The Home Medical Library Volume V Part 14

"Worcester uses chemical precipitation. In Atlanta a part of the soil is cremated, but the rest is deposited in pits 8 10 feet, and 5 feet deep. It is then thoroughly mixed with dry ashes from the crematory, and afterwards covered with either grain or gra.s.s. In Salt Lake City and in Woonsocket it is disposed of in the same way. In Indianapolis it is composted with marl and sawdust, and after some months used as a fertilizer. A portion of the sewage is cremated in Atlanta, Camden, Dayton, Evansville, Findlay, Ohio; Jacksonville, McKeesport, Pa.; Muncie, and New Brighton. In Atlanta, in 1898, there were cremated 2,362 loads of sewage. In Dayton, during 30 days, there were cremated 1,900 barrels of 300 pounds each." (_Chapin, Mun. San. in U. S._)

=The Immediate Disposal of Sewage.=--The final disposition of sewage is only one part of the problem of sewage disposal; the other part is how to remove it from the house into the street, and from the street into the places from which it is finally disposed.

The immediate disposal of sewage is accomplished by two methods--the so-called _dry_, and the _water-carriage_ methods. By the _dry method_ we mean the removal of sewage without the aid of water, simply collecting the dry and liquid portions of excreta, storing it for some time, and then removing it for final disposal. By the _water-carriage method_ is understood the system by which sewage, solid and liquid, is flushed out by means of water, through pipes or conduits called sewers, from the houses through the streets to the final destination.

=The Dry Methods.=--The dry or conservacy method of sewage disposal is a primitive method used by all ancient peoples, in China at the present time, and in all villages and spa.r.s.ely populated districts; it has for its basic principle the return to mother earth of all excreta, to be used and worked over in its natural laboratory. The excreta are simply left in the ground to undergo in the soil the various organic changes, the difference in methods being only as regards the vessels of collection and storage.

The methods are:

(1) Cesspool and privy vault.

(2) Pail system.

(3) Pneumatic system.

_The Privy Vault_ is the general mode of sewage disposal in villages, some towns, and even in some large cities, wherever sewers are not provided. In its primitive and unfortunately common form, the privy vault is nothing but a hole dug in the ground near or at some distance from the house; the hole is but a few feet deep, with a plank or rough seat over it, and an improvised shed over all. The privy is filled with the excreta; the liquids drain into the adjacent ground, which becomes saturated, and contaminates the nearest wells and water courses. The solid portion is left to acc.u.mulate until the hole is filled or the stench becomes unbearable, when the hole is either covered up and forgotten, or the excreta are removed and the hole used over again. This is the common privy as we so often find it near the cottages and mansions of our rural populace, and even in towns. A better and improved form of privy is that built in the ground, and made water-tight by being constructed of bricks set in cement, the privy being placed at a distance from the house, the shed over it ventilated, and the contents of the privy removed regularly and at stated intervals, before they become a nuisance. At its best, however, the privy vault is an abomination, as it can scarcely be so well constructed as not to contaminate the surrounding soil, or so often cleaned as to prevent decomposition and the escape of poisonous gases.

_The Pail System_ is an economic, simple, and, on the whole, very efficient method of removing fresh excreta. The excreta are pa.s.sed directly into stone or metal water- and gas-tight pails, which, after filling, are hermetically covered and removed to the places for final disposal. This system is in use in Rochedale, Manchester, Glasgow, and other places in England.

The pails may also be filled with dried earth, ashes, etc., which are mixed with the excreta and convert it into a substance fit for fertilization.

_The Pneumatic System_ is a rather complicated mechanical method invented by Captain Lieurneur, and is used extensively in some places.

In this system the excreta are pa.s.sed to certain pipes and receptacles, and from there aspirated by means of air exhausts.

=The Water-carriage System.=--We now come to the modern mode of using water to carry and flush all sewage material. This method is being adopted throughout the civilized world. For it is claimed a reduction of the mortality rate issues wherever it is introduced. The water-carriage system presupposes the construction and existence of pipes from the house to and through the street to the place of final disposition. The pipes running from the house to the streets are called house sewers; and when in the streets, are called street sewers.

=The Separate and Combined Systems.=--Whenever the water-carriage system is used, it is either intended to carry only sewage proper, viz., solid and liquid excreta flushed by water, or fain water and other waste water from the household in addition. The water-carriage system is accordingly divided into two systems: _the combined_, by which all sewage and all waste and rain water are carried through the sewers, and the _separate_ system, in which two groups of pipes are used--the sewers proper to carry sewage only, and the other pipes to dispose of rain water and other uncontaminated waste water. Each system has its advocates, its advantages and disadvantages. The advantages claimed for the separate system are as follows:

(1) Sewers may be of small diameter, not more than six inches.

