City Water and City Waste

ON the Campagna, still dominating the soft Italian landscape, stand the great aqueducts by which water was brought to the imperial city. In the time of the Roman engineers, the necessity of an adequate supply of water was recognized, yet even to the present day quantity of water has been the first step, and quality, when considered at all, the second. In no place has this condition been more apparent than in the United States. England, by her wide-reaching systems of great reservoirs fed by the waters of small streams; France and Austria, by their mountain spring supplies, necessitating hundreds of miles of aqueducts, trailing their way from the upper slopes, through meadows and vineyards, to the towns and cities; Germany, with her enormous purification plants for treating polluted river waters, — all have taken more national interest in the problems of public water supply than has the United States. In this country there are hundreds of excellent water supplies, but there are other hundreds and thousands still existing in a most imperfect state, furnishing with every gallon of water the possibilities of disease.

Great bodies of men have concentrated in the cities during the last half century. With this concentration centres of population have emerged from the condition where every man’s water supply was his well, his sewage plant the cesspool in his own yard; and, with many another collective change, we have come to a common source of water and a common disposal of sewage. To guard the purity of the common water and to insure safe methods of sewage disposal is a great task, for without such guardianship grave and deadly danger is at the city’s side. A single failure of this sort may well recall the gravity of the problem.

In April, 1885, the town of Plymouth, Pennsylvania, contained some eight thousand men, women, and children. The general health was excellent, and the water supply, from a clear mountain spring far above the town, seemed unusually good. Like a whirlwind came the plague. Out of that eight thousand, eleven hundred and four contracted typhoid fever, and one hundred and fourteen died. Rich and poor alike were taken, and through every part of the town, highlands as well as lowlands, the fever raged. Whence came this terror? From a single case of typhoid, brought back from a great city whose polluted waters caused the fever. This case existed in one of the only two houses that could contaminate the water system. From this source came the decimation of the little town far below. The story of such water-borne epidemics as this, and the solution of the problem of prevention by the sanitary engineer, form one of the most fascinating chapters in the never-ending war against disease.

Disease is ordinarily caused by preexisting disease in man or another animal. Here is a bold statement that is far too likely to be forgotten. Typhoid fever and Asiatic cholera from the intestinal germs of former cases, scarlet fever and measles from the skin excretions of convalescing patients; yellow fever and malaria from the mosquito in which the disease germs pass a portion of their life; — case after case of the truth of this theory might be cited. Moreover, if we accept the germ theory of disease, we must believe that many classes of ailments owe their origin to certain definite microörganisms which belong specifically to each separate disease and to no other. It is well known that these bacilli or bacteria, entering the body, find there a comfortable lodging-place where they may grow and multiply. The various symptoms and periods of each disease correspond, it is believed, to differing stages of their existence. The alimentary canal furnishes a peculiarly favorable ground for the cultivation of certain of these microörganisms. Water is the chief substance to pass through this channel. Typhoid fever and Asiatic cholera are water-borne. What are the possibilities of disease in water, and how may prevention be secured ?

Of all possible sources of bacterial infection of water, sewage stands easily firstSewage, the collected organic wastes of community life, is the home of myriads upon myriads of bacteria. With the necessity for a common sewer has come the problem of such a disposition of sewage that there shall be no possibility of admixture with the water supply. The coast cities can use the sea for such disposal, but the great mass of our population is inland. Large towns and cities must depend on large bodies of water for their supply. The danger that these waters may contain pollution from sewage is one which should be avoided at any cost.

Each pipe and faucet bringing water into the private home or public fountain is a gate by which disease may enter, if proper safeguards are not placed in the way. Let us consider what barriers, natural and artificial, may be raised against such entrance.

Two classes of water are recognized by the sanitary engineer. Ground water is the first, in which class ultimately belongs the great body of atmospheric water falling to the soil. This water directly penetrates the interstices of the surface earth, and sinks to a greater or less distance. Surface water, on the other hand, is that water which strikes nonpermeable soil, and rolls from rocks or flows from clayey earths directly into streams or ponds. These larger bodies, as well as their visible supplies, are called by the same name, although they are fed to a large degree by ground waters from below. It is in the water on the surface of the earth that one finds the chief source of peril. The rushing stream or quiet brook gathers the various impurities along its road and disseminates them as it passes on, while, to add to the difficulty, other pollution may come from industrial and organic wastes sent forth from factory and town along the shore.

