AERATION OF WATER SUPPLIES BY NATURAL CANALS AND LOW DAMS
The ideal drink of water is out of “ the old oaken bucket that hung in the well.” Remove the old bucket with its balance beam 3nd substitute a modern pump, the ideal drink vanishes, the water seems insipid, the charm has left the well, we wish the old bucket back, lay it all to the new fangled notion of a pump; yet we stop there and fail to inquire the true cause. The charm lies neither in the old oaken bucket nor in the pump, but is due, pure and simple, to aeration. The bottom of the old bucket was about one inch above the chime of the staves. Every time the old bucket was sent down into the well it carried with it a quantity of air, measured by the area of bucket bottom multiplied by the depth that the bottom of bucket was inserted in the staves. The pump, owing to its mechanical construction, carried no air down into the well. Further comment seems unnecessary.
Again, on a larger scale : The mountain brook, rumbling along its rocky bottom, here a little cascade, there a pond, now coursing along a run of water-worn stones and boulders, again a waterfall, and so on for perhaps miles, yet always pure, sparkling and palatable to the tired fisherman ! This is the ideal water supply—and why? Aeration and subsidence is the answer. What is aeration ? Webster defines it, “ to supply with common air.”
Water is composed of oxygen and hydrogen, and is uniformly in the proportion of 100 parts of oxygen to 12)^ of hydrogen by weight. Common air is formed of oxygen and nitrogen in the proportion of 77 parts of nitrogen and 23 parts of oxygen (Silliman) by weight.
Air is a mechanical mixture. The oxygen of the air is abstracted by all substances having an affinity for it, with the same ease as if nitrogen was not present. A chemical combination of oxygen and nitrogen forms nitric acid. The proportions then are four measures of nitrogen to ten measures of oxygen, while in common air the proportions are four measures of nitrogen to one of oxygen (Stockhatdt).
This is a striking example of how wonderfully the properties of bodies change when they chemically combine with each other. When mechanically mixed together the constituents of nitric acid form a life-sustaining gas, while when chemically combined they form one of the most corrosive fluids.
Oxygen has the greatest range of affinity of any known substance. Oxygen is absolutely necessary to all living creatures. Every combustion, however familiar to us, is a process of oxidation, in which the oxygen of the air combines with the particles of the burning material.
Oxygen, hydrogen, nitrogen and carbon are the four elements which the Creator has established as the basis upon which the whole structure of organic creation rests ; and from their combination with inorganic matter all the various forms of animals and vegetation proceed ; yet the inorganic matter bears a very small proportion to the whole. .Take an oak tree. Out of every 100 pounds only two to four pounds are inorganic, or ashes, and about the same proportion holds true of the animal kingdom. Oxygen seems to be the agent by which the changes in organic nature arc brought about. There is no chemical change in organic nature without heat. Heat is the outward evidence of combustion, and, as combustion is a process of oxidation, it follows that the changes of organic nature are substantially produced by oxygen as the agent. All animate nature is constantly undergoing a change. There is no stand-still. All animal and vegetable living matter of to-day will, in the course of a short time, be again resolved into the four elements, together with the different inorganic matters of which they are composed. And so the ceaseless change goes on, as it has gone on for centuries. Oxygen has been the principal active agent through all this, all tending to purity again. Were there not some such simple, yet universal and powerful agent constantly at
work, the earth would have been uninhabitable centuries ago, due to the fouling of the water supply, if from no other cause. Must it not then be true that water purification is due primarily to oxidation ; and, if we try to imitate nature closely, will not our success be measured by the nearness with which we approach with our imitation ? Is not nature’s process of oxidation, by using the oxygen of the common air, the most available agent ? Common air is tr.e most abundant form of matter in and about the earth. Does not the oxygen of the air combine with the impurities, form new chemical combinations, the force of gravity precipitate them, and are they not thus removed and the foul water made wholesome ? Is not this the true explanation of the purity and wholesomeness of the rock-bound mountain brook ?