(2) Constant, efficient flow and flushing of sewage.

(3) The sewage gained is richer in fertilizing matter.

(4) The sewers never overflow, as is frequently the case in the combined system.

(5) The sewers being small, no decomposition takes place therein.

(6) Sewers of small diameter need no special means of ventilation, or main traps on house drains, and can be ventilated through the house pipes.

On the other hand, the disadvantages of the separate system are:

(1) The need of two systems of sewers, for sewage and for rain water, and the expense attached thereto.

(2) The sewers used for sewage proper require some system for periodically flushing them, which, in the combined system, is done by the occasional rains.

(3) Small sewers cannot be as well cleaned or gotten at as larger ones.

The separate system has been used in Memphis and in Keene, N. H., for a number of years with complete satisfaction. Most cities, however, use the combined system.

CHAPTER V

=Sewers=

=Definitions.=--A sewer is a conduit or pipe intended for the pa.s.sage of sewage, waste, and rain water.

A _House Sewer_ is the branch sewer extending from a point two feet outside of the outer wall of the building to its connection with the street sewer, etc.

=Materials.=--The materials from which sewers are manufactured is earthenware "vitrified pipes."

Iron is used only for pipes of small diameter; and as most of the sewers are of greater diameter than six inches, they are made of other material than iron.

Cement and brick sewers are frequently used, and, when properly constructed, are efficient, although the inner surface of such pipes is rough, which causes adherence of sewage matter.

The most common material of which sewers are manufactured is earthenware, "vitrified pipes."

"Vitrified pipes are manufactured from some kind of clay, and are salt-glazed inside. Good vitrified pipe must be circular and true in section, of a uniform thickness, perfectly straight, and free from cracks or other defects; they must be hard, tough, not porous, and have a highly smooth surface. The thicknesses of vitrified pipes are as follows:

4 inches diameter 1/2 inch thick 6 " " 1/16 " "

8 " " 3/4 " "

12 " " 1 " "

The pipes are made in two- and three-foot lengths, with spigot, and socket ends." (Gerhardt.)

Sewer pipes are laid in trenches at least three feet deep, to insure against the action of frosts.

=Construction.=--The level of the trenches in which sewers are laid should be accurate, and a hard bed must be secured, or prepared, for the pipes to lie on. If the ground is sandy and soft, a solid bed of concrete should be laid, and the places where the joints are should be hollowed out, and the latter embedded in cement.

=Joints.=--The joints of the various lengths must be gas-tight, and are made as follows: into the hub (the enlargement on one end of the pipe) the spigot end of the next length is inserted, and in the s.p.a.ce left between the two a small piece, or gasket, of oak.u.m is rammed in; the remaining s.p.a.ce is filled in with a mixture of the best Portland cement and clean, sharp sand. The office of the oak.u.m is to prevent the cement from getting on the inside of the pipe. The joint is then wiped around with additional cement.

=Fall.=--In order that there should be a steady and certain flow of the contents of the sewer, the size and fall of the latter must be suitable; that is, the pipes must be laid with a steady, gradual inclination or fall toward the exit. This fall must be even, without sudden changes, and not too great or too small.

[Ill.u.s.tration: FIG. 15.

A BRICK SEWER.]

The following has been determined to be about the right fall for the sizes stated:

4-inch pipe 1 foot in 40 feet 6 " " 1 " " 60 "

9 " " 1 " " 90 "

12 " " 1 " " 120 "

=Flow.=--The velocity of the flow in sewers depends on the volume of their contents, the size of the pipes, and the fall. The velocity should not be less than 120 feet in a minute, or the sewer will not be self-cleansing.

=Size.=--In order for the sewer to be self-cleansing, its size must be proportional to the work to be accomplished, so that it may be fully and thoroughly flushed and not permit stagnation and consequent decomposition of its contents. If the sewer be too small, it will not be adequate for its purpose, and will overflow, back up, etc.; if too large, the velocity of the flow will be too low, and stagnation will result. In the separate system, where there is a separate provision for rain water, the size of the sewer ought not to exceed six inches in diameter. In the combined system, however, when arrangements must be made for the disposal of large volumes of storm water, the size of the sewer must be larger, thus making it less self-cleansing.