rosa, and Stockton, California, at Salt Lake City, Utah, and at Helena, Montana.

The popular idea, not only with us here at home but very largely abroad, is and has been that anything and everything connected with sewerage and sewage disposal is of so vile a character that it must be kept entirely out of sight. Out of sight, out of mind, has been the universal principle thus far. The immense aggregation of population in cities, however, by forcing the subject upon the attention of urban communities, has served to modify somewhat this popular misapprehension. At the present time the few persons who have thought out the rational view of these subjects hold that the old notion was, like many old notions, essentially wrong. Sewage is a great fact of existence, and the proper way is not to ignore it but to meet the problem on its merits, the same as other difficulties are met and overcome. In this spirit, in England, at any rate, it has become quite common to build the necessary works connected with sewerage and sewage disposal as ornamental as possible, and in the United States this plan has been likewise followed in a few places.

Sewage purification was first attempted in England about forty years ago. At that time extravagant and, in the main, essentially erroneous views were entertained as to the possibilities of its utilization in agriculture. Especially was this true as regards the manufacture of artificial fertilizers from the sludge of various chemical processes. Large investments of capital were made and concessions granted by towns to private companies, practically all of which were for processes of chemical purification. With very few exceptions these investments have all proved a dead loss. The purification of sewage by chemical treatment at a commercial profit has been found impracticable. In the meantime land processes, which have developed contemporaneously with the chemical purification processes, have in every sense held their own, until at the present time it can be

said that under proper conditions a fair profit may be made by the cultivator from the utilization of sewage in agriculture.

About twelve years ago the author began to collect information in regard to the pollution of streams and the purification of sewage, with special reference to the conditions existing in the United States. At that time, aside from the work done by the Massachusetts State Board of Health and that just begun by the city of Philadelphia, very little information was available as to stream pollution in this country; necessarily one studying the subject must go to the foreign sources of information, and for this purpose nothing better could be found than the voluminous English sanitary reports, issued from time to time by various royal commissions and by a number of the large municipalities of that country. But since about 1886 the subject of sewage purification and its relation to the purity of streams has received much consideration in the United States, so that at the present time we have over sixty purification works in operation. American data are therefore accumulating rapidly, and we may hope in a few years more to have arrived at a full understanding of the more important principles involved in sewage purification and the prevention of pollution of streams as applied to our special conditions.

The conditions here are quite different from those existing abroad. In the first place, the streams are much larger, and so far as the production of mere effluvium nuisances is concerned they can take larger quantities of sewage without offense, although it ought not to be overlooked that since many of our streams are the sources of public water supplies the effect of sewage pollution may be even more harmful than though effluvium nuisances were produced, which, however unpleasant to the sense of smell, are not always the source of special impairment of health. Again, it may be pointed out that land, even in the immediate vicinity of large towns, is much cheaper here than abroad. In a number of cases in England the lands utilized for sewage irrigation have cost as much as £400 to £500 per acre, whereas with us frequently suitable lands can be purchased within practicable distance of towns for from one-quarter to one-eighth of these figures.

The large amount of experience gained abroad should have weight and value. For this reason an attempt is herein made to present saliently the current European practice of sewage utilization. We have tried too often to work out for ourselves what is popularly known as the American method, ignoring the experience of others. We may thus attain unto knowledge in the course of time, but meanwhile many unprofitable investments will be made and money and time will be unnecessarily lost. In this respect the conditions are similar to those seen in the development of ordinary forms of irrigation in the West, where frequently expensive works have been built and operated without a knowledge of the water supply or other conditions. A very

cursory study of Old World irrigation would have saved considerable loss and resulted in more satisfactory results than those now attained. In many of these older countries, having physical and climatic conditions almost identical with our own, methods of agriculture and of controlling and utilizing water have been developed through the trials and failures of unnumbered generations. We are merely repeating many of their mistakes, and are only gradually coming to appreciate the fact that a more complete knowledge of the experience of the rest of mankind would be of incalculable value to us.

GENERAL PRINCIPLES.

The more important of the general principles discussed in this paper are brought together at this point for convenience of reference:

(1) Sewage purification is an imperative duty which municipalities owe to the owners of riparian rights, and which can not be neglected by municipalities without such an infringement upon those rights as it is now well established may be prevented by legal process.

(2) Sewage utilization should go hand in hand with purification. When operated with reference to all the necessary conditions, a proper degree of purification may be attained as well as satisfactory utilization.

(3) The proper method of utilizing sewage is, for purposes of irrigation, by means which do not differ, except in matters of detail, from those of ordinary irrigation as practiced abroad for centuries.

(4) In order to utilize sewage to the best advantage, the towns should construct, at their own expense, intermittent filtration areas on which the sewage may be efficiently purified when not required for use in agriculture. Farmers utilizing sewage in agriculture should be required to take it only as needed for the best results on crops.

(5) The theory of the action of intermittent filtration is in effect the theory of purification as effected by broad irrigation, the difference between the two being chiefly a matter of detail.

(6) In the purification of a strong acid sewage from manufacturing towns it may sometimes become desirable to treat the sewage by a chemical process before utilizing it in agriculture. For this purpose lime is the chemical commonly used.