PROPORTION OF AIR WATER WILL ABSORB.
Regnault, the French chemist, gives the proportion of oxygen which water will absorb. He says :
“ At the ordinarj’ temperature water dissolves about 46-100 ol its volume, or, in other words, one litre of water dissolves forty-six cubic centimetres of oxygen, or 100 cubic inches of water will dissolve 4.6 cubic inches of oxygen.”
Wanklyn, the well-known English water analyst, also gives the possible proportion of air which water will take up. He says :
“ Water is capable of absorbing, in a greater or less degree, every gas and every vapor which is placed in contact with it.
“All water which has been kept in open vessels is necessarily charged with oxygen and nitrogen gases, inasmuch as these gases form the chief constituents of the atmosphere ; and if any sample of water be freely shaken up with large volumes of air, it will presently become charged with nitrogen and oxygen in certain well ascertained proportions, dependent on a physical law.
“A litre of water freely shaken up with large volumes of air at fifteen degrees Cent, will absorb 17.95 cubic centimeters of air, the composition of which is :
“ The composition of the dissolved air is governed by the relative proportions of nitrogen and oxygen gases in the atmosphere, and by the coefficient of absorption of each gas at the temperature at which the absorption takes place. At fifteen Cent, (according to Bunsen) the absorption coefficient of nitrogen is 0.0148, and that of oxygen 0.0299, while the relative volume of oxygen and nitrogen in air are :
“The relative proportions of nitrogen and oxygen, which water dissolves from the atmosphere at fifteen degrees Cent, arc therefore, according to the law, 0.0148 x 79, 0.0299 x 71, which gives in percentages nitrogen, 65.1 volumes; oxygen, 34.9 volumes; total, 100.
“If water be taken from rivers and springs and be bottled up without being freely exposed to the air, it will often be found to exhibit a very different ratio between the dissolved nitrogen and oxygen gases.
“Thus in the autumn of 1859, W. A. Miller found that a litre of Thames water at Woolwich contained 63.05 C. C. of dissolved gases, the composition of these gases being :
showing extraordinary diminution of oxygen.
** Higher up the river the ratio of nitrogen to oxygen was quite different. Thus at Kingston Miller found in a litre of Thames water, 52.7 C. C. of gas;s, consisting of:
As will be observed, the ratio of the nitrogen to the oxygen in this water is very nearly that which they require in a perfectly aerated water.
** Undoubtedly the Thames water taken out of the river at Woolwich owes its deficiency of oxygen to the reducing action of urea and other
matters poured into the river in the form of sewage.”
Again I find that in a paper read before your association at Manchester, in June, 1SS7, Chas. Brush, C. E., of Hoboken, N. J., says:
“ It is absolutely essential to good water that there shall exist in it a certain equilibrium of animal and vegetable life, in order to produce and regulate the quantity and quality of gases essential to maintaining it in good condition. Prominent among these gases is oxygen—not the oxygen of which the water is actually composed, but rather additional oxygen in solution in the water, which varies greatly under different conditions. With an excess of oxygen in solution, stagnant water is never found. Filtered waters, or, what is practically the same thing, waters obtained from subterranean sources of supply, such as galleries or deep closed wells, after passing through natural filter beds, are generally bright, clear and quite palatab’e. If allowed to stand any length of time, however, in an open reservoir, such water soon deteriorates.”
The philosophy of this probably is, that the absorption of oxygen from the air again causes new chemical changes to occur, the composition of the water is changed, and for the worse probably. If left a great length of time the new combination would throw down precipitates, and the water would be essentially changed in its chemical constituents.
Again Mr. Brush says :
“The best supply is always obtained from water in motion. All waters, and especially those obtained from the surface streams, are better at some seasons of the year than at other seasons, and these seasons differ with the different sources of supply. Generally, however, the worst season with any is cither in mid-winter or in mid-summer. In the former case, when the streams are frozen over, the air is no longer in contact with the water, and consequently the water lacks life. In the heat of summer, especially after luxuriant vegetation, theoxygen in solution in the water seems to be used up to a greater or less extent, and there is an excess of vegetable life. In both cases the result is a fishy taste and smell, and algrr likely to develop.”
