A Small Sewage Disposal Plant 



The Department of Agriculture tells in a bulletin how to construct a sewage 

 disposal plant for the country place. This article is an extract from that bulletin 



EXPERIENCE has shown that, in a 

 small sewage disposal system, a dark, 

 airtight tank of sufficient capacity and 

 so constructed that sewage may remain in it 

 entirely at rest for a period of from 18 to 

 24 hours, gives the best results. The solid 

 matter settles out in such a tank and, 

 according to the theory at present ac- 

 cepted, it is partially liquefied, deodor- 

 ized and destroyed by countless numbers 

 of bacteria, which thrive without air. 



In such a tank a thick scum forms on 

 the surface of the sewage, which protects 

 the bacteria from the incoming air and is 

 evidence of good bacterial action. The 

 breaking up or disturbance of this scum 

 destroys the bacterial action for the time 

 being and is likely to cause considerable 

 annoyance from bad odors. 



The septic tank effects only about 40 

 per cent purification. The liquefying 

 action in the tank, however, makes it 

 possible to subject the sewage to a final 

 treatment by filtration or distribution 



in a natural soil. This final purification 

 is effected by means of bacteria which 

 work in air. Therefore it is necessary 

 that the sewage should enter the disposal 

 system intermittently so that the sys- 

 tem may be given a chance to air out. 

 If the sewage enters continuously and 

 in such quantities that the system is 

 kept saturated, the filter or disposal area 

 becomes waterlogged and "sewage sick" 

 and ceases to be effective. It is therefore 

 necessary that the final treatment system 

 be of sufficient capacity to dispose of each 

 dose of sewage quickly. 



The septic tank for a small sewage- 

 disposal system should ordinarily consist 

 of two chambers. In this type of tank, 

 the sewage is received, settled, and par- 

 tially purified in one chamber, and col- 

 lected and discharged from a second 

 chamber. This type of tank, if properly 

 designed, should operate satisfactorily. 

 The sewage in the settling chamber suffers 

 little disturbance, and the discharge to 



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 6" THICK, ~T 



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DISCHARGE PIPE 



PUN 



ELEVATION 



Fig. 1 : The septic tank, although airtight and supposedly watertight, should be 

 located as far from the house and the well or spring, as local surroundings will permit 



461 