(7) In case the effluent from sewage purification works or areas is to be passed into streams which are the source of drinking water for towns farther down, the degree of purification should necessarily be high. The experiments of the Massachusetts State Board of Health show that there is no trouble in removing from 95 to 99 per cent of the organic impurity, as indicated either by the chemical constituents or by the bacteria. When as much as 99 per cent is removed, the sewage becomes chemically purer than the water of many wells, and there is, so far as known, absolutely no reason why it may not pass safely into a stream used as the source of a public water supply.

(8) Intermittent filtration areas are best constructed of coarse mortar sand, as shown by the experiments of the Massachusetts State Board of Health.

(9) Intermittent filtration is chiefly a biological process, in which the nitrifying organisms, with the assistance of oxygen and the minerals naturally in solution in sewage, resolve objectionable organic matter into mineral nitrates, etc., the whole process, when properly conducted, taking place without the production of objectionable odor. The conditions for successful treatment are, generally, intermittency of application and open spaces in the filtering material to which common air may easily gain access. Such filters may be expected to purify from 30,000 to 100,000 gallons per acre per day, the amount depending upon the quality of the material in respect to sand and water content, as defined by the studies of Mr. Allen Hazen.1

(10) Sewage may be purified by broad irrigation at all seasons of the year at any place where the mean air temperature of the coldest month is not lower than about 20° to 25° F., while by the use of intermittent filtration it may be purified fairly well down to a limit of 18° to 20° F., provided the sewage reaches the purification area at a temperature not lower than about 45° F.

(11) From the experience gained abroad it is clear that we may successfully cultivate almost any of the ordinary agricultural productions of the United States on sewage farms, due regard being had in every case to the special conditions required for each particular crop. (12) The most efficient purification of sewage can be attained by its application to land.

(13) On properly managed sewage farms the utilization of sewage is not prejudicial to health.

(14) In comparing the results of sewage utilization as thus far obtained in the United States with the results obtained abroad it is clear that, generally speaking, we have not been specially successful. As one chief step toward a remedy for this we need to create in this country a class of sewage-farm managers who are thoroughly familiar with all phases of the question. Thus far the management of American sewage farms has been usually in the hands of committees of municipal councils having little or no knowledge of the real governing conditions.

(15) The experience in England, Germany, and France, and also that gained in this country, all points to intermittent filtration relief areas, on which any surplus sewage not required in agriculture may be purified, as the rational method of procedure.

1From 30,000 to 100,000 gallons of ordinary raw town sewage may be so thoroughly purified that it may be admitted to streams from which public water supplies are taken. If a less thorough purification is required, or if the sewage has been previously treated with lime, from 200,000 to 300,000 gallons per acre per day may be successfully purified.

SEWAGE DEFINED.

Before proceeding to the main discussion, it is necessary to know the meaning of the terms in common use. By sewerage we refer to the general practice of removing the liquid and solid wastes of the human economy, as well as the washings of streets and manufacturing wastes, by water carriage. A sewer is the conduit in which, by the medium of water, such removal is effected. Sewage is the generic term, not only for the combined water and waste matter flowing in sewers, but also for the mixed solid and liquid matter handled either by pail or by pneumatic systems.

Ordinary city sewage contains a great variety of ingredients in addition to the waste water from kitchens, baths, laundries, and other domestic offices. In manufacturing districts it may contain the refuse substances of various manufacturing processes, the whole diluted with a considerable amount of water, to which, in rainy weather, in towns with combined sewerage systems, is added a large amount of sand and earth and organic matter from the street washings. With separate systems of sewers street washings are excluded, and the sewage, by reason of containing the house drainage only, has a much more uniform composition than is found in the sewage from combined systems; whence it results that the sewage from separate systems is somewhat more amenable to treatment, for two reasons: (1) because of more uniform composition; (2) on account of less variation in quantity. In case sewage is to be purified at sewage-disposal works, both these considerations lead to decrease in first cost of the works as well as to decrease in annual expense of operation. In case of utilization of sewage for irrigation, the same considerations lead to certainty and ease in the utilization as well as to decrease in the expense.1

In American cities, which use at least 60 to 100 gallons of water per capita per day, sewage is considerably more dilute than in foreign cities, where from 30 to 50 gallons per capita is more nearly the daily allowance. As remarked by Mr. Mills in the special report of the Massachusetts State Board of Health, we may say that the sewage of the average American town will contain something like 998 parts of water, 1 part of mineral matter, and 1 part of organic matter. The mineral matter, as it ordinarily exists in sewage, can not be considered as specially harmful, and from a sanitary point of view the object of

1 See Sewage Disposal in the United States, Rafter and Baker, Chapter VIII, "General data of sewage disposal," and Chapter IV, "The self-purification of running streams," etc., for detailed discussion of fundamental points only briefly touched upon here.

2 In all cases by gallons is understood the United States gallon of 231 cubic inches, or 0.13368 cubic feet.

3 For information as to the use of water in American cities and towns in detail, see the Manual of American Water Works. A few cases are cited on page 16, following.