ROYAL COMMISSION ON OXIDATION.
The English royal commission on water supply (i860) in their report say :
“ If the waters of the Thames had no impurities beyond the solid mineral contents, the question as to their wholesomeness and general suitability for the supply of the metropolis (London) would be easily disposed of.
“ But attention has been called strongly to the organic impurities contained in Thames water, which, though more indistinct in their form and less appreciable in their quantity, are said to be more deleterious in their nature and to render the water, if not dangerous and unwholesome, at least liable to suspicion. The organic compounds dissolved in the water appear to be of very unstable constitution and to be very easily decomposed, the great agent in this decomposition being oxygen, and the process being considerably hastened by the motion of the water.
“ Now, as such waters contain naturally much air dissolved in them, the decomposing agent is ready at hand to exert its influence the moment the matter is received into the water, in addition to which the motion causes a further action by exposure to the atmosphere, and when (as in the Thames) the water falls frequently over weirs, passes through locks, etc., causing further agitation and aeration, the process must go on more speedily and more effectually. The effect of the action of oxygen on these organic matters, when complete, is to break them up, to destroy all their peculiar organic constitution, and to rearrange their elements into permanent inorganic forms, innocuous and free from deleterious quality.”
Alum is the substance now almost universally used in the patent filters of the present day, yet an examination into its chemical constituents would seem to show that its efficiency is due to the large proportion of oxygen that goes to make it up. Its chemical symbol isAI»Oi, 3SO*-f-KO, SO* + 24HO, which, being reduced to its elements, indicates that 27.38 parts of the earthy metal aluminium, 64 parts of sulphur, 39.19 parts of potassium, 24 parts of hydrogen and 320 parts of oxygen, make up the whole.
HUMBER ON OXIDATION.
Humber in his work on water supply says :
“ Oxidation is another process carried on by nature for the purification of fouled water. It operates upon the class of impurities which, with one exception, are most to be feared, viz.: organic matters liable to decomposition or already partially decomposed. The oxygen which is always dissolved in water exposed to the air, and the free atmospheric oxygen with which the organic matter is brought into contact by the motion of the water, combine with that organic matter, thereby converting it into harmless nitrates, nitrites and carbonic acid. The more v’olent the agitation and more complete the aeration of the water, the more thoroughly will the organic matter be broken up and changed into these innocuous inorganic forms. The purifying agent is always at hand and in superabundance ; it is only necessary to utilize it by bringing it into contact with the substances upon which it has to act.”
* A papier read before the New England Water-works Association at Providence, R. I., June 14, 1888, by Stephen E. Babcock, civil and hydraulic engineer ; member of the New England Water-works Association: chief engineer Little Falls Water-works. Little Falls, N. Y.
The concurrent testimony of all who have looked up the question of water impurities and their removal seems to be that a violent mixing of common air with water is the most effectual and natural remedy.
AERATION AT LITTLE FALLS, N. Y.
