EXCRETA DISPOSAL The term excreta is a collective one, applied to both human feces and urine. These discharges have a direct relationship to health for the following reasons: (a) Several different species of infective agents leave the body by this means, from which they may be transmitted to other persons by the agencies of contact, contamination of water supplies with excreta, and by the contamination of house flies with excreta.
(b) In addition, lack of care in the collection and removal of these discharges will give rise to collections of decomposing organic matter about habitations, which are exceedingly offen sive to the senses. In other words, it then constitutes a nuisance.
1. Modern Urban Methods of Excreta neces sity for these methods has arisen from the extreme congestion of urban population which characterizes the present era. Ur ban sewer systems were originally devised for the removal of storm and ground water, not for the removal of excreta. Thus not until 1815 was fecal matter permitted in the London sewers, in 1833 in Boston and in 188o in Paris. Water closets as we know them, date from the report of the English Health of Town's Commission in 1844 and were not connected with sewers until 1847. The successful employment of water closets requires that an abundant supply of water under pressure be available, inasmuch as the solid fecal debris is transported in the sewers, particularly the house drains and lateral sewers, by the velocity of the water current. Hence the present system of excreta removal widely employed in our cities and towns is known as the water carriage system.
2. is the term applied to the under ground system of drains by which excreta is removed inoffen sively. While the development of such systems has relieved a certain set of sanitary problems by removing these offensive accumulations from around urban dwellings, yet the transporta tion of the excrement of an entire city without its bounds, and its concentration at one or a few points has given rise to an entirely new set of problems, which we shall consider later.
In a consideration of a sewerage system certain terms are used, which we will define here: (a) A combined sewerage system is one that receives both domestic sewage as well as the surface wash of the streets, known as storm water.
(b) Sanitary sewers are those that receive domestic sewage alone.
(c) Storm sewers are those that receive storm water or street washings alone.
The last two systems are the best where methods of sewage treatment are employed, inasmuch as the large volumes of storm water interfere seriously with the operation of the sewage disposal plants.
A sewerage system consists of the following components, the names of which are self explanatory. Starting at the dwell ings we have the house drains, which discharge into the lateral sewers, which in turn discharge into the trunk sewers, which carry the excreta to the point of disposal. Trunk sewers may be connected to intersecting sewers which carry the excreta still further away.
3. Sewage.—Sewage is the material which flows through the sewers. It consists of the waste water supply, plus ground water leakage into the sewers plus domestic water wastes, plus excreta, plus industrial wastes and perhaps storm water in addition. In dry weather its volume approximates the daily water consumption of the community. Per capita its daily volume in small towns will be from 4o to so gallons, in large cities from roc to 200 gallons. Per capita its average composi tion will be about the following: Average daily water consumption 285,000 gms.
Fecal solids ioo gms.
Urinary solids so gms.
Miscellaneous solids Soo gms.
From the standpoint of its composition we may consider sewage to be a more or less homogenous suspension of fine particles with organic and mineral matter in solution. The organic matter present is very unstable so that its chemical composition is variable, depending on the age of the material. Important organic constituents are urea, albumen, fibrin, casein, starch, sugar, fats, and soaps. Of the elemental substances present nitrogen and sulphur are of the greatest importance.