Ground water as it passes into the earth receives a natural filtration marvelously thorough in its action. In this straining and cleansing of the water entering the soil we find the first of the natural barriers placed against the foe. A porous earth is a storehouse of bacteria; the richer the soil, the more fertile and open the ground, the greater will be the multitudes of bacilli spread to an infinite extent throughout its masses, since here are found all the advantages to foster the life of the germ,—oxygen, moisture, and food. As the water passes down through layers rich in microörganisms, some filtration proper undoubtedly takes place. Vastly more important for purification is the fact that the bacteria in its path rob the traveling liquid of all organic matters, the food of the germs. This action is so effective as soon to make bacterial existence impossible. In consequence, the purity of the ground waters is marked; and when taken from deep cavities, by means of driven wells, they make a serviceable type of water supply. A possible hardness from dissolved inorganic matters, and a tendency to develop vegetable growths under the action of light, are two difficulties with such a source. Far more serious, however, is the fact that such a supply in most cases is small in amount, owing to the slight extent of the natural reservoirs.

The limited supply of ground water has forced the great mass of communities to the use of surface water. With this source the first point of defense must be the control of that territory from which the supply comes. No point in the chain of defense against the invading germ is of more importance than complete control and proper supervision here. The results of overlooking this necessity have already been noted in the case of the town of Plymouth; and widespread epidemics have often come from a single source of infection on the watershed. In Germany, England, and America it has repeatedly happened that in towns with two sources of supply, one pure and the other impure, those who used pure water have escaped, while those who used the polluted liquid have perished. More thoroughly to safeguard the Metropolitan Water Works System in Boston, for instance, neighboring towns and cities, whose drainage might even remotely affect the water, have been obliged to install sewage-disposal plants.

Geological conditions and the natural slopes of the land prevent many cities from using still waters collected in reservoirs or impounding basins, and they are forced to resort to more or less polluted lakes and rivers. Even under this necessity, how has it come about that so many water supplies are taken directly from polluted sources, without a single cleansing of the raw water? The answer in many cases must be that such systems were installed during the prevalence of the theory that “running water purifies itself.” This theory was based on the fact that fouled running water soon became bright and clear. The chemical analysis showed that less organic matter was present at the lower than at the higher point where wastes had entered. Moreover, the slight knowledge of bacterial water examination of that day was insufficient to show that the germs of disease had not disappeared between the two points to the same extent as had the other organic matter.

On the contrary, it is now known that storage water systems which keep potable water for periods of time in lake or reservoir have a purifying tendency. This purification is due to the fact that parasitic bacteria in the low temperature, the sunlight, and the scant food supply of a reservoir or lake where organic matter is practically absent, have at best a struggle for existence. Many must succumb, since disease bacteria of the water-borne varieties are adapted to the warmth and moisture of the alimentary canal. Such germs as these, accustomed as they are to an easy existence, die when brought into conditions where hardier organisms might survive.

No town placed on a river-bank and unable to obtain long storage need be forced to use polluted water, need be defenseless against the bacterial assault. One safeguard stands preëminent to-day: the filtration of water under such conditions as to remove not only its turbidity and color, but even its bacterial life as well. Water filtration proper, as opposed to sewage filtration, is a mechanical operation, a straining out not only of dust and dirt, but also of the infinitely small inhabitants of the liquid, these inhabitants being such tiny living creatures that half a million of them may float unseen in a teaspoonful of water. It is an interesting journey to pass through the different steps which are taken in the treatment of water by a system of continuous filtration.

To remove any grosser forms of residue, such as gravel and waste, the raw incoming water, known as the affluent, is turned into a great reservoir with massive sides, called the settling or sedimentation basin. Here it is allowed to remain until the impurities which would clog the filter have settled. When this has occurred. the upper layers of the water are drawn off into the filter proper, a great basin made of masonry or concrete, underdrained, and with an exit pipe at the bottom. This basin is filled with fine sand above a gravel layer, which in turn is supported by rock underdrains. The sand acts in a double capacity. The spaces between separate grains of sand are ordinarily less than 1/320 of an inch in diameter, so that the passage of all but the finest particles is prohibited. The bacteria would even pass through here, were it not for a second service of sand, which acts in a most remarkable way as a support for a true bacterial filter. As the affluent passes through the upper layers, the sand stops the coarser materials left in the liquid and held in suspension there. Soon there forms above the original surface a filter composed of the smaller sediments, a layer so fine that even the infinitely small microörganisms cannot pass. Here is a fortress placed across the pathway of the invading germ, a barrier so effectual that water has been taken from sources frightfully polluted with typhoid or cholera germs, and has been safely furnished to thousands from the same source of supply.

