IOWA HISTORY PROJECT
MODERN CONVENIENCES FOR THE FARM HOME
DISPOSAL OF SEWAGE
After the plumbing has been put into the house, to make it effective, a means must be provided to remove all liquid wastes as soon as possible and to prevent the return of odors.
Dangers of a cesspool. - As has been previously explained, to build a cesspool to foul the ground and air is not a solution; it is only putting the trouble "out of sight." It holds the wastes in a state of putrefaction, and so will give off troublesome gases, which will, if near the house, penetrate to the cellar and then on through the house. Its liquid leachings, if these strike a layer of sand and gravel or a fissure in the rock, will penetrate an unthought-of distance to injure the quality of water of wells and springs. Such a system would never be installed if the householder realized the full effect of the nuisance he was establishing. Fortunately it is no longer necessary to build a cesspool when plumbing is introduced into the house which can not be connected to a public sewer.
Principle of modern sewage disposal. - Within the last twenty years many investigations of sanitary methods for the disposal of sewage for isolated houses have been made. The working principle is this: When the air contained in the soil is brought in contact with dead organic matter in a finely divided state, a complete transformation takes place by the natural processes of oxidation and nitrification. This change is brought about by micro-organisms which multiply rapidly under proper conditions and by so doing combine the oxygen of the air with the organic matter. Air is as necessary for this purpose as fuel in a stove that is required to give off heat. It is therefore essential that the waste be disposited on or near the surface of the ground and in such a way that air reaches every particle. If the ground is saturated for a long period of time purification of the liquid will cease. If a foul liquid is thrown on the surface of the ground the water will pass off, but its organic impurities will cling to the particles of earth. Air take the place of the water and surrounds the waste matter, the bacteria present in all fertile soils effect a combination between the two, converting the dead organic matter to harmless mineral forms needed for vegetable life. This process may be repeated indefinitely if the waste matter be supplied and the air furnished alternately. This is called the "intermittent method" of operating the disposal plant. The process of applying this principle to the disposal of sewage varies, and may be divided into two distinct steps: (1) The collection of the wastes from the house that these may be applied intermittently; and (2) their application to a natural soil by surface or subsurface irrigation, or to a specially prepared soil, as in a filter bed.
Three systems described. - The ground available on one farm can not be, and need not be, exactly the same as that used on another. If the surface is almost level and under cultivation the subsurface system of distribution could be adopted, whatever the method used for collecting the flow from the house. The liquids are retained for a certain length of time and then rapidly discharged into open-jointed tiles, laid near the surface, thus securing a uniform distribution throughout the entire length of the drain. While the tank is refilling thime enough is allowed for the water to pass away and the air to enter and accomplish its work. This manner of purifying the liquid wastes of the household where the water-closet is or is not used has been tried with entire satisfaction.
Another method of getting the liquid wastes on teh land is by surface irrigation. The most marked feature of the change from the privy to the water carriage system is the great dilution which the organic matter undergoes. Instead of concentrated organic wastes, unsuited for direct use as a fertilizer, we now have a dilute mixture which seldom contains more than 1 part of 500 of anything but water. Of course this can not be discharged in a haphazard manner upon the land, but if the intermittent method, as explained above, be followed and the discharge be regulated to avoid saturation of the ground, the sewage can be disposed of without unsightly or offensive results. The area of the ground required is about the same as for subsurface disposal. A slopping surface in grass, or partially wooded, or a cultivated field, say of corn, would be entirely suitable. The area required depends upon the character of the soil and the amount of sewage to be purified. For a family of five, if the soil be reasonably porous, a plat of ground 40 feet by 50 feet should be ample.
The third method of exposing the liquid wastes to the action of the bacteria is used when the available area of the land is limited or if on account of the character of the soil too large an amount of drains would be necessary to handle the sewage to be purified. Under these conditions specially prepared beds of sand, gravel, or screened cinders are used as a filter material. The sizes of these beds vary with the amount and character of the sewage and its previous treatment, but for a family of five under reasonable conditions and a proper preliminary treatment, a bed 25 feet long, 4 feet wide and 4 feet deep should answer, although one 5 feet deep would give a purer effluent.
