SEWAGE AND SEWERAGE 



5322 



SEWAGE DISPOSAL ON FARMS 



a second. Where the ground is quite level, it 

 is sometimes necessary to facilitate the flow by 

 means of pumps. The decomposition of sewage 

 gives rise to poisonous gases, and in the interest 

 of health sewers are ventilated; that is. shafts 

 with iron gratings are placed at frequent inter- 

 vals so that air may reach the conduits. When 

 these are large enough to permit a man to 

 descend to clean or inspect the sewer, they are 

 called manholes. Such manholes are placed at 

 each change of direction of the conduits and 

 at junctions with the branches. Not all the 

 gas, of course, escapes through the shafts; it is 

 customary, therefore, to protect sinks and wash- 

 bowls from an influx of gas by fitting an elbow 

 in the pipe, which holds enough water to ex- 

 clude noxious fumes. 



When cities are situated on the seaboard or 

 the shores of large lakes, the sewerage system 

 usually empties into deep water. Rivers are 

 also used for this purpose, for it has been 

 proved that after a flow of five miles through 

 running water thorough purification has resulted. 

 With the enormous growth of American and 

 Canadian cities, however, this generally prevail- 

 ing practice has sometimes resulted in a cer- 

 tain amount of water pollution, due to vast 

 quantities of sewage and lack of sufficient water 

 to purify it. Of recent years increased atten- 

 tion has been given to scientific methods of 

 sewage disposal practiced in England and on 

 the continent of Europe. There the sewage is 

 often treated with chemicals in huge tanks, 

 lime alone or lime in conjunction with alumi- 

 num or ferrous sulphate being used as a puri- 

 fier. Septic tanks and contact beds or sand and 

 percolating filters are becoming increasingly 

 common. In the tanks, bacteria convert harm- 

 ful organic matter into harmless minerals. 

 Contact beds are water-tight compartments, 

 filled with broken stone or clinkers, in which the 

 sewage is acted upon by bacteria and purified. 

 Such methods of clarifying sewage are expensive 

 and have not yet been widely adopted in the 

 United States or Canada. 



Besides the sewage, there is a considerable 

 amount of waste matter, such as ashes and gar- 

 bage, which cannot be disposed of by the sewer- 

 age system. This is collected in carts and 

 burned at incinerating plants or deposited 

 where it cannot do harm. In the more scientific 

 method of disposal, reduction plants convert 

 much of this waste into grease ard other salable 

 commodities. G.B.D. 



Consult Kershaw's Modern Methods of Sewage 

 Purification; Easdale's Sewage Disposal Works. 



Related Subjects. The reader is referred to 

 the following articles in these volumes: 

 Garbage Sewage Disposal on 



Sanitary Science Farms 



Well Boring: 



SEWAGE DISPOSAL ON FARMS. Owing 

 to engineering progress, people now dwelling in 

 the rural districts may without undue expense 

 enjoy the convenience of running water in the 

 home. Many farmers and suburban dwellers, 



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A SEPTIC TANK 



Sewage enters at one side and is prevented by 

 the baffle boards from causing a direct flow 

 across the tank. When the settling tank is full 

 any excess trickles into the discharge tank. As 

 this gradually fills, the air in the cap of the 

 siphon is compressed until it suddenly forces out 

 the contents of the siphon, drawing after it the 

 water in the discharge tank. The pressure of 

 the air in the air pipe prevents the absolute ex- 

 haustion of water from the siphon, which would 

 cause a gradual instead of a sudden discharge. 



however, though aware of their ability to in- 

 stall pumping machinery, refrain from doing so 

 because they do not know what to do with 

 their sewage. But here, too, science has come 

 to their aid, by devising schemes for employing 

 the purifying forces of nature. 



The chief danger from unscientific handling 

 of drainage, as in carelessly built, old-fashioned 

 cesspools, is, of course, contamination of wells. 

 But under the system here described, and un- 

 der many others which have been designed by 

 scientific men for special conditions, sewage 

 may be handled with even better results than 

 are obtained in cities. 



This system combines what is known as a 

 septic tank and subsurface irrigation. Its ef- 

 fectiveness arises from the fact that in all sur- 

 face soil there are certain bacteria which are 

 able to render waste matter harmless if it is 

 liquefied and well distributed. 



The sewage first enters the septic tank, which 

 is closed both to air and to light, and here in 

 a period of twelve hours or more its own bac- 

 teria break up most of the solid matter. The 

 tank is usually of brick, concrete or steel, and 

 ought to be far enough in the ground so that 