The sediment filter is, of course, constantly increasing in thickness, and as it increases more and more pressure is necessary to drive water through the interstices. When the point is reached where the pressure required to force the water through is too great to be practicable, the surface of the filter is scraped. Since during this scraping the filter has to be out of commission, filter plants are generally built up from a series of small filters, in order that one or more may be out of use at any time for repairs. Filters may be either open or roofed, the covering of the filter beds depending upon the question of geographical location. The North requires covered filters, while the South gets along very well with open ones, the chief difficulty being due to ice formation.

Besides the continuous filter described above, only one form of filtration is commonly employed to-day, — the mechanical filter. For the last ten years the growth in number of plants of this type has been most remarkable. The mechanical filter differs greatly from the continuous filter. It delivers from fifty to one hundred times the quantity of water, and is correspondingly reduced in size. A single continuous filter may occupy an acre, while half a dozen mechanical filters may be installed in less than a quarter of that space. The former filter recognizes as a cardinal principle the keeping intact of the surface of the filter where the bacterial life is strained out in the close upper layers. The latter accomplishes its work by the addition of a chemical, whose action on meeting the water is such as to engulf all matters held in suspension, including bacteria, thus forming comparatively large masses, which can be filtered without difficulty. The chemical commonly employed in the mechanical filter is sulphate of alumina, which, when added to water, separates into sulphuric acid and alumina, the latter being a flocculent cloudy precipitate which spreads out over the water. The heavy precipitate thus formed settles down upon the sand, and, acting like a sediment layer in the continuous filter, removes the germs. As with these large masses the clogging tends to stop the flow, the sand at brief periods is washed and stirred, with removal of the former residues.

Now as to household filters. What can we do in the private home to stop the entrance of the disease germ, provided we believe danger exists ? The sanitary experts say that no small filter which allows a good stream of water to pass removes bacteria. In the sale of such filters and the belief in their efficiency lies peril to the public, who so often believe that a couple of inches of sand or charcoal preserves them from all harm. As a matter of fact, expert engineers are practically agreed that eighteen inches of sand above drains, and that well covered with the sediment filter, are necessary to obtain efficiency. Some of the larger household filters are efficient when filled with fine filtering matters, such as sandstone and infusorial earth, which only allow water to pass drop by drop. These are usually either provided with storage reservoirs, or joined in a series of filters so that a quantity may be obtained at once despite the slow rate of filtration. One simple safeguard is always at hand, and should never be forgotten, — the boiling of the drinking water. No precaution is better in time of epidemics. One point should be made clear, — individual protection can never possess a fraction of the value that belongs to municipal control, any more than the individual extinguisher can compete with the city fire department.

The teeming thousands in the narrow ways receive one common food, the city water. We have already considered the way in which it may be delivered to all, pure and free from dangerous burdens. We must now consider the other side, the outgo of the city. Every organism as a condition of its existence must be forever building up and breaking down. Life depends upon the proper balance of the constructive and destructive forces of nature. From the decomposition of the organic foods and various materials used in our complex life, from the sweepings of the streets and the discharges from factories and shops, comes the outgo of the city, its sewage.

The sewer is the abiding-place of good and bad bacteria, five million or more of which may make their home in a single cubic centimetre. In the sewer they find darkness, moisture, and food; and there they thrive and multiply. Far more important than the number of evil microorganisms found there is the certainty of the presence of deleterious organic matters which, in their present state, and in their changed form after decomposition, are products dangerous in themselves and noxious to all around. We have hitherto considered chiefly the removal of bacteria of disease; but we must here consider as of primary importance the elimination of the harmful elements of the city wastes.