COLLECTING THE LIQUID WASTES
As has been pointed out in the previous paragraphs, intermittent application is the key to success, and in order to apply the liquid waste or sewage to the land intermittently it is necessary to collect the irregular flow from the house in some manner.
The house drain or sewer. - The house drain of cast-iron pipe extends at least 5 feet outside of the foundation wall. From this point to the collecting chamber vitrified sewer pipe is used, except in made ground or in quicksand or where the drain must pass near a well, when cast-iron pipe should be provided. The drain should be given a uniform fall if possible, and should be at least 3 feet below the surface in cold climates, to avoid freezing. The greater the inclination the less the liability of obstruction. A fall of 1 foot in 40 or 1 foot in 60 feet is desirable; 1 foot in 100 feet is the least that should be used unless special flush tanks are provided. The bottom of the trench should be dug to the exact grade and shaped to fit the lower half of the pipe, with grooves cut for the sockets. Inspection and cleaning hand-holes should be located about every 50 feet, and their exact location marked on the plan of the drain, to aid in locating obstructions, if any should occur. Change of direction of the pipe line should be made with special curved pipes of large radius.
Making the joints. - The joints of the pipe should be well made. The space between spigot and hub should be filled first with a small rope of picked oakum, rammed into place with a hand iron to prevent any cement mortar from entering at the joints. Then fill the remainder of the space with a mortarmade of one part Portland cement and one part clean sand. The cement and sand must be thoroughly mixed dry and wetted up only as needed. The bottom of the joint should be made with particular care, using the fingers to press the mortar into place. As soon as the joint is finished the groove in the trench should be filled with earth to prevent the joint being broken before the cement has time to harden. The inside of the pipe must be thoroughly cleaned from projections of oakum or cement. If the drain passes close to trees the joints should be surrounded by concrete to protect the pipes from the roots of the trees. Before refilling the trench the joints should be tested by closing the main outlet and filling the pipes with water. Leaky joints are undesirable, both because of the contamination of the soil and because the liquid is needed to carry the solid matter through the pipes.
Volume of sewage. - The volume of the sewage is practically equal to the water consumption. The waste matter received increased the volume very little, 1 pound in 120 gallons is organic matter, to remove and destroy which is the purpose of the "disposal plant." The garbage or kitchen refuse of course is not included. This 1 pound of organic matter with its 120 gallons of water is all carried by the house sewer to a suitable place, the distance from the house varying with the surrounding conditions, and collected in a chamber to which has been given various names, according to the manner of use proposed. We have the "flush tank," the "settling chamber," and the "septic tank," and these may be so constructed and used that it is difficult to draw an exact line between them
A flush tank may be built of brick or of concrete, and is designed simply to collect the irregular house flow in order that it may be applied to the land at intervals varying from twelve to twenty-four hours. The size of such a tank depends upon the number of persons in the family using the water supply, which again varies with the habits of the family. The report of the data collected upon the use of water in the city of Columbus, Ohio, where 80 per cent of the houses are metered, states that the amount of water used per capital per day varies from 60 to 100 gallons.
A Simple Flush Tank
The simple flush tank is designed for a family of six, using 60 gallons of water each per day. If the flush tank is to empty in twenty-four hours, the tank must be designed so the siphon will empty it when 360 gallons of liquid matter are collected. Counting 231 cubic inches to the gallon, the capacity of the tank must be about 48 cubic feet. The depth at which the liquid will stand in the tank will be determined by the action of the siphon. The automatic siphon will hold the sewage to a depth of 1 foot and 3 inches. Whenever the tank fills to the discharging line the liquid is set in motion through the siphon, and when the tank is empty the siphon "breaks," and no further discharge takes place till the tank is full again. The depth of the sewage being fixed by siphon selected, in this example at 1 foot and 3 inches, the area of the tank must be 38 square feet to hold the estimated flow. A width of 4 feet and a length of 9 feet gives about the required capacity.