At Little Falls, N. Y,, where I am now’ engaged in constructing a water-works system, the source of supply is an exceptionally pure mountain brook of three to four million gallons daily run. It is the finest trout brook in the whole section around Little Falls, yet, as I bring the water eight and three-quarters miles through an inclosed conduit, I concluded to try and imitate nature’s process of improving it, and with what success the following description will enable )ou to judge :
The closed conduit terminates at a point about 2500 feet from the distribution reservoir. From here to the distribution reservoir I constructed an open, paved channel to near the distribution reservoir. The object of this open channel is to aerate the water by causing the same to pass over a scries of sixteen weirs, ten feet long, two feet high, distributed along the open channel at intervals of fifty and 100 feet apart, as the contour of ground admits. The paved channel begins at end of conduit, starting with a retaining wall, and is three feet wide on the bottom, five lect from top of bank down to grade, three feet nine inches of which is excavation in natural soil. The excavation is utilized to form towpath and berme banks, six feet wide, on each siil0 of open channel throughout the whole length of the same, preventing any surface drainage from entering the canal. The open channel is carried 390 feet to a ravine or depression in surface of the ground ; here a retaining wall is built up to top banks and two feet above the natural surface of the ground ; the water is then carried in a pipe 160 feet through under the surface of the ravine. At the outlet another retaining wall is built up to top bank and two feet above the natural ground. Open channel starts again and is carried along for 580 feet to another ravine roo feet long, where the water is again carried under through pipes and protected bv vertical walls at each end, and with weirs or dams placed fifty and 100 feet apart, of the same size and dimensions as first stated. The water is again carried 700 feet in open channel to a point near the line of by-wash canal, which carries the water of the several streams formerly running through the reservoir past, without entering the reservoir inclosure. From this point the water is conveyed in an iron pipe. 970 feet, to and through the bed of the distribution reservoir to a point out in the centre of the same, distant about 430 feet from the gate house and too feel from the sides of reservoir ; here the pipe is turned up vertically and held in place by a rectangular mound of masonry, which is carried up two feet above water surface of the reservoir. The water is allowed to fall over the sides of a square copirg on top of mound, giving a final oxidation to the water as it mingles with the waters of the reservoir.
The total oxidation of the water after it has been confined in eight and tluee-quaftcr milt s of conduit is represented by the aeration over sixteen weirs or dams, ten feet wide, two feet high, a total length of open channel 1600 leet, with a final overfall in the centre of the reservoir, removing all possibility of fouling the water by surface wash on edgeot reservoir. Aga n, by passing the water through pipes under the two ravines, ail the surface warm and drainage from the end of conduit to the diverting or by-wash canal is carried on the sutface of the ground through these ravines, and cannot contaminate the water in open canal.
Near the point where the iron pipe from last section of aerating canal passes under the diverting or by-wash canal I placed a branch with a pipe leading into by-wash canal, locating valves on two ends of the branch. The aerating canal forms also a series of subsiding ponds or reservoirs, and to provide for a ready means of cleaning them I placed the above mentioned branch controlled with its valves. Whenever the canal ponds become filled with precipitated matters the line leading to the distribution reservoir may be closed, the one leading to the bywash canal opened ; this allows all the water to waste into the by-wash canal. To clean the ponds and canal, it is only necessary to stir up the deposits with brooms or other suitable tools, and the water carries them along down and out through the by-wash canal to waste, until such time as the canal has been cleaned and water runs clear, when by changing the valves the pure water may again be sent into the reservoir. The water is kept in a constant state of agitation with the air from the time it strikes the first dam to the end of the aerating canal. This I claim to be a fairly close imitation of nature’s own way of rendering water pure and wholesome as well as pleasant and palatable.
Yet there is one item in water purification also to be looked into, the exception referred to by Humber. That it is a disputed point as yet as to how far aeration goes in removing the living germs seems to be the fact. Humber says :
“ The class of impurities of which exception was made as being that most to be feared is, unfortunately, the class upon which the action of simple oxygen is of the most doubtful efficiency. The microscopic organisms known as germs would seem to defy the action of oxygen by that very element of vitality which renders them so persistently dangerous. While, however, the opinions of scientific men on this point are still so conflicting, it would be unwise here to do more than recommend the strictest cau’ion.”