The realization that sewage, unless properly purified, might be a danger to the community is a matter of comparatively recent growth. In 1815 London used her sewers only for rain water, and disposition of other matters therein was forbidden. Here and there in isolated cases might be found early attempts at some method of disposal, as in the case of the little town of Bunzlau in Prussia, which in 1559 had a piped water supply and a system of sewage farming. These attempts at scientific solution of the problem were at best sporadic until the year 1844, which marks the opening of an era that recognized the necessity for proper waste disposal. This era began with the remarkable “Report of the Health of Towns Commission in Great Britain,” which for the first time revealed the dangers which might come from improper waste disposal and the accumulation of sewage. As a result of that report arose the “Filth Theory of Disease,” which, since it is not yet eradicated from the popular mind, and since under it was accomplished some of the best sanitary work of the century, needs at least a passing mention here. According to this belief, disease was bred in masses of decomposing filth; it originated there, and was in some way a product of the reactions therein contained. We now know that the main part of this theory is false, and that disease cannot originate in filth, although it does find there a convenient carrier.

This “ Filth Theory of Disease” swept through the scientific world with the most surprising rapidity. The problem of sewage disposal became urgent in a moment, and soon the modern method of sewage carriage, dilution with water, was evolved ; and the problem became that of handling a mass of wastes enormously diluted with water, a dilution so great that in America there exists but one part of solid in one thousand of water. Disposal by dilution is in some special cases possible. It is true that where not more than one part of sewage is sent into fifty of water, the oxygen of the water may be sufficient to take care of the wastes; but this proportion of water to sewage is so large that, save on the sea, on great lakes, or on rivers the size of the Mississippi, any such disposal is unsafe in the extreme, and any use of water from such a source must be a constant danger.

The first step in any handling of sewage is such a separation of the wastes that the different parts may be handled to the best advantage. The first treatment consists in screening the large floating objects which have entered the sewer in various ways, and removing all rags, bits of wood, and the like, which may be in the liquid. There will still remain in suspension a large amount of gravel and other matters of that type, which have been washed in from the sewer openings in the streets. This may be removed by checking the rate of flow, and so allowing a settling-out to take place. That leaves as the crux of the problem the disposition of the organic matter which is left. Purification by chemical preeipitants, such as are used in the purification of water in mechanical filters, has been tried in the past and has proved unsatisfactory.

Before passing to the consideration of particular details, let us turn for a moment to consider by what method this cleansing may be brought about. Sewage must either putrefy or nitrify. That is, it must either decompose (with results unfavorable in the extreme), or such chemical action must take place as will change the harmful organic ingredients to harmless inorganic matters, a result really effected through bringing them somehow into contact with the air, the oxygen of which will consume them. These organic city wastes, while most complex, and differing greatly in their individual structure, are yet composed chiefly of but four elements, carbon, hydrogen, nitrogen, and oxygen. The oxidation or nitrification of such wastes consists in so combining the nitrogen with the free oxygen of the air as to form nitrates. This is the most essential reaction, though at the same time the hydrogen is oxidized to water, and the carbon to carbon dioxide.

The problem before us, then, really resolves itself into this: How may we so oxidize or nitrify sewage as to change the noxious organic matter into harmless mineral substances? To do this the sanitary engineer reverses his processes. Instead of removing the germs, as in water filtration, he cultivates myriads of helpful bacteria. Whether we consider such sewage disposal as carried on by natural or by artificial means, on the irrigated farm or the trickling filter, we find this startling and remarkable fact, — the oxidizing of the sewage is done by millions of living organisms. These bacilli take in the organic wastes and turn them into safe and harmless inorganic matters. To cultivate such bacteria, and to use their destructive powers on dangerous elements, has been the effort of all recent sewage researches. How they are accomplishing this task may be told briefly here.

The oldest form of sewage disposal is the disposal on land for use as a fertilizer. For more than four centuries the sewage farm has been an attractive conception to students of possible economies of the state. Berlin and Paris have both had farms of this kind for years, and many other experiments along this line have been made here and abroad.

On soils even moderately fertile the sewage farm scarcely ever pays, costing, despite returns, more for its maintenance than other types of disposal systems. It is on soils like those of the West, where the water carrying the organic matter is of value for irrigation, that sewage farming has been made to pay, and there is every reason to believe that in such a region it could be made a most profitable municipal investment.

