WATER SUPPLY, PLUMBING, ETC., FOE COUNTRY HOMES. 35 



If the sewage is applied continuously and in such quantities that the 

 system is kept saturated, the filter or disposal area becomes water- 

 logged 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. 



DOUBLE-CHAMBER SEPTIC-TANK SYSTEMS. 



The septic tank for a small sewage-disposal system should ordi- 

 narily consist of two chambers. In this type of tank the sewage is 

 received, settled, and partially purified in one chamber and collected 

 and discharged from a second chamber. This type of tank if properly 

 designed should give satisfactory operation, since the sewage in the 

 settlmg chamber suffers little disturbance, and the discharge to the 

 final disposal system may be made intermittent by means of an auto- 

 matic siphon placed in the discharge chamber. 



Practice indicates that the settling chamber of a small septic tank 

 should have a capacity of from 5 to 15 cubic feet or from 40 to 80 

 gallons per person in the family. Some allow an average of 10 or 11 

 cubic feet per person. The best results are obtained when the 

 capacity approaches the larger limit, so that 18 to 36 hours' sewage 

 from the house may be held at one time, thus causing the sewage to 

 remain in the tank and undergo sedimentation and bacterial action 

 for this length of time. But care should be taken not to make the 

 tank so large that liquefied sewage wUl remain in it more than 36 

 hours, for in that event putrefaction is likely to set in. For this 

 reason one should make an accurate estimate of the daily sewage 

 flow, which wQl be practically equal to the daily water consumption. 

 Although a depth of 3 feet may be sufficient for some classes of sewage, 

 it is better to have the depth from 4 to 8 feet, according to the 

 number of people, in order to give the sludge a good chance to settle 

 and liquefy. The width of the chamber may ordinarily be about 

 one-third or one-half the length, although this may vary for economy 

 and convenience. The width should not be less than 3 feet, however. 



The inlet from the house should be provided with an elbow, so that 

 the discharge will be at least a foot below the contained sewage, thus 

 preventing disturbance of the surface scum. The outlet from the 

 settling chamber should be equipped in the same way. Where the 

 entrance and discharge velocities are very strong, baffle walls of 

 wood or concrete should be placed before these openings to break the 

 current. These precautions are especially beneficial in the smaller- 

 sized tanks. 



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