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Encyclopedia Britannica - Main :: SCY-SHA |
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SEWERAGE , a general term for the process of systematically collecting and removing the fouled water- supply of a community. The matter to be dealt with may conveniently be classified as made up of three parts: (I) excreta, consisting of urine and faeces; (2) slop-water, or the discharge from sinks, basins, baths; &c., and the waste water of industrial processes; (3) surface; water due to rainfall. Before the use of underground conduits became general, the second and third constituents were commonly allowed to sink into the neighbouring ground, or to find their way by surface channels to a watercourse or to the sea. The first constituent was conserved in middens or pits, either together with the dust, ashes, kitchen waste and solid waste generally or separately, and was carried away from time to time to be applied as manure to the land. In more modern times the pits in which excrement was collected took the form of covered tanks called cesspools, and with this modification the primitive system of conservancy, with occasional removal by carts, is still to be found in many towns. Even where the plan of removing excrement by sewers has been adopted, the kitchen waste, ashes and solid refuse is still treated by collecting it in pails or bins, whose contents are removed by carts either daily or at longer intervals, the refuse frequently being burned in destructors (q.v.). It therefore forms no part of the nearly liquid sewage which the other constituents unite to form.The first constituent is from an agricultural point of view the most valuable, and from a hygienic point of view the most dangerous, element of sewage. Even healthy excreta decompose, if kept for a short time after they are produced, and give rise to noxious gases; but a more serious danger proceeds from the fact that in certain cases of sickness these products are charged with specific germs of disease. Speedy removal or destruction. of excremental sewage is therefore imperative. It may be re-moved in an unmixed state, either in pails or tanks or-(with the aid of pneumatic pressure) by pipes; or it may be defaecated by mixture with dry earth or ashes; or, finally, it may be conveyed away in sewers by gravitation, after the addition of a relatively large volume of water. This last mode of disposal is termed the water-carriage system of sewerage. It is the plan now usually adopted in towns which have a sufficient water supply , and it is probably the mode which best meets the needs, of any large community. The sewers which carry the diluted excreta serve also to take slop-water, and may or may not be used to remove the surface water due to rainfall. The water-carriage system has the disadvantage that much of the agricultural value of sewage is lost by its dilution, while the volume of foul matter to be disposed of is greatly increased.I. COLLECTION OF SEWAGE. HOUSe
those parts of the domestic system of drainage which extend from the soil-pipes and waste-pipes to the sewer, are generally made of glazed stoneware pipes having a diameter of 4 in., 6 in., or sometimes 9 or 12 in., according to the estimated amount ofwaste to be removed. In ordinary domestic dwellingsthere is rarely any occasion to use pipes of a greater diameter than 6 in., andthis only for the main drain, the branches and single lines of piping being 4 in. in dia- meter
make the pipes and other fittings, such as channels and bends, as small in diameter as possible, having due regard to efficient capacity. Such a drain is more cleanly than one too large for its purpose, in that it is more thoroughly flushed when in use, the sewage running at a much faster speed through a full pipe than through one only partially full. For this reason a pipe having too great a capacity for the b(tuman j work it has to do is liable to become corroded by sedi- ment deposited from slowly moving waste. The pipes are made in 2 ft. lengths and are formed with a socket at one end into which the straight end of This is wedged in position with a little gasket and the remaining space then carefully filled with neat Portland
bitumen
bitumen
ordinary Portland
shows the method of connect- car n /`l/`"/'sr/~ bii'turr 2t1 ing a lead pipe into the socket rarauuuaariuraaia/a. %uiouriaiaraiit of a stoneware one, a brass sleeve piece or ferrule being slon~raKG used to give the necessary stiffness to the end of the lead pipe. This arrangement is 11u1111(11 II1111I i %:,~/ frequently used, for example, at the base of a soil-pipe at its junction with the drain. In lead pipe has a brass socket 9 t fPNVUt2 11111111 attached to it to take the plain end of a stoneware pipe. This form of connexion is used between a water-closet and a lead trap. The joint shown in figs. 5 and 6 is similarly made when an iron pipe is substituted for a stoneware one, but instead of the Portland cement filling, molten lead is used and carefully caulked to form a water-tight joint. In the water-carriage system of drainage each house