The fertility of any soil is greatly affected by the bacterial action which goes on in its upper layers. The bacilli on the soil of sewage farms are the oxidizing agents, taking in the organic, and sending forth inorganic, matters at the end of the reaction. As the fertility of the soil increases, the effectiveness of the plant to nitrify the sewage increases as well; but two precautions must be taken in any use of sewage for fertilizer. No crop should be raised which is to be eaten raw, and preferably no crop intended for human consumption. Secondly, no crop should be employed which covers the soil too closely, as does alfalfa, for instance. A notable example of successful Western sewage farming is shown by Pasadena, California, where walnuts, a crop safe from bacterial infection because of their shell, and free from all clogging of the porous soil, have been grown with profitable results. A substantial profit has been made year by year, and from the surplus the original cost of the land is rapidly being paid off.

Leaving this natural process, we come to the processes evolved by science. By 1865 it was recognized that the essential factor in the purification of sewage by means of land was the bacterial action upon the organic wastes. Early investigators had some inkling of the fact, and had proposed a system by which, through the special cultivation of the destructive germs, a rapid purification might take place. By passing the organic wastes of a community, with their accompanying microörganisms, through great masses of destructive bacteria of the proper type, these waste products might be broken down, the living organisms destroyed,and the harmful elements removed. A tremendous conception, this enlisting of armies of good bacilli to fight the hosts of evil! This theory has directed the scientific attack on the problem for the last thirty years. Given the possibility of such action, what method could best carry it out?

In 1887 conditions in Massachusetts had become so serious that there was instituted by the State Board of Health an experiment station at Lawrence for the study of sewage disposal and water supply. It was put under the charge of Mr. H. F. Mills, with the coöperation of Professors Sedgwick and Drown of the Massachusetts Institute of Technology. At that station were carried out the classic Lawrence experiments.

In these researches ten different filtering materials, such as gravel, sand, loam, and the like, were placed in ten experimental tanks, and the same sewage was passed through each. Continuous and intermittent filtration was tried, and the number of bacteria present before and after filtration was most carefully determined. As a result, the great principle was established that purification is an oxidizing process carried out by bacteria living in the filter, and (a most important result) that a rich supply of oxygen was necessary for their activity. The process of action with oxygen is known as the “breathing of the filters.” It was early found that in sewage filters, like the continuous water filters, there was not sufficient opportunity for the bacilli to obtain enough oxygen to oxidize the organic matter passing over. In consequence it soon became evident that maximum efficiency would be obtained only when — the filters having been once filled with sewage “the bacteria should be allowed to act upon it with free access to the oxygen of the air. This intermittent action, the addition of the sewage followed by the addition of supplies of oxygen, is a battle in which the foe is met by a defending army whose ammunition is constantly renewed.

The principle of the intermittent filter is found in the other modern devices by which bacteria meet bacteria in deadly battle. The contact-bed system, used advantageously in England, is found but rarely here. In this system, the liquid, instead of passing through the filter of sand, is let into a great tank filled with coke or some hard, smooth material; this is then filled with sewage and closed. The sewage is allowed to remain there for two hours or more. During this time the bacterial films upon the rocks absorb the organic matter and bacteria present, and at the end the remaining liquid is discharged. Oxygen is thereby allowed entrance to the films, and the bacteria do their appointed work as scavengers. By careful regulation as to the time necessary to accomplish the results, satisfactory purification may be obtained; but extreme care has to be taken in the control.

The third type of disposal is still simpler in principle. In early experiments with intermittent filtration, air was forced in from below to allow for the breathing of the filters. Soon the necessity for more air, for increased supplies of oxygen, made further experiments along the line of intermittent filtration necessary. In the trickling or sprinkling filter it was first made possible to treat sewage with a continuous supply of air. In this process, by one means or another, — the tipping of small buckets or splashing from sprinklers,—the sewage is constantly passing into a filter filled with coarse gravel. As it trickles down between the openings, it carries with it air for its own destruction. Oxygen is also obtained from the open construction of the filter, which allows constant air communication between the interstices. The bacterial films upon the stones absorb the organic matters and new bacterial life, as in the case of the contact bed; and through the constant breathing of the filters the oxygen necessary for the burning up or oxidization of the wastes is secured.