I determined to obviate this possible danger by adding a coke filter in the inlet chamber of the distribution reservoir. The particular description of inlet chamber and filter is as follows: The inlet chamber is of rubble masonry divided into three compartments. The first compartment nearest the water is arranged with two sets of screens running from top to bottom of house ; three inlet tubes are placed on the inner side of this chamber, governed by regulating valves ; these inlet tubes are placed at different elevations below the surface. Water may be drawn from either one as may be required. The water then passes into the middle chamber, which is a coke filter bed. The coke extends down from the top to a rack placed five feet above the bottom of the chamber. From this chamber the water is drawn into the third chamber by another inlet tube placed two feet above bottom and below the coke. From the third chamber two pipes lead the water down to the distribution system. A twelve-inch mud pipe is also provided, laid through from the front chamber to the outer line of the embankment.
Provision is made to clean the filter from time to time as may be required without interfering with the supply to the distribution, as follows: A short twelve-inch inlet cleaning tube is led from near the bottom of the outer chamber to a point directly under the centre of base of the coke. A twelve-inch waste pipe connecting by branch with the mud pipe is let in from top of coke in middle chamber down to mud pipe in third chamber. Two additional supply pipes are Carried through from chamber No. 1 to chamber No. 3, to use to supply the distribution while the coke is being cleaned.
When the filter is to be cleaned the regular filter inlet tube is closed up. The additional supply pipe leading past filter is opened, supplying the distribution independently of filter bed. The short twelve-inch inlet cleaning tube is opened ; the water then passes up through the coke, reversing the line of flow, thus freeing the coke from all ihe deposits, and the foul water is passed off through the twelve-inch waste pipe that leads from the top of the coke down to the mud pipe and thence out to the ground at the foot of slope of bank. Tfte coke may thus be cleaned as often as it is found necessary. I adopted coke as a filter material from its very favorable action on the microscopic living germs.
Mr. Percy Frankland, the well known English analyst, has made some very exhaustive experiments to determine the relative values of coke, animal charcoal, and other substances. (Proceedings of Institute of Civil Engineers, England, 1886.) He says:
Until the method of water examination by gelatine culture was devised, there were no available means by which the relative efficiency for the removal of micro-organisms of different filtering material could be estimated on a quantitative basis. The author has* submitted to examination, as regards their efficiency in this respect, a number of filtering materials, employing in all cases equal thicknesses of the various substances which were also prepared in the same state of division. The results obtained in these experiments were :
“ Ferruginous green sand. Initial efficiency organisms per cubic centimetre, before filtering, 80 ; after, none. Reduction, per cent 100. After thirteen days, before filtering, 8000; after, 1000. Reduction, per cent 88. After one month’s action, before filtering, 12S0; after, 780. Reduction, per cent 39.
“Animal charcoal. Initial efficiency, organisms too numerous to count before filtering ; after, none. Reduction, 100 per cent. After thirteen day’s action, before filtering, 2800; after, none. Reduction, per cent too. After one month’s action, organisms before filtering, 1280; after, 7000. Reduction none, but an increase of 447 per cent.
“ Coke. Initial efficiency, organisms per cubic centimetre before filtering, 3000; after, none. Reduction, per cent 100. After five weeks’ action, before filtering, 6000 ; after, 90. Reduction, per cent 98
“ The author has made further experiments on the efficiency of coke as a filtering material. In these experiments the filters employed were of similar construction, but an aqueous extract of garden soil was employed instead of urine water. Two similar filters (a) and (b) were submitted to examination under conditions as similar as possible.
INITIAL EFFICIENCY (SECOND DAY).
Unfiltered water, 26,030organisms per cubic centimetre: Filter (a) none.
Filter (b) none.
Reduction in both, 100 per cent.
After three weeks’ action, twenty-first day:
Unfiltered water, 2230 organisms.
Filter (a) 339
Filter (b) 219 “
Reduction (a) 85 per cent; (b) 90 per cent.”
Mr. Frankland’s experiments show that with the coke filter properly attended to, it may be relied upon to do the work expected.
I am satisfied that this system of water purification by aeration, using water-ways or canals and a series of low dams, may be adapted to both gravity and pumping systems, and form a permanent, cheap and reliable method of improving the quality of potable water, and when once constructed it runs itself.