Construction. - This tank is built of concrete in the proportions of 1 part of Portland cement, 2 parts of clean sand, and 4 parts broken stone or gravel. If the sand contains both fine and coarse grains so much the better. The broken stone or gravel should vary in size from 1/4 inch to 2 inches in longest dimension, and the more variation within these limits the better.
Care should be taken to make the excavation just equal to the exterior measurements of the tank, in order to save material. Slope the bottom toward the outlet and cover it with 4 inches of concrete for the floor of the tank. Set the outlet while the floor is being laid. Build the interior form using wood screws in construction, as pounding to remove might injure the concrete. This framing is set on the floor when the cement has hardened. Inch boards are used to complete the form, and are put in place as the wall is carried up. The concrete is put in layers from 8 to 12 inches deep, and is thoroughly rammed with a 4-inch or 6-inch rammer, which weighs about 20 pounds. The inlet pipe must be set at its proper elevation. When the top of the uprights is reached segments of circles are supported on them. These have a rise of about 9 inches, and should be fastened to the uprights in such a way that they can be readily removed, and so that they will not interfere with the bearing of the top on the side walls. The boards placed on these must be narrower, say 6 inches, and the concrete must be mixed somewhat wet, as little tamping can be done, only enough to exclude the air. This arch should be at least 5 inches thick. The manhole can be built by using sheet-iron forms, made so they can be expanded or contracted in removing them. A 4-inch space between those should be sufficient. The manhole walls are carried up to the surface of the ground. After a few days the forms are removed and the interior is plastered with a mortar of one part cement to two parts clean sand. If the boards have been given a coating of soft soap they will be the more easily removed from the concrete walls. If at any time in building up the walls fresh concrete is to be deposited upon that which is already set the surface of the old work should be cleaned and wet and coated with a mortar made of one part cement and one part clean sand. This precaution should also be taken at the joining of the sides to the bottom of the tank. For a water-tight tank it is better to lay the walls without such joints. Where the side walls are to join the bottom of the tank the concrete should be roughened after being rammed for the floor, and a 1 to 1 mortar spread over this roughened surface when beginning to build the side walls.
The cost of the materials for the concrete in this tank will vary in different localities. If Portland cement is bought at 44 cents a bag, sand at $1.50 a cubic yard, and broken stone at $4 a cubic yard, and approximate estimate of the cost of the material would be $23.
Use of screens. -When a simple flush tank like this us used, paper and such coarse material should be screened out at the inlet. This is accomplished by having two baskets (16 by 16 by 16 inches) made of diamond-mesh wire cloth woven of No. 12 wire, one to the inch, with an opening near the top at one side to receive the inlet pipe. Hooks are provided on the side wall to hold the basket in place, and as the sewage passes through the paper any solid matter is retained. The second basket is used as an alternate when cleaning is necessary, which should be done once a week. A very small residue will be found in the basket, and this should be removed and spaded into the ground. The basket retains all material that would be unsightly if scattered over the surface of the ground or might obstruct the draintile in the case of subsurface disposal. A single-chambered flush tank is not advisable in most cases for subsurface irrigation. The raintile would need to be taken up and cleaned out more often than when a settling chamber is use.
Open tanks. - These tanks may be built of brick and plastered inside with cement mortar. If desired, they can be built near the surface of the ground and left open. In this case wire-cloth screens built in sections should be furnished to protect the contents against leaves and rubbish. If an open tank is desired, it would be well to build it not more than 2 to 3 feet wide and get the cubic contents necessary to contain the daily flow by increasing the length, as the narrow tank is desirable to prevent the screens from sagging. If the walls are occasionally swept down after the tank has discharged no odor should be noticed in the neighborhood, and its location near the house could be objected to only for esthetic reasons. A tank which is open will be more likely to freeze over on the surface. To prevent this frames covered with boards might take the place of the screens in winter. The danger from freezing is not great, as sewage is warm when it comes from the house.
For subsurface disposal it is necessary in most cases to provide a double-chambered tank, the first chamber to retain the solid matter and scum until they dissolve, and the second chamber to accumulate the liquid wastes and discharge them intermittently by means of a siphon.