To produce complete bacterial efficiency the effluent, or outcoming liquid, may be rapidly filtered through a second filter, filled with sand or sterilized by copper.

The action of the intermittent filter and the possibilities of its use can be expressed in no way better than by quoting the brilliant ending of Mr. Winslow’s article on this subject: “The trickling bed appears to be the ideal method of solving the essential problem of sewage disposal, the oxidation of organic matter. It exhibits the simplicity of all scientific applications which are merely intelligent intensifications of natural processes. A pile of stones on which bacterial growth may gather and a regulated supply of sewage are the only desiderata. We meet the conditions resulting from an abnormal aggregation of human life in the city by setting up a second city of microbes. The dangerous organic waste material produced in the city of human habitations is carried out to the city of microbes on their hills of rock, and we rely on them to turn it over into a harmless mineral form.”

One last method of bacterial destruction of sewage must be considered here, — the septic tank, the successor of the individual cesspool. While impracticable for final disposition, it has an unquestioned value as a preliminary step in the treatment of certain concentrated sewages. The principle of the ordinary cesspool depends upon the fact that a large part of the solid organic wastes are acted upon in the closed dark receptacles, without access of air, by bacterial ferments, and are turned into a liquid which may be drained off. Such solid portions as are unaffected by this change may be removed a couple of times a year. In the modern form of septic tank the wastes, instead of being left to be acted on for a long period without the use of oxygen, are run into a close tank where they are left for about twenty-four hours. During this time, the chief decomposition has taken place, after which the residues are pumped to the filters or contact beds, where the final oxidation may occur by means of the oxygen of the air.

We have already considered the use of the household filter in some detail; but the general problem of good water and safe sewage appeals to every owner of a country house, and a few words on this subject should be inserted here. The best soil for these purposes is a sandy one, and wherever a rocky or clayey soil gives possibility of a fissure which might connect water and drainage, expert examination should be called in. The individual plant for sewage disposal may often be a well and a cesspool, — the cesspool, once a bogy to sanitarians, being now justified by the septic tank and the sand filter, both of which principles are employed in its construction. Two points must be recognized here. Such a covering of the well that the grave danger of surface pollution may be avoided, for it is most essential that no pollution should be washed through covering boards. Also the direction of drainage, which is generally toward the nearest water course, must be such that the water supply may not be below the point of sewage disposal. With these simple precautions of soil, covering of well, and proper location of water and drainage, the isolated country house owner may feel secure.

Lastly, to sum it all up: what is the present status of the work ? What is the real purpose of sanitary engineering, and how does it affect us as public-spirited citizens ?

As we look over the whole field of effort, the striking factors of present-day progress in bacterial removal and sewage disposal seem to be taking on definite specialized form. The sanitary engineer is using one method for water, — the removal of evil bacteria by filtration. A very different method prevails to-day for sewage, — the cultivation of good bacteria which may render safe the city by their removal of its dangerous organic wastes. Removal of the evil and cultivation of the good! The most highly specialized forms of water and sewage filters show this best. The mechanical water filter has chemicals to separate out the bacteria, pneumatic arrangements to wash out the sand, and casings of concrete for protection from the air. The sewage filter, on the other hand, is, in its essentials, nothing more than a pile of rock on which the good bacteria may grow. The future advance of sanitary science seems likely to be along these lines. More and more dependence is placed upon research, and the real importance of the problem seems daily more manifest. The careful experiments at the Columbus Experiment Station in Ohio, as well as the fact that a Sewage Research Station has been established by the Massachusetts Institute of Technology, show the trend of the day.

To make the city habitable, to increase the efficiency of the state through the better health of its citizens, — what task is higher than this great labor for the common good ? On the man in control of the water system or the sewage plant rests the success or failure of many measures planned for the public weal. In the solution of that great problem in applied science, the government of the city, no man must bear a greater responsibility than the sanitary engineer. In such solution research and study may do much; but all individual effort must be supported by a righteous public sentiment. Such civic interest should be awakened in every community as will demand that the guardians of our public health shall be rightly trained, wise, and free. Above all free, — since freedom from political control, from jealousies and narrowness, must be secured in order that full power may be given to the guardians of the public health to keep up the fight until the final conquest of the germ.