sinks, lavatory basins, and rain-water and other gulleys within and about the house. The many branches are II II, gathered into one or more manholes, and connexion is finally made by means of a single pipe with the common public sewer. Gas from the sewer is prevented from entering the house drains by a disconnecting trap fixed in the manhole nearest the entrance to the sewer. The fundamental maxims of house sanitation are first, that there shall be complete disconnexion between the pipes within and without the house, and second, that the drainage shall be so constructed as to allow for the free admission of air in order to secure the thorough ventilation of all parts of the system lead HIJIIItt II 111111111 1ad' I 1 J 1(11111 fitted with open channels instead of closed pipes. This allows of easy inspection and testing, and provides means of access for the drain-rods in cases of blockage. Some-times it is desired, for reasons of economy
change of direction in the drain. A branch pipe which may have a specially shaped junction for cleaning the pipes in both directions is taken up with a slope to the ground or floor level and there finished with an air-tight cover which may be removed to allow the introduction of drain-rods should the pipes become blocked. Junctions of one pipe with another should be madeobliquely in the direction 'cement of the floor. Stoneware pipes should be laid upon a bed of concrete not less than 6 in. thick and benched up at the sides with concrete to prevent pipes pass under a building they should be entirely surrounded by a concrete casing at least 6 in. in thickness. No drain should lie under a building if it is possible to avoid it, for injury is very liable to occur through some slight settlement of the building, and in a position such that the smells escaping from the damaged pipe would rise up through the floor into the building this would be an especially serious matter. The expense and annoyance of having the ground opened up for the repair of defects in the pipes beneath is another strong argument against drains being placed under a house. Where this is really necessary, however, pipes of cast-iron are recommended instead of the ordinary stoneware pipes, as being stronger; being made in lengths of 6 and 9 ft., they have a great advantage over the 2 ft. long stoneware tubes, for the joints of the latter are frequently a source of weakness. The joints, fewer in number, are made with molten lead (fig. 7), or flanged pipes are used and the joints packed with rubber and bolted (fig. 8). The principle of disconnexion adopted between the indoor and outdoor pipes should be retained between the latter and the sewer, and the domestic system should be cut off from the public drain by means of a disconnecting trap. This appliance is usually placed in a small chamber or manhole, easy of access for inspection, built close to the boundary of the premises, and as near as possible to the sewer into which the house drain discharges. Fig. 9 shows a section and plan of such a manhole built in accordance with the London drainage by-laws. There are five inlets from branch drains discharging by specially-shaped glazed channels into the main channel in the centre. It will be seen that in case of blockage it would be a simple matter to clear any of the pipes with n/1111/iaiirr,rr :n/,, ' 9lan?xvate, 5tonamatt, ~ttlltt(IIIIUI `1111111111 (I1111(Ill( atone.rrates elonc.nrot 'lllllll111(1111 IIII(I1i I++11111111 geo lsin iron iron W (II1((ll(III Illllt} 1((11101(1( FIG. 7.Iron Spigot and Socket Joint. ~tlttttl(Uglllll ~I II iron 0. ivron -n111111ttI(~ Bolted the drain=rods. The cap to the cleanng arm has a chain attached by which it can be removed in case of flooding. The channels are benched up at the sides with cement, and the manhole is rendered on the inside with a cement lining. A fresh air inlet is taken out near the top of the chamber and is fitted with a mica flap inlet valve. The cover is of cast-iron in a cast-iron frame
The water-carriage system of drainage is undoubtedly the most nearly perfect yet devised. At the same time it is a very costly system to install with its network of sewers, pumping stations, and arrangements for depositing the sewage either in the sea or river, or upon the land or " sewage farm." In country districts and small towns and villages, however, excreta are often collected in small vessels End of Article: SEWERAGE If you wish, you can link directly to this article.
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