Description. - One type of the doubled-chambered tank was designed to take the place of two overloaded cesspools, which were creating disagreeable odors. The amount of sewage to be disposed of daily was estimated from the amount of water used by the family of five, the war supply being distributed through the house from a 580-gallon tank in the attic, which is filled about every other day by means of a hot-air pump. The flush tank was designed to take care of 350 gallons, or 70 gallons per capital per day. The pipe connecting the settling chamber with the flush tank is arranged to draw the liquid from midway between the surface and bottom of the settling chamber, so as not to disturb the solids that have settled to the bottom of the tank or the scum that floats on top. All sewage coming from the house passes into the settling chamber, where the solid matter to a greater or less extent is deposited. Owing to the character of the sewage, the decomposition of the solids is so active as to prevent any serious accumulation in the bottom of the settling chamber. It is necessary to inspect the chamber from time to time, and if undissolved solids accumulate to have them removed, probably about once a year. This accumulation when removed should be carried to the field and spaded into the soil at once.
Construction and cost. - This tank was built of concrete in a manner very similar to that previously described for the single-chambered tank. The manholes were built of brick, and the siphon placed directly under one of them for convenient access to it. The cost of the material for this tank, including the siphon and cast-iron manhold covers, was $51.61. The lumber for the forms cost $9.85.
An inexpensive collecting chamber designed by Prof. Anson Marston, of the Iowa State College, is a septic tank that is arched over with brick and only the two manhole covers appear on the surface of the ground. The screen of fine pebbles and of sand retains all solid matter in the septic chamber, and on account of the upward action of the sewage the screen does not become clogged. The siphon chamber will vary in size, depending upon whether a sand filter or subsurface irrigation is used for the second step in the purification of the sewage. With a sand filter the siphon chamber could be emptied in eight hours; with subsurface irrigation, in eighteen to twenty-four hours.
It has already been explained that only the upper layer of the earth contains air enough to allow of the bacterial action necessary for sewage purification, and also that nature has her limits and must not be overworked; hence, there must bean intermittent application of the sewage or the process of purification will cease altogether. Although the sanitary results would be accomplished by surface irrigation the character of the soil may allow and the requirements of the family demand the distribution to be beneath the surface.
Use of draintile. - To secure subsurface disposal 3-inch agricultural draintile are laid with open joints, the bottom of the tile coming within 8 to 12 inches of the surface of the ground. These drains should be laid nearly level or with a very slight fall, say 2 inches in 100 feet. If too steep the lower part of the field will be flooded. The ground should be naturally or artificially so well drained that water will descend through it readily, and porous enough to admit the air. If the subsoil is not porous enough to remove all the water settling through the upper layers it should be underdrained by lines of 4-inch tile spaced from 25 to 40 feet apart. If a suitable outlet can be had these underdrains will do better work if placed 5 feet below the surface, although 4 feet will answer. The outlet should run perfectly free.
Adaptations to different soils. - The most suitable soil is a sandy loam, while clay and peat are the most unsuitable, although heavy clays can be used, where nothing else is available, by good underdraining and by filling the distributing trenches, after laying the tile, with sand, gravel, or fine cinders. The drainage will improve with time and the soil be able to purify an increased amount of sewage. The length of tile required for distributing the sewage will depend upon the porosity of the soil. For a porous soil 1 foot of tile for each gallon of sewage should dispose of the liquid. If the soil is heavier the length must be increased. For clay there should be at least 3 feet of tile per gallon.
Different methods . - There are different methods of laying out these drains, depending upon the slope of the ground. The double-chambered tank is located in the side lawn about 70 feet from the house. A 4-inch vitrified sewer-pipe line, laid with cemented joints, connects the flush tank of 300 gallons capacity with the gate valve, and two distributing lines of 3-inch draintile, each about 450 feet long, are connected to this gate valve. The character of the surface determined the direction the lines should take to give them the very slight fall required. The joints were first covered with paper to keep the dirt out of the tile until the soil became compact. The trench was partially filled with crushed stone, after the tile had been laid, to increase the porosity of the soil, and then completely filled with earth and sods replaced. At the end of each branch a little pocket of stone was placed. This system was designed to have the flush tank empty about every twenty-four hours. The distributing systems were to be used alternately, a week at a time. The gate used to change the glow from one line to the other was operated by hand, being swung from one side of the cast-iron cylinder to the other, which took about one second of time. By this means one drain is given a complete rest of a week to allow the purification of the soil.
Four and one-half cents a foot was paid for this draintile, and the price paid for the gate valve was $10, making the material for this subsurface system cost $46.50.
Another subsurface system has the settling chamber and flush tank located about 40 feet from the house. There is an advantage in placing these as close to the house as practicable. If there is any tendency for sediment to collect in the sewer, the shorter this part of the system is made the less chance there is of trouble from the stopping up of the sewer. If the system is in good working order there should be no odors. The distributing system was located on a very steep sidehill, which accounts for the method of laying the drains so as to have the branch lines of about the same length, and the average fall not much more than 2 inches in 100 feet. The 6-inch sewer pipe is laid with cemented joints, with a fall of 4 inches to the 100 feet each way from the dividing chamber. To completely empty the 6-inch sewer pipe the 3-inch drains should connect with the 6-inch pipe at the bottom.
A subsurface system adapted to lever ground has two under ground tanks are used for the sewage and a separate chamber is provided for the siphon. These tanks are placed within 15 feet of the house. As nothing is visible except the iron cover of the tanks and the system is water-tight to the place where the disposal tiles are laid, there is no sanitary reason that would require an increased distance. The tile lines are divided into three series leading from the gate, chamber, so that the ground utilized by two lines is given a complete rest while the other line is in use.
DISPOSAL BY FILTRATION
Filtration is only a more copious irrigation. The principle of purification is the same. The sewage must still be applied intermittently to allow of the renewal of the oxygen in the filter, and a preparatory treatment to remove the coarser organic matter is necessary to prevent deposits upon the surface of the filter beds. An increased quantity of sewage will be purified if the surface of the filter is raked over to the depth of an inch every week. Filters 2 and 1/2 feet deep require more attention than those of greater depth, but with proper care they serve their purpose well.
A sand filter becomes more effective the longer it is in use, if the surface is kept in good condition. For a family of five, a filter bed with a surface of from 200 to 400 square feet should give an effluent that is clear and odorless. Smaller beds can be used, but it means more care in keeping the filters clean and free from clogging, especially in winter. The filtering material should be 3 to 5 feet deep and should be well underdrained. The experiments carried on at Columbus, Ohio, indicate that the best preparatory treatment to be used with filtration methods was afforded by the septic tank, which would hold an 8-hour flow. From these experiments it would seem that the capacity of the flush tank could be reduced at least one-half if a filter bed was to be used instead of subsurface irrigation.
The sewage of a house that has a complete water carriage system is not offensive at first, because the organic matter is so small a percentage of the entire amount. If the liquid wastes can be discharged upon the surface of the ground without undue retention, this method of disposal will be without offense and entirely effective. Where plenty of land is available it is by far the cheapest and simplest method that can be used. A series of outlets should be provided to avoid saturating the ground and, as in subsurface irrigation, the application should be intermittent. This is obtained by the use of a flush tank discharging automatically by means of a siphon into a pipe leading to the disposal ground. The number of the outlets will depend upon the slope of the ground and the amount of the discharge, but it is well to have three groups of outlets to be used in succession, allowing several discharges upon one field before the gae is changed to bring another group into use. A gently sloping surface of grass land is adapted to this form of disposal without any previous preparation, except the placing of a small platform of stones or brick laid close together at each outlet to prevent the washing away of the earth and aid in spreading the flow over a greater area. The flush tank should be designed to discharge in from twelve to twenty-four hours by means of an automatic siphon.
CARE OF THE DISPOSAL PLANT
It must not be expected that once a system is installed there is nothing more to be done. Any method will require a slight amount of regular attention, but the results will amply compensate for the time and the money expended. Every part of the system, including the siphon, needs attention and occasional cleaning. Of all methods devised by the sanitary engineer for purifying sewage its application to land has secured the best results. While this method can not be used by many cities on account of the impossibility of securing a sufficient amount of suitable land, it is especially adapted to the needs of the